EnVision is ESA’s next mission to Venus in partnership with NASA, where NASA provides the Synthetic Aperture Radar payload and mission support for critical phases [1]. The mission was adopted in January 2024, and ESA awarded Thales Alenia Space (TAS) the contract to build the Envision spacecraft on 28 January 2025. The launch is scheduled for 2031, and the science operations at Venus would start in summer 2034, after the mission cruise and aerobraking phase around Venus to achieve a low Venus polar orbit. EnVision will provide a holistic view of the planet from its inner core to its upper atmosphere, studying the planets history, geological activity and climate. It aims to establish the nature and current state of Venus’ geological evolution and its connection with the atmosphere. The overall science objectives are to: (i) characterize the sequence of events that formed the regional and global surface features of Venus, as well as the geodynamic framework that has controlled the release of internal heat over Venus history; (ii) determine how geologically active the planet is today; (iii) establish the interactions between the planet and its atmosphere at present and through time. Furthermore, EnVision will look for evidence of past liquid water on the planet surface.

The nominal science phase of the mission will last six Venus cycles (~four Earth years), and ~210 Tbits of science data will be downlinked using a Ka-/X-band communication system. The science objectives will be addressed by five instruments and one experiment, provided by ESA member states and NASA. The NASA provided VenSAR S-band radar will perform targeted surface imaging as well as polarimetric and stereo imaging, radiometry, and altimetry. The high-frequency Subsurface Radar Sounder (SRS) will sound the upper crust in search of material boundaries for the first time. Three spectrometers, VenSpec-U, VenSpec-H and VenSpec-M, operating in the UV and Near- and Short Wave-IR, respectively, will map trace gases, search for volcanic gas plumes above and below the clouds, and map surface emissivity and composition. A Radio Science Experiment (RSE) investigation will exploit the spacecraft Telemetry Tracking and Command (TT&C in Ka-/X bands) system to determine the planet’s gravity field and to sound the structure and composition of the middle atmosphere and cloud layer in radio occultation. ASI, DLR, BelSPO, and CNES lead the procurements of the SRS, VenSpec-M, VenSpec-H and VenSpec-U instruments and the Radio Science Experiment (RSE), respectively. All instruments have heritage and robust margins relative to the requirements, with designs suitable for operation in the Venus environment, and were chosen to meet the broad range of measurement requirements needed to support the EnVision scientific objectives. The EnVision science teams will adopt an open data policy, with public release of the scientific data after validation and verification. Public calibrated data availability are provided <6 months after data downlink.

In 2024, the Envision Science Working Team and its appointed Regions of Interest (ROI) Working Group started to work on a refined version of the Venus ROIs to be observed by the instruments and experiment. In particular, the planning of the VenSAR SAR imaging observations requires careful preparation and optimization, due to the high data rates and inter-planetary downlink limitations, balancing the observation needs between the mission instruments and experiment. Further activities include the maturation of the instrument and mission design, science performance simulations and confirmation, definition and preparations of the characterization, calibration, operations and data processing. Finally, the Envision science community is steadily growing with several scientific activities on-going to prepare for mission data exploitation.

The scientific objectives, instrumentation, and status of the EnVision mission will be presented, including an overview of on-going scientific and technical activities and the next steps in the mission preparation.

Acknowledgements: The Envision instrument (science) teams, further project team members, and industry partners.

References:

[1] ESA (2023): EnVision, Understanding why Earth’s closest neighbour is so different, ESA Definition Study Report, https://www.cosmos.esa.int/web/envision/links.

How to cite: Straume-Lindner, A. G., Schulte, M. D., and Pacros, A. and the Envision Science Working Team (SWT) and Project Teams: The EnVision Mission to Venus – mission overview and science preparations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-850, https://doi.org/10.5194/epsc-dps2025-850, 2025.

Why did Venus, once likely similar to Earth, evolve into a scorching world with a dense, toxic atmosphere? In the coming decade, Venus will be in the spotlight, with a new generation of missions descending through its clouds or probing its surface to explore its geologic past in search of answers. However, one critical part of the puzzle remains: How has the long-term influence of the space environment affected the evolution of Venus’ atmosphere?

Inanna, a new mission proposed to the European Space Agency’s M8 call, is designed to address this missing piece of the puzzle. It is the first mission fully dedicated to comprehensively investigate how the interplay between the solar wind and the Venusian ionosphere, the ionised uppermost part of the atmosphere, has driven atmospheric escape over time. Inanna is a two-spacecraft mission: the main Venus Orbiter, carrying instruments for in situ measurements of ions, neutrals, and electromagnetic fields, and the Solar Wind Monitor, which will spend most of its time in the solar wind to continuously characterize the solar wind and interplanetary magnetic field. This unique configuration will finally provide us with the means to disentangle the temporal variations in solar forcing from spatial structures in Venus’ induced magnetosphere, and give us solid evidence for how the Venusian atmosphere has evolved via interactions with outside forces through time.

By capturing both the drivers and the planetary response, Inanna will characterize the dynamic processes that accelerate and remove particles from Venus’ upper atmosphere. Deep dip campaigns of the Venus Orbiter, reaching down to or below the ionospheric peak at ~150 km, will show how energy and momentum from the solar wind couple into the atmosphere, and how atmospheric escape varies with region, composition and solar conditions. In addition, instruments to measure winds, temperature, and composition in the upper mesosphere, thermosphere, and ionosphere will help assess how energy and momentum may propagate upward from lower atmospheric layers.

While other upcoming missions focus on the history of Venus’ interior and lower atmosphere, Inanna complements and extends them by offering crucial insight into what has been lost to space and how that loss has occurred. Understanding this is essential to piecing together the full story of Venus’ transformation through time. In this presentation we will highlight the Inanna mission concept, its scientific goals, and how we plan to achieve them.

How to cite: Persson, M. and the Inanna mission core team: Inanna: Decoding the Role of Space in Venus’ Atmospheric Evolution Through Time, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-649, https://doi.org/10.5194/epsc-dps2025-649, 2025.

Measuring the abundances of noble gases and their isotope ratios in Venus atmosphere is an essential investigation to understand Venus global evolution [1]. We propose a small satellite concept (ESA F-type mission) that would skim through Venus atmosphere below the homopause to collect samples that will be brought back to Earth and analyzed by the most sophisticated instruments in international laboratories. The science objectives are to determine the origin and geological evolution of Venus and to assess its potential habitability in the past. They are critical in the context of exoplanets detection to assess whether a terrestrial exoplanet is more likely to be Earth-like or Venus-like, which has profound astrobiological implications.

This mission concept has been proposed in response to the ESA call for F3 mission. It has matured from previous mission concepts [2]. It has also beneficiated from targeted work on the fractionation of noble gases during high velocity sampling [3]. Finally, a recent study by a CNES team showed that such a mission is feasible within the constraints (launch vehicle, mass, cost, …) of the ESA F3 call.

We show that measurements of key elemental ratios of noble gases and of Kr and Xe isotopes at high precision in ground-based laboratories would allow determining the origin of Venus’ atmosphere but will also put constraints on how much xenon has been escaping during hydrogen escape episodes. Measurements will also be able to put constraints on the time of outgassing of Venus’ interior into the atmosphere via measurements of radiogenic excesses of noble gas isotopes produced by extinct (¹²⁹I) and extant (²³⁸U) radionuclides.

The two main consequences of hyper-velocity sampling are: i) molecules are likely to be dissociated due to the high-enthalpy flight regime; ii) the atmospheric samples will be fractionated due to differential diffusion in the flow path. Numerical simulations [3] show that elemental and isotopic fractionations are mass-dependent and can be accounted for. Importantly, simulation results show that the isotopic ratios of xenon, due to its high mass, are little affected by fractionation. It highlights the complementarity between VATMOS-SR and the NASA DAVINCI mission with the later providing the in-situ density and the former the exquisite resolution on the isotopic ratios that is required to answer the science questions.

The VATMOS-SR mission would launch in July 2034 and would bring back the samples one year later. Samples will be distributed to European and other international partners for measurements to be performed within a couple of years after landing. This sample return mission may be the first return of a planetary sample.

[1] Avice et al. (2022) Space Science Reviews 218, 60. doi:10.1007/s11214-022-00929-9 [2] Sotin, et al. (2019) EPSC-DPS Joint Meeting 2019, EPSC–DPS2019–989. [3] Borner et al. (2025) submitted.

How to cite: Sotin, C., Avice, G., Parai, R., Borner, A., Francastel, A., Lebonnois, S., Rabinovitch, J., and Rocard, F.: VATMOS-SR: A Fast Mission to Return Samples from Venus Atmosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1588, https://doi.org/10.5194/epsc-dps2025-1588, 2025.

The ESA EnVision mission aims to provide a comprehensive understanding of Venus by investigating its geology and atmosphere, seeking to uncover why Venus and Earth, despite their similarities, have experienced such different evolutionary paths. 
A key payload on EnVision is the VenSpec Suite, designed to deliver unprecedented insights into Venus’ geological activity, atmospheric composition, and surface evolution. By targeting signatures of volcanic activity and mapping both surface and atmospheric features, VenSpec will seek to understand the processes shaping Venus today and in the past, and to provide insights into the evolution and habitability of terrestrial planets

The VenSpec Suite Instruments: The VenSpec Suite is following the holistic approach of the EnVision mission by studying the coupled system of surface and atmosphere on Venus with three complementary instruments, VenSpec-M, VenSpec-H, VenSpec-U and a Central Control Unit (CCU):

• VenSpec-U is an ultraviolet spectral imager (at low and high spectral resolution between 190 and 380 nm) [1]. By probing how volcanic outgassing and atmospheric dynamics interact through the upper cloud level, VenSpec-U complement and enhance the VenSpec-H and VenSpec-M observations.
• VenSpec-H is an infrared spectrometer, with four spectral bands in the near IR between 1.16 and 2.48 μm, that will provide measurements of atmospheric gases in the troposphere and mesosphere of Venus at high spectral resolution [2]. These observations will help identify volcanic plumes and gas exchanges with the surface, in coordination with VenSpec-M and VenSpec-U. Polarization filters are also included in the design to characterize the hazes in the mesosphere.
• VenSpec-M is a multispectral imaging spectrometer in 14 near-IR transparency windows (0.79–1.51 μm). It will observe the Venus surface across five atmospheric windows around 1 μm and monitor the planet for volcanic activity using clouds and water vapor bands [3]. To retrieve calibrated emissivity data from the Venus surface, VenSpec-M will utilize improved topography from NASA VERITAS’s VISAR and EnVision’s VenSAR-derived Digital Elevation Models (DEMs).
• The CCU is a simple and robust interface to the spacecraft, providing an abstraction layer between the channels and the spacecraft. The CCU offers a harmonized power and data interface to the spacecraft and allows the channels to design a simple, tailored internal interface to the CCU [4].

VenSpec Scientific Objectives: VenSpec will deliver crucial data for understanding Venus’ present state and evolutionary history, with the following primary objectives:

• Comprehensive Volcanic Activity Search - VenSpec will perform a thorough search for volcanic activity by detecting atmospheric, thermal, and compositional signatures, as well as by mapping surface composition globally;
• Atmosphere-Surface Coupling – The VenSpec suite is designed to follow volcanic plumes from their source near the surface (VenSpec-M, VenSpec-H) through the middle atmosphere (VenSpec-H) and up to the cloud tops (VenSpec-U), offering a holistic view of gas exchanges and atmospheric processes;
• Tropospheric trace gases - VenSpec-H will detect and quantify key volcanic and cloud-forming gases (SO₂, H₂O, HDO, OCS, CO, HCl) in the atmosphere, lower and upper;
• Surface Composition - VenSpec-M will provide near-global data on rock types and surface weathering, helping to understand crustal evolution and the history of volcanic resurfacing;
• Upper Atmosphere Studies - VenSpec-U and -H will monitor trace gases (CO, H₂O, OCS, SO, SO₂), cloud top altitude and the mysterious UV absorber in the upper clouds, shedding light on atmospheric chemistry and its links to volcanism

The VenSpec Joint Science Team: The VenSpec Suite is coordinated by a joint science team that ensures seamless integration and cooperation among the instruments. Rather than by channel, the science team is organized into interdisciplinary working groups that leverage synergies across all channels and foster collaboration among researchers and institutions. This structure enables more holistic investigations and promotes the sharing of data, models, and expertise.

Six cross-instrument Working Groups (WG) are currently actively engaged in preparatory science activities:

• Solar-Related Studies WG – focuses on a coordinated work to obtain good solar calibration and absolute measurements especially for VenSpec-U and VenSpec-H;
• Regions Of Interest WG – joints effort to produce a VenSpec targets list as input for the EnVision Regions Of Interest list based on scientific rationales and EnVision science requirements [5];
• Laboratory Investigations WG - supports the suite through laboratory experiments that simulate Venus’ surface and atmospheric conditions. The group fosters synergies between different laboratories and experimental approaches, providing essential reference data for instrument calibration and interpretation [6].
• Atmospheric Modelling WG – investigates models of Venus’ atmosphere, including cloud chemistry, sulfur processes (e.g., in-droplet S chemistry), and tropospheric and mesospheric SO₂ dynamics. Provide key chemical species vertical profiles to the Radiative Transfer WG.
• Radiative Transfer WG – focuses on radiative transfer codes intercomparison, i.e. methods, approximations and applications will be discussed.
• Ground-Based Observations WG - acts as a bridge between the Venus observation community and the radiative transfer modeling team. This group coordinates ground-based monitoring of atmospheric variability and dynamics, and advocates for Venus observations that complement space-based measurements [7].

These groups aim to address the most pressing questions about Venus’ surface and atmosphere through coordinated scientific strategies.

References: [1] Marcq et al. (2025, this meeting); [2] Robert et al. (2025, this meeting?); [3] Alemanno et al. (2025, this meeting); [4] Fitzner et al. (2024), SPIE Proc. 131440D. [5] Barraud et al. (2025a, this meeting); [6] Barraud et al. (2025b, this meeting); [7] Hueso et al. (2025, this meeting)

How to cite: Alemanno, G., Robert, S., and Marcq, E. and the VenSpec Team: Synergistic Observations of Venus’ Surface and Atmosphere: The Role of VenSpec on the ESA EnVision Mission, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1409, https://doi.org/10.5194/epsc-dps2025-1409, 2025.

Airglow emissions in the upper atmosphere of Venus offer valuable tracers for probing atmospheric dynamics between 90 and 120 km. The 1.27 μm O₂ airglow, which contribution function is near 95 km altitude, is particularly useful as it lies in the transition region at the interface of two distinct circulation regimes: the retrograde super-rotating zonal flow (RSZ) below ~100 km and the sub-solar to anti-solar (SSAS) circulation above. Convergence of the SSAS near the anti-solar point results in O₂ airglow from the downwelling excited O₂. Although often concentrated at equatorial midnight, peak fluxes are often observed morning-ward of midnight, and exhibit excursions to high latitudes. Observations from ESA's Venus Express (2006–2014), particularly from the VIRTIS instrument, highlighted this complexity and revealed a secondary brightness maximum at ~30°N and ~50°N—features not captured by current global circulation models. Recent modeling efforts, however, suggest that periodic atmospheric waves, such as a ~5-day Kelvin wave, may modulate the O₂ nightglow’s intensity and latitudinal structure.

We present a novel approach using ground-based infrared spectroscopy with the NASA IRTF SpeX instrument to detect and analyze Venus’ O₂ nightglow at 1.27 μm. While the SpeX dataset (2001–present) was originally aimed at cloud studies, it includes regular detections of the O₂ airglow, typically two images per night during Venus observations. By scanning the slit across the planet's disk, we retrieve spatially resolved airglow signals on both the disk and limb, as shown in Figure 1.

Figure1. IRTF SpeX reconstructed images of the O₂ (a¹Δ_g) 1.27 mm airglow showing a hint of a 5-day pattern over a series of images taken between 09-06-2023 and 09-11-2023. On all images, the North is located to the left of the image, the South is to the right. The saturated crescent area represents the dayside of Venus, while the airglow is visible as white patches along the limb and on the disk on the nightside.

Our analysis focuses on extracting temporal and spatial variations in the O₂ emission across a range of observation periods—before, during, and after the Venus Express mission—offering new constraints on atmospheric variability. The data allow for short-term morphology analysis on nights with multiple images and support long-term trend studies over a 23-year period. These ground-based results complement spacecraft datasets and enable us to evaluate model predictions, including those involving Kelvin wave-driven modulation of the nightglow.

This work demonstrates the value of archived ground-based observations for planetary atmosphere studies and provides an important, underutilized dataset for understanding the structure and variability of Venus' upper atmosphere.

References

Gérard, J.-C., Soret, L., Saglam, A., Piccioni, G., Drossart, P. (2010), The distributions of the OH Meinel and O₂ (a¹ – X³Σ) nightglow emissions in the Venus mesosphere based on VIRTIS observations. Adv. Space Res. 45, 1268–1275, doi:10.1016/j.asr.2010.01.022

Gérard, J.-C., Soret, L., Piccioni, G., Drossart, P. (2014), Latitudinal structure of the Venus O₂ infrared airglow: a signature of small-scale dynamical processes in the upper atmosphere. Icarus 236, 93–103, doi:10.1016/j.icarus.2014.03.028

Navarro, T., Gilli, G., Schubert, G., Lebonnois, S., Lefèvre, F., & Quirino, D. (2021). Venus’ upper atmosphere revealed by a GCM: I. Structure and variability of the circulation. Icarus, 366, 114400.

Evodkimova, D., Fedorova, A., Zharikova, M., Montmessin, F., Korablev, O., Soret, L., Gorivov, D., Belyaev, D. and Bertuax, J-L. (2025), Night O₂ (a¹D_g) airglow spatial distribution and temporal behavior on Venus based on PSICAv IR/Vex nadir dataset, Icarus, Vol. 429, 116417

How to cite: Royer, E., Avina, S., Young, E., Bullock, M., and Navarro, T.: Long-Term Ground-Based Monitoring of the Venusian O₂ Nightglow, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-356, https://doi.org/10.5194/epsc-dps2025-356, 2025.

•  The zonal winds associated with the superrotation are found to vary in many ways. There exists hemispheric asymmetry across the equator, and it varies with time. On average, the superrotation in the southern hemisphere was faster over the observational period, but it reverted sometimes.
•  Earlier studies sought periodic variabilities on the order of hundred days or decades (e.g., Kouyama et al. 2013, Khatuntsev et al. 2013, 2022), which can result from periodical forcings. However, mean zonal winds representing the superrotation exhibited broad low-frequency variability with spectra resembling the red noise spectra (Fig. 1). This is indicative of the presence of internal variability rather than responses to periodical external forcing, indicating needs for paradigm shift.
•  Long-term variability over the Venus Express and Akatsuki periods until 2020 appears that the superrotation was accelerated gradually and maximized during the Venus Express period and was then decelerated during the Akatsuki period. However, in 2021, it appears that the superrotation started fluctuating more rapidly and abruptly (Fig. 2).
•  Earlier studies found planetary-scale wave with zonal-wavenumber 1 at periods around 4 and 5 days, which were interpreted as equatorial Kelvin and Rossby waves, respectively. We found that the two waves coexist. While the ~5-day waves have nearly constant frequencies, the ~4-day waves have variable phase speeds that follow the superrotation speed. This finding provides insight on their origins, that the ~5-day waves are likely to extend over a large depth below the cloud top and that the ~4-day waves are likely to be confined near the cloud top. It further provides implications on their excitation mechanism.
•  The presence of wind variability at periods of 10 to 15 days is suggested for the first time.
•  Wind distribution of the thermal tides at around the cloud top was quantified better than in previous studies.
•  The variability in winds obtained in this study and the variability in constituents in previous studies are compared.

How to cite: Horinouchi, T., Kouyama, T., Imai, M., Murakami, S., Lee, Y. J., Yamazaki, A., Yamada, M., Watanabe, S., Imamura, T., Peralta, J., and Satoh, T.: Long-Term Variability of Mean Winds and Planetary-scale Waves around Venusian Cloud Top Observed with Akatsuki/UVI, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-255, https://doi.org/10.5194/epsc-dps2025-255, 2025.

Venus exhibits strong and changing contrasts at ultraviolet wavelengths apparently related to the clouds and the dynamics in the cloud layer, but to date their origin continues to be unknown.

In this work we analyse the possibility of correlation between the UV-brightness and the temperature structure in the atmosphere using unique data from Venus Express. On the one hand these data are measurements of the temperature structure from radio occultation data (VeRa experiment) in very small areas on Venus, on the other hand they are UV-images of the same spot up to 11 hours before and a few hours after the radio occultation experiment (VMC instrument). This type of analysis has not been presented before, as no such data exists from earlier missions.

(Three images each two hours apart taking during ingress of orbit 2805 on 25 December 2013. The yellow star indicates the spot of the VeRa radio occultation that happens after 8h, 6h and 4h respectively (left to right) of the moment of the image. The red rectangles are the wind-advected latitude / longitude boxes corresponding to VeRa location advected by the zonal and meridional winds. The boundaries of the boxes are measures of the uncertainties in the zonal and meridional winds.)

The South Polar Dynamics Campaign that was done during the last month of 2013 focussed on getting images and radio occultations on each VEX orbit. In addition, we found other orbits where this occurred. In total we identified 56 orbit with suitable data for this study. We apply a phase angle correction to compensate for the changing viewing geometry between the individual images and account for the advection of clouds by zonal and meridional winds.

(Spearman’s rank correlation coefficients for UV Radiance Factor Ratio as a function of temperature (left column) and normalised temperature (right column), at levels between 65 and 75 km altitude for three latitude bins. The largest effect is at the lower and higher altitudes, where the change of temperature with latitude is strongest. The corresponding one-sided p-value for each of the correlations is shown in the bottom panels. We choose a limit of p < 0.02 to claim significance, which is indicated by the green area at the bottom of the plots. Only for 67 km altitude in the uncorrected temperature and 67 and 68 km altitude in the normalised temperature correlation does the p-value drop below the limit.)

(The Radiance Factor Ratio versus temperature (left) and normalised temperature (right) at 67 km altitude. Normalisation is done relative to a linear least square fit to the temperature as a function of latitude at each level between 50 and 80 km altitude.)

After very carefully taking into account all the sources or error and uncertainty We find a possible anti-correlation between UV-brightness and atmospheric temperature around 67 km altitude for low latitudes, with a one percent probability this finding is due to chance (p-value= 0.01). Heating in this altitude and latitude region due to an increase in the UV-absorber has been predicted by radiative forcing studies (for example, Crisp 1986). If we assume the temperature difference we observe between UV-bright and UV-dark areas are due to this heating, then it is possible to compare this value to what is expected from the model heating rate calculations. The theoretical number would be on the order of 10-20 K, the measured value is on the order of 10 K, and thus is of the same order. This is encouraging, particularly given that this is observed only in the low latitude region, where solar heating would be expected to be most significant, and because the altitude range where the heating is observed also corresponds to that in Crisp’s model. This could be the first observational evidence for a direct link between UV-brightness and atmospheric temperature in the 65 - 70 km altitude region in the clouds of Venus.

How to cite: Roos-Serote, M., Wilson, C. F., MacDonald, R. J., Tellmann, S., Lee, Y. J., and Khatuntsev, I. V.: Correlation between temperature structure and UV contrasts in the clouds of Venus from Venus Express VMC and VeRa data., EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-35, https://doi.org/10.5194/epsc-dps2025-35, 2025.

Introduction

The Venus PCM (Planetary Climate Model) ^[1,2] has been using a pre-computed net exchange rate (NER) matrix formalism to calculate the infrared radiative transfer in the wavelength range, from 1.7 to 250 μm. This implementation allows the Venus PCM to compute temperature self-consistently. In this work, we present recent improvements done to the infrared radiative transfer, in order to improve the Venus PCM performances and reliability. The influence from different optical parameters on the deep atmosphere (below the clouds) temperature and layer stability has also been evaluated to help better understand the thermodynamic processes under the cloud.

Update of the opacity properties

When calculating the NER coefficients, correlated-k distribution for gas opacity, cloud opacities, and collision induced absorptions (CIA) for CO₂ and H₂O are integrated ^[3]. As the dominant gas compound, CO₂ dominates most of the energy exchange. In this work, the high-resolution spectrum data of different molecules are updated to the latest version. An up-to-date combination of empirical corrections of sub-lorentzian far-wing profiles of CO₂ is considered ^[4,5,6]. CIA have been updated to their latest measurements^[7], in particular in the key spectral region between 3 and 10 microns. The influence of this update on the energy exchange, as discussed in ^[8], will be presented.

Impact on the temperature and layers

Simulations

We use the Venus PCM in a 1-dimensional configuration, using a fixed solar input corresponding to the global average of solar radiation received by Venus, and run simulations for 2000 Venus days to reach equilibrium. The details of the opacity in the windows located from 2 to 10 microns is crucial as these spectral regions control the energy exchanges in the deep atmosphere and strongly affect the temperature profile from cloud base to surface^[8]. After the update of the CIA and CO₂ line shape, our results indicate that these windows are not opaque enough to reproduce the observed temperature profile, given the solar heating rate distribution used^[9][10], as shown in Figure 1.

Figure 1. Temperature profile applying different continuum settings (unit: cm^-1 amg^-2 , added in wavenumber from 500 cm^-1 to 3570 cm^-1, and in altitude from 30km ~ 50km) from the 1D configuration of the Venus PCM after 2000 Venus days of simulations, Haus’ table is used to get the solar input, the correlated-k distribution is calculated from the latest version high-resolution spectrum data and the newest CIA data are taken from [7].

Cloud-base temperature

The temperature at the cloud base is slightly under-estimated in our simulations. It mostly depends on the amount of solar energy absorbed in the middle cloud and below, as this energy is balanced by thermal emission mostly to space in the 10-30 micron spectral region at the top of the convective layer (interface between upper and middle cloud).

Temperature profile in the stable layer below the cloud base

With the obtained shape of the opacity in the 2-10 micron spectra region, energy exchanges between lower layers and the cloud base are too efficient in the stable layer (30-50 km), leading to under-estimated temperatures in the deep atmosphere. Some tests are done to evaluate the impact of additional continuum added to slightly close these windows (3-10 microns) on the temperature below the cloud. This additional continuum might be related to the lower haze, so we apply it from 30 to 50 km only. This hypothesis remains to be more fully assessed. The impact of this additional continuum is illustrated in Figure 1. In our results, this additional opacity seems to be also needed below 30 km to reach the observed T profile.

Comparison with the radiative transfer model developed at CPS (Japan) by Takahashi et al ^[11][12][13] is also done. Differences may be explained by several factors, but here we illustrate the comparison in Figure 2 by comparing extinction coefficients obtained in their work at 5x10⁶ Pa with the extinction computed at the same level in our work.

Figure 2. The absorption coefficient of the CPS radiative transfer model (adapted from figure 11 of [12]), compared with the one obtained in the Venus PCM, both at the 5x10⁶ Pa level (roughly 10 km altitude).

References

[1] Lebonnois, S., Sugimoto, N., & Gilli, G. (2016). Icarus, 278, 38-51, doi : 10.1016/j.icarus.2016.06.004

[2] Garate-Lopez, I., & Lebonnois, S. (2018). Icarus, 314, 1-11, doi : 10.1016/j.icarus.2018.05.011

[3] Eymet, V., Fournier, R., Dufresne, J. L., Lebonnois, S., Hourdin, F., & Bullock, M. A. (2009). Journal of Geophysical Research: Planets, 114(E11), doi : 10.1029/2008JE003276

[4] Tran, H., Boulet, C., Stefani, S., Snels, M., & Piccioni, G. (2011). Journal of Quantitative Spectroscopy and Radiative Transfer, 112(6), 925-936, doi : 10.1016/j.jqsrt.2010.11.021

[5] Tonkov, M. V., Filippov, N. N., Bertsev, V. V., Bouanich, J. P., Van-Thanh, N., Brodbeck, C., ... & Le Doucen, R. (1996). Applied optics, 35(24), 4863-4870.

[6] Pollack, J. B., Dalton, J. B., Grinspoon, D., Wattson, R. B., Freedman, R., Crisp, D., ... & Tipping, R. (1993). Icarus, 103(1), 1-42, doi : 10.1006/icar.1993.1055

[7] Tran, H., Hartmann, J. M., Rambinison, E. & Turbet, M. (2024). Icarus 422, 116265, doi: 10.1016/j.icarus.2024.116265

[8] Lebonnois, S., Eymet, V., Lee, C., & Vatant d'Ollone, J. (2015). Journal of Geophysical Research: Planets, 120(6), 1186-1200, doi :  10.1002/2015JE004794

[9] Haus R, Kappel D, Arnold G.(2015). Planetary and Space Science, 117:262-294. doi:10.1016/j.pss.2015.06.024

[10] Garate-Lopez I, Lebonnois S. (2018) . Icarus;314:1-11. doi:10.1016/j.icarus.2018.05.011

[11] Takahashi, Y. O., Hayashi, Y.-Y., Hashimoto, G. L., Kuramoto, K. & Ishiwatari, M. (2023). Journal of the Meteorological Society of Japan 101, 39–66, doi: 10.2151/jmsj.2023-003.

[12] Takahashi, Y. O. et al. (2024). Journal of the Meteorological Society of Japan, 102, 469–483, doi: 10.2151/jmsj.2024-025.

[13] Our team would like to express our deep sorrow, as Yoshiyuki O Takahashi passed away on April 30^th, this year.

How to cite: Han, P. and Lebonnois, S.: Effect of the different opacity factors on deep atmosphere temperature and layers in the Venus PCM, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-591, https://doi.org/10.5194/epsc-dps2025-591, 2025.

Background

The cloud layer of Venus, composed of sulfuric‑acid aerosols, plays a key role in controlling the solar energy input of the atmosphere through its effect on planetary albedo. To clarify the sequence of processes whereby sulfur dioxide (SO₂), the chemical precursor of the clouds, is transported to the cloud‑top region and photochemically converted to sulfuric acid, it is essential to understand the detailed temporal and spatial distribution of SO₂ in detail. Observations have been conducted with both ground‑based telescopes [1] and spacecraft [2, 3]; however, these measurements are spatially sparse and temporally sporadic. As a result, the relationship between SO₂ variability and atmospheric activities, as well as the evaluation of sulfur cycle and cloud formation scenarios, remains unresolved. The ultraviolet imager (UVI) onboard the Japanese Venus orbiter Akatsuki [4, 5] captures full‑disk images of Venus in two narrowband filters: 283 nm, centered on a SO₂ absorption band, and 365 nm, where absorption by an unidentified UV absorber dominates. UVI acquires nearly simultaneous two‑wavelength disk-resolved images every two hours, and its temporal and spatial resolution offers the potential to relate the variation of SO₂ and atmospheric dynamics from planetary‑scale waves down to mesoscale phenomena. However, the absorptions of SO₂ and the unidentified absorber are mixed in these two‑wavelength images, making it difficult to analyze the detailed variation of SO₂ so far. In this study, we separated the absorption contributions of SO₂ and the unidentified absorber.

Dataset and Retrieval methods

In this study, we analyzed over 15,000 pairs of 283 and 365 nm UV images taken by Akatsuki/UVI. These UV images are Level 3b data products, which are calibrated radiance maps in the longitude-latitude coordinate (0.125 degree grid). To reduce computational cost, the data were spatially binned to a resolution of 1 degree. We compared the observed reflectance distributions at 283 and 365 nm with simulated reflectance generated by the radiative transfer calculations, and drive the best-fitted pair of the mixing ratio of SO₂ and the imaginary part of the cloud refractive index (n_i) as a proxy of the unidentified absorber by an iterative algorithm. Additionally, we performed sensitivity tests to examine the effects of cloud altitude and wavelength dependence of ni on the retrieved results.

Results

We first composited all the data from 2015 to 2022 and found that the SO₂ mixing ratio peaks at the equator, decreases toward mid-latitudes, and exhibits a local maximum at 14–15 h local time. We interpret this distribution as a result of the equatorial upwelling in the Hadley-type meridional circulation and vertical movement caused by thermal tides with wavenumber 2, which lifts SO₂-rich air from the lower altitudes to the cloud top. This pattern is consistent with the results of a general circulation model coupled with photochemistry [6] and previous Venus Express/SPICAV-UV observations [3], at least with respect to latitude.

The longitude-time Hovmöller diagram (Figure 1) shows a consistent feature that moves with a period of 4 days, suggesting the dynamical influence of the Kelvin wave. On a multi-year time scale, the mean SO₂ mixing ratio increased from 2016 to 2019 and decreased by 2022 (Figure 2), in agreement with ground-based infrared observations [1]. The long-term variations of the unidentified absorber show a similar trend to those of SO₂. These variations are also correlated with changes in the mean zonal wind derived from Akatsuki cloud tracking data [7]. Because the effect of absorption by the unidentified absorber extends into the visible wavelengths where solar irradiance is strong [8], these variations suggest that enhanced solar heating may intensify thermal tides, leading to dynamical feedback that further amplifies wind speeds and further enhances SO₂ transport.

In this presentation, we highlight these newly analyzed variations across multiple temporal and spatial scales.

Figure 1: Hovmöller diagram of SO₂ mixing ratio from Feburuary 22 to Jun 2, 2018.

Figure 2: Long-term variation of the mean SO₂ mixing ratio (orange) and ni (blue) with 1-σ standard deviations (shaded). VY stands for the Venusian year from December 15, 2015

References

[1] Encrenaz T. et al., A&A, 674, A199 (2023)  

[2] Esposito LW et al., JGR-Atmospheres, 93, 5267 (1988)  

[3] Marcq E. et al., Icarus, 335, 113368 (2020)  

[4] Nakamura M. et al., Earth Planet. Space, 68, 75 (2016)  

[5] Yamazaki A. et al., Earth Planet. Space, 70, 23 (2018)  

[6] Stolzenbach A. et al., Icarus, 395, 115447 (2023)  

[7] Horinouchi T. et al., JGR–Planets, 129, e2023JE008221 (2024)  

[8] Moroz VI et al., Sov. Phys. Usp., 28, 524 (1985)

How to cite: Iwanaka, T., Imamura, T., Aoki, S., Marcq, E., and Sagawa, H.: Multiple temporal and spatial scales variation of sulfur dioxide at the Venusian cloud-top, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1141, https://doi.org/10.5194/epsc-dps2025-1141, 2025.

Context

The VenSpec-U instrument^[1] onboard the future ESA EnVision mission, will be one of the three spectrometers of the VenSpec suite, that will study Venus’ surface and atmosphere. VenSpec-U will focus on the upper part of the atmosphere and will perform UV observations of the cloud top. It will measure the backscattered sunlight on the dayside of Venus, from which radiance factor spectra will be derived by taking the incoming solar spectral irradiance into account. The scientific objectives of VenSpec-U will regard both the chemical composition and the dynamical properties of the atmosphere. Four main elements to investigate can be derived from these science goals. The firsts are the abundance of sulphured species, including especially SO₂ and SO. These species will be identified separately thanks to the “High Resolution” (HR) channel of the instrument, that will have a spectral resolution of 0.3 nm to cover the 205-235 nm wavelength range corresponding to the common absorption band of SO₂ and SO. The third objective is to monitor the unidentified UV absorber and its spectral characteristics. To that end, the “Low Resolution” (LR) channel of the instrument will operate from 190 nm to 380 nm, with a spectral resolution of 2-5 nm. Finally, VenSpec-U will investigate the small scale spatial variability of the cloud-top, by performing observations with a pushbroom observation strategy that allows the acquisition of images, at spatial samplings ranging from 3 to 24 km.

Objective and method

This study is focused on the imaging capabilities of VenSpec-U, in order to estimate the performances of the instrument for the retrieval of the small scale spatial features of Venus’ atmosphere, such as convection cells and atmospheric wave patterns. To do so, several numerical models are combined in order to simulate images as produced by VenSpec-U. The whole acquisition process aims to be modelled, from the observed scene at the cloud-top of Venus, to the consideration of the instrument’s behaviour inducing degradations of the images and spectra. The simulation of the observed scene is based on a mesoscale model of Venus’ atmosphere^[2], from which maps of the key parameters that aimed to be monitored by VenSpec-U are derived, and radiance factor spectra are generated using a radiative transfer model adapted to the instrument’s wavelength range^[3]. An instrumental model has then been developed in order to simulate the formation of images, by following successively the main steps occurring in the process, including the effects of optical components and detector as well as the main onboard data processing operations. A simple inversion algorithm is then applied. This latter is based on the simulation of a solar observation, which is foreseen for the inflight calibration of VenSpec-U, coupled to the inverse radiative transfer model that allow to process the degraded spectra to retrieve the maps of atmospheric parameters. These maps can then be compared to the initial maps used as inputs of the model binned to match the targeted spatial sampling (Fig. 1).

By modifying the amplitude of the spatial features on the initial maps, detection threshold for each parameter can be estimated so that the compliance with the targeted performances in terms of small scale variability imaging can be assessed (Fig. 2). This study has been performed for optimal observation conditions, but could however be repeated for various configurations in order to estimate their impact on the resulting detection thresholds and global performances of VenSpec-U as an imager.

Figure 1: Comparison between initial (top) and retrieved maps (bottom) of the three atmospheric parameters targeted by the LR channel: SO₂ mixing ratio (left), UV absorber imaginary refractive index (center), cloud-top control altitude (right)

Figure 2: Evolution of the correlation between the initial and retrieved maps of the four atmospheric parameters targeted by VenSpec-U: SO₂ mixing ratio (top left), UV absorber imaginary refractive index (top right), cloud-top control altitude (bottom left), SO/SO₂ abundance ratio (bottom right)

References

[1] Emmanuel Marcq, Franck Montmessin, Jérémie Lasue, Bruno Bézard, Kandis L. Jessup, et al.. Instrumental requirements for the study of Venus’ cloud top using the UV imaging spectrometer VeSUV. Advances in Space Research, 2021, 68 (1), pp.275-291. ⟨10.1016/j.asr.2021.03.012⟩. ⟨insu-03179739⟩

[2] Lefèvre, M., Lefèvre, F., Marcq, E., Määttänen, A., Stolzenbach, A., & Streel, N. (2024). Impact of the turbulent vertical mixing on chemical and cloud species in the Venus cloud layer. Geophysical Research Letters, 51, e2024GL108771. https://doi.org/10.1029/2024GL108771

[3] Lucile Conan, Emmanuel Marcq, Benjamin Lustrement, Nicolas Rouanet, Léna Parc, et al.. The VenSpec-U spectrometer onboard EnVision: sensitivity studies. Infrared Remote Sensing and Instrumentation XXXII. Proceedings SPIE 13144, Aug 2024, San Diego, United States. 43 p., ⟨10.1117/12.3027500⟩. ⟨insu-04733439⟩

How to cite: Conan, L., Marcq, E., Lustrement, B., Lefèvre, M., Rouanet, N., Leduc, B., Diaz Damian, A., Baggio, L., Bertran, S., Robert, S., Barraud, O., and Alemanno, G.: Observability of small scale atmospheric spatial variability by the VenSpec-U instrument onboard EnVision, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1481, https://doi.org/10.5194/epsc-dps2025-1481, 2025.

We have developed the Venusian general circulation model (GCM) named AFES-Venus (Atmospheric GCM for the Earth Simulator for Venus) [1, 2] and the data assimilation system based on the Local Ensemble Transform Kalman Filter (LETKF) named ALEDAS-V (AFES-LETKF data assimilation system for Venus) [3]. Here, we will introduce recent improvements of AFES-Venus and ALEDAS-V and newly obtained results.

So far, AFES-Venus reproduced the cold collar in the polar region [4], the planetary-scale streak structure observed by Akatsuki infrared (IR2) camera [5], a fully developed super-rotation [6], and spontaneous gravity waves radiated from the thermal tides [7]. The thermal tides [8] and the planetary-scale short periods (Kelvin and Rossby) waves [9, 10] consistent with observations were also reproduced by improving the profiles of static stability and solar heating. Dependency of the super-rotation on the magnitude of horizontal hyper diffusion was investigated with medium- and high-resolution simulations [11]. Recently we have implemented radiative and cloud microphysical processes into AFES-Venus (Fig.1). We have also investigated disturbances [12] and energy cycles [13] in the Venus atmosphere using Bred vectors.

ALEDAS-V improved the horizontal structures of thermal tides with the data assimilation of horizontal winds derived by cloud tracking of ultra-violet images (UVI) from Venus Express [14] and Akatsuki [15]. Although the observed horizontal winds are limited to low latitudes on the day side, the zonal-mean zonal winds and temperature were also modified globally [15]. The first analysis data in which horizontal winds obtained by Akatsuki UVI are assimilated will be released soon. The cold collar was also realistically reproduced in the analysis data [16]. We have also conducted several observing system simulation experiments (OSSEs) assuming Akatsuki Longwave Infrared Camera (LIR) observations [17]. Now we are trying to assimilate temperature obtained by Akatsuki LIR.

Fig.1: Zonal mean zonal wind [m s−1] (contours) and static stability [K km−1] (shading) for the original AFES-Venus (left: EXP-DYN) and that with a new radiative transfer process (EXP-RAD).

References: [1] Sugimoto+2014 JGR-Planets, 119, 1950–1968. [2] Sugimoto+2014 GRL, 41, 7461–7467. [3] Sugimoto+2017 Sci. Rep.. 7, 9321. [4] Ando+2016 Nature Comm., 7, 10398. [5] Kashimura+2019 Nature Comm., 10, 23. [6] Sugimoto+2019 GRL, 46, 1776–1784. [7] Sugimoto N+2021 Nature Comm., 12, 3682. [8] Suzuki+2022 JGR-Planets, 127, 7243. [9] Takagi+2022 JGR-Planets, 127, 7164. [10] Takagi+2023, JGR-Planets, 128, 7922. [11] Sugimoto+2023 Earth, Planets and Space, 75, 44. [12] Liang+2024 JGR-Planets, 129, 8067. [13] Liang+2025 GRL, 52, 112663. [14] Sugimoto+2019 GRL, 46, 4573–4580. [15] Fujisawa+2022 Sci. Rep., 12, 14577. [16] Ando+2023 JGR-Planets, 128, 7689. [17] Sugimoto+2022 Geoscience Lett., 9, 44.

How to cite: Sugimoto, N., Fujisawa, Y., Komori, N., Ando, H., Takagi, M., Kuwayama, S., Matsushima, T., Kashimura, H., Liang, J., and Miyoshi, T. and the AFES-Venus and ALEDAS-V teams: Recent improvements of general circulation model (AFES-Venus) and data assimilation system (ALEDAS-V) for the Venus Atmosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-4, https://doi.org/10.5194/epsc-dps2025-4, 2025.

Because of its rotation period of 243 days, Venus is considered a slowly rotating planet. However, its persistent superrotating atmospheric jets, which increase in speed from surface to cloud tops, effectively set a faster rotation speed than the surface rotation. Using the Venus Planetary Climate Model and wind measurements taken by the Pioneer Venus entry probes, we show that the Rossby radius of deformation of the atmosphere varies with height. The atmosphere falls into three circulation regimes: (1) from the surface to 20 km, the Rossby radius of deformation exceeds the planetary radius and no Rossby waves form; (2) from 20 to 50 km, the tropical Rossby radius becomes smaller than the planetary radius, and a circulation regime characterized by a superrotating equatorial jet and mid-latitude Rossby gyres appears; (3) from 50 to 70 km, the extratropical Rossby radius becomes smaller than the planetary radius, the jet develops mid-latitude maxima, and the Rossby gyres shift to high latitudes. Studies of exoplanetary circulation regimes as a function of rotation period have repeatedly shown a similar progression. While observing the circulations of exoplanets to confirm these predictions is not currently possible, the presence of different circulation regimes on Venus and their dependence on altitude could be tested by observing campaigns. Such evidence would be the first observational support for the theory connecting differences in planetary rotation periods to circulation regime transitions and would ground predictions of exoplanet circulations in a validated framework.

Figure 1: Horizontal and vertical winds (left column) and wave structure (right column) of the general circulation of the Venus atmosphere in a simulation by the Venus Planetary Climate Model.

How to cite: Cohen, M., Holmes, J., Lewis, S., Patel, M., and Lebonnois, S.: Three Worlds in One: Venus as a Natural Laboratory for the Effect of Rotation Period on Atmospheric Circulation, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-153, https://doi.org/10.5194/epsc-dps2025-153, 2025.

Amidst the planets of our Solar System, Venus remains one of the most intriguing subjects of scientific interest. Despite its many similarities with our home planet Earth, the evolution of this planet followed a path that resulted in a world vastly different from its neighbouring planet. Among the well-known characteristics that make Venus so unique, such as the slow rotation rate or the extreme surface temperature, its atmosphere is, without a doubt, one of the most striking. The Venusian atmosphere is a dense and inhospitable mixture primarily composed of carbon dioxide, with thick clouds of sulfuric acid. It also exhibits superrotation, where winds move much faster than the planet's rotation. To fully understand the dynamics of Venus clouds, the study of atmospheric gravity waves is a crucial step.

Atmospheric gravity waves are periodic oscillatory disturbances driven by buoyancy which are critical components in the global circulation of planetary atmospheres. These waves, which require a stably stratified atmosphere to propagate, facilitate the transfer of energy, momentum, and chemical species, significantly impacting weather systems. On Venus, atmospheric gravity waves play an essential role in the dynamics of its atmosphere. Despite previous studies that have mapped the presence of these waves in various wavelengths across Venus's cloud deck, many aspects remain poorly understood, particularly their role in driving the planet’s superrotation.

This work leverages observations from Akatsuki’s Ultraviolet Imager (UVI) to explore wave-like structures on the dayside of Venus's atmosphere at a wavelength of 365 nm. By analyzing data from Akatsuki’s public database, we aim to characterize the population of atmospheric gravity waves, measuring their physical properties (e.g., crest number, horizontal wavelength, packet length, width, and orientation) and dynamical characteristics such as the intrinsic phase velocity and vertical wavelength). Additionally, we will investigate the local time dependence and oscillation frequencies of these waves to understand their excitation sources, including atmospheric convection. This research builds on previous studies by Peralta et al. (2008), Silva et al. (2021) and Silva et al. (2024), advancing our understanding of Venus’s atmosphere and the mechanisms underlying its dynamics.

[1] Peralta et al., Characterization of mesoscale gravity waves in the upper and lower clouds of venus from vex-virtis images. Journal of Geophysical Research: Planets, 113(E5), 2008.
[2] Piccialli et al., High latitude gravity waves at the venus cloud tops as observed by the venus monitoring camera on board venus express. Icarus, 227:94 111, 01 2014.
[3] Silva et al., Characterising atmospheric gravity waves on the nightside lower clouds of Venus: a systematic analysis, AA 649 A34, 2021.
[4] Silva et al., Atmospheric gravity waves in Venus dayside clouds from VIRTIS-M images, Icarus, Volume 415, 2024, 116076, ISSN 0019-1035.

Acknowledgements: This work was supported by the Portuguese Fundação Para a Ciência e a Tecnologia of reference PTDC/FIS-AST/29942/2017, through national funds and by FEDER through COMPETE 2020 of reference POCI-01-0145-FEDER-007672, and through a grant of reference 2020.06389.BD.

How to cite: Espadinha, D., Machado, P., Peralta, J., Silva, J., and Brasil, F.: Morphological and dynamical characterisation of Gravity Waves on Venus’ atmosphere using Akatsuki´s UVI instrument, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-964, https://doi.org/10.5194/epsc-dps2025-964, 2025.

Planetary-scale waves are expected to be crucial in driving the Venusian planetary-scale atmospheric circulation. To understand the interaction between the waves and the mean flow, we obtained temporal frequency spectra of the cloud-top brightness temperature using thermal infrared images taken by the Longwave Infrared Camera (LIR) onboard Akatsuki over a period of 10 Venus years. Waves in the equatorial region with periods of around 3.5–4.3 days were identified as Kelvin waves, while waves in the mid-latitude with periods of about 5.0–6.0 were identified as Rossby waves. The mid-latitude waves with periods 5.0–6.0 days tend to accompany additional local amplitude maxima near the equator, especially when observed at small emission angles. Considering the contribution function of LIR extends to lower altitudes for smaller emission angles, the result implies the waves arise from Rossby-Kelvin instability and the associated Kelvin modes reside below the cloud top. Mid-latitude peaks are also sometimes seen around periods of 3.5–4.0 days and coupled with equatorial modes, indicative of Rossby-Kelvin instability. The periods and amplitudes of the waves change with time, and the variations seem to correlate with the background wind in such a way that waves with small intrinsic frequencies are less prominent.

Figure: Latitudinal distributions of the wave amplitudes at the period of (a) 5.04 days and (b) 3.71 days for the emission angle ranges of 30–40 (blue solid), 40–50 (orange dashed), and 50–60 (green dotted). 

How to cite: Imamura, T., Koyama, H., Sato, T. M., Kouyama, T., and Taguchi, M.: Venusian planetary-scale waves observed by Akatsuki LIR: Rossby-Kelvin instability and long-term variation, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-682, https://doi.org/10.5194/epsc-dps2025-682, 2025.

The vertical structure of the thermal tide in the Venusian low-latitude region (0˚-30˚ latitudes) was investigated by the Akatsuki radio occultation measurements. The result shows that the phase of the diurnal tide little varies in the vertical direction, while that of the semidiurnal tide tilts toward earlier local times with increasing altitude above 65 km and tilts in the same direction with decreasing altitude below 50 km. This indicates that the semidiurnal tide is excited between 50 and 65 km altitudes and propagates upward above these heights and downward below. The vertical momentum flux associated with the semidiurnal tide in low latitudes was calculated above 58 km, and the associated acceleration rate near the cloud top was estimated. As a result, the estimated accleration rate was comparable to those expected in the previous numerical studies. Our results observationally confirmed the simultaneous upward and downward propagations of the thermal tide, which can account for the vertical shear of the Venusian atmospheric superrotation in low latitudes, supporting the previous theoretical predictions.

How to cite: Ando, H., Noguchi, K., Imamura, T., Takagi, M., Sugimoto, N., Matsuda, Y., Tellmann, S., Pätzold, M., Häusler, B., Choudhary, R., and Antonita, M.: Vertical propagation of Venusian thermal tides above and below clouds investigated by Akatsuki radio occultation, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-163, https://doi.org/10.5194/epsc-dps2025-163, 2025.

Observations of solar light backscattered by Venus' cloud top in the ultraviolet domain carry a rich scientific content, since they can be used to monitor absorbing species column densities, namely trace species like SO₂ and SO[1,2], but also the well-mixed main constituent CO₂ (which helps in constraining cloud top altitude) as well as the infamous UV absorber whose composition is still unknown as of 2025. These observations have revealed a large spatial and temporal variability at various scales, whose origin is still debated (atmospheric oscillations and/or volcanic plume forcings?)

Data analysis was usually performed using plane-parallel or pseudo-spherical radiative transfer models based on publicly available codes such as e.g. DISORT[3]. However, applying such models was not relevant at high emission or solar zenith angles (e.g. near dusk or dawn, or at very high latitudes), nor at very small horizontal scales comparable to the photon free mean path between two scattering events. To circumvent these limits, we used a 3D Monte Carlo solver provided by the MesoStar> company, and previously used to study Titan's atmosphere[4].

Preliminary results show that:

• 1D pseudo-spherical and spherical Monte-Carlo models agree for nadir observations up to solar zenith angles as high as 75°;
• Analysis of SPICAV-UV/Venus Express data near the terminator exhibit a already known decrease in SO₂ with increasing latitude, as well as dusk/dawn asymmetry in SO₂ column density (to be further investigated and confirmed);
• Horizontal UV contrasts at Venus' cloud top are typically blurred over a typical scale of ~10 km due to multiple scattering in the horizontal direction by the upper haze.

This work has been funded by the French National Research Agency (ANR), project RaD3-net, grant number ANR-21-CE49-0020-01.

References
[1] Marcq et al., Icarus (2020)
[2] Marcq et al., Nat Geosci (2013)
[3] Laszlo et al., in Light Scattering reviews (2016)
[4] He et al., JQSRT (2025, accepted)

How to cite: Salugová, E., Marcq, E., He, Z., and Vinatier, S.: 3D Monte-Carlo modeling of Venus' reflectance in UV, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-403, https://doi.org/10.5194/epsc-dps2025-403, 2025.

Venus’s atmosphere is characterized by pronounced thermal tides, which have been extensively studied at the cloud level through direct observations and numerical simulations. There, a semi-diurnal tide dominates the equatorial region and a diurnal signal is more prominent at high latitudes. Due to the lack of measurements at the lower levels of the atmosphere, less attention has been given to the significance of the thermal forcing close to the surface. However, understanding the surface thermal tide has significant implications for Venus's atmospheric dynamics, and for future exploration of Venus's atmosphere, for example, via the effect of the surface pressure variations on the atmospheric loading on the gravity field.
Using idealized simulations from a Venus PCM - LMDZ (Lebonnois et al. 2010), we examine surface thermal tides and planetary-scale wave activity in the lower atmosphere, a region that remains largely unconstrained by direct observations. The analysis focuses on the surface pressure anomalies induced by solar forcing, which exhibit a systematic phase lag relative to the sub-solar point. 
Here we find that the phase lag’s dependence on solar day length across simulations reveals a consistent radiative timescale governing the thermal response of the near-surface atmosphere.
As the solar day shortens, the pressure response transitions from a predominantly diurnal to a semi-diurnal structure, suggesting a resonance between the forcing frequency and the thermal response of the lower atmosphere. In addition to the tidal signal, a large-scale wave mode emerges in the simulations, confined vertically below the cloud layer around 15 km altitude. This wave displays properties consistent with an internal gravity wave, including westward propagation, and peak amplitude in a stably stratified layer. Its period remains largely insensitive to the imposed solar day, suggesting it is governed by intrinsic atmospheric structure rather than external forcing.

How to cite: Navon, R., Galanti, E., and Kaspi, Y.: The phase of Venus’s surface thermal tide simulated with a Venus PCM, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-596, https://doi.org/10.5194/epsc-dps2025-596, 2025.

Atmospheric waves are present in the Venus atmosphere across a wide range of spatial scales and may play a significant role in the planet's energy and momentum budget. Small-scale temperature fluctuations, likely caused by gravity waves, are a common feature in the atmospheres of all planets. These gravity waves play a crucial role in redistributing energy and momentum within the atmosphere. Several instruments have detected gravity waves in the Venusian mesosphere and upper cloud region, but their role in maintaining the atmospheric superrotation is not yet fully understood.

From 2006 to 2014, the Venus Express Radio Science Experiment (VeRa) investigated the neutral atmosphere and ionosphere of Venus in Earth occultation geometry using the spacecraft's radio subsystem at two coherent frequencies, X-band (8.4 GHz) and S-band (2.3 GHz). Radial profiles of neutral number density, derived from altitudes between 40 and 90 km, are then converted into vertical profiles of temperature and pressure, assuming hydrostatic equilibrium.

VeRa atmospheric profiles in the upper troposphere and mesosphere show high variability due to atmospheric waves and turbulence. Small-scale temperature fluctuations originating from internal gravity waves with vertical wavelengths of only a few kilometers are detectable in the VeRa profiles.

The high vertical resolution of VeRa’s temperature profiles offers a unique opportunity to study small vertical temperature fluctuations that would otherwise be unobservable by any other remote sensing technique. These studies are crucial for understanding Venus's poorly constrained energy and momentum budgets.

The observed wave structures are analyzed using standard wave theory to investigate their vertical and horizontal structure as a function of latitude, altitude, and local time.

How to cite: Tellmann, S., Pätzold, M., and Oschlisniok, J.: Small-Scale Gravity Waves in the Venus Atmosphere as seen by the VeRa Experiment on Venus Express, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-624, https://doi.org/10.5194/epsc-dps2025-624, 2025.

Venus is a planet that has garnered renewed interest in recent years. Regarded as Earth’s twin, as it shares many of its basic properties with our home in the Solar System. However, upon close inspection, similarities between the two planets end, whose present conditions in contrast to Earth expose how different the evolution of Venus must have been. Many unanswered questions remain regarding the process that led to Venus’ current conditions, which have motivated at least one future space mission towards the planet in the 2030’s, EnVision. In the meantime, it continues to be an exciting target for new discoveries as we try to peer deeper into our neighbouring planet.

The atmosphere of Venus is on such subject of continuous research, with a thick layer of clouds speeding around the globe in approximately four days in its uppermost regions. Approximately 90 times as massive as Earth and mostly composed of carbon dioxide, its lower troposphere and near-surface conditions are extremely challenging to access with remote observations. However, processes that are observable in the cloud layer between roughly 50-70 km of altitude manifest a tentative connection to the surface. One of these is the presence of stationary features which seem correlated with prevalent topography on the surface.

In the past decade, bow-shaped stationary features jumped to the spotlight with the observation of a planetary scale feature by the Japanese space mission Akatsuki in December 2015 [Fukuhara et al. 2017]. Further detections by ESA’s Venus Express mission between 2006-2008 [Peralta et al. 2017] reinforced these findings. Several instruments onboard Akatsuki have thus far provided a continuous cover of the planet’s cloud layer, including further detection and characterization of stationary features on the top of the clouds with the Ultraviolet Imager (UVI) [Kitahara et al. 2019] which is sensitive to ultraviolet radiation, and at slightly lower levels thanks to the capabilities of the Longwave Infrared Camera (LIR) [Fukuya et al. 2022] which senses the thermal emission from the upper clouds at mid-infrared. Such features have also been reported using the IR2 camera [Sato et al. 2020], using dayside observations at 2.02 microns sensitive to one of the CO2 absorption bands. Most of these features have been interpreted as a form of atmospheric gravity wave, in this case generated by flow over prominent topography.

Gravity waves are periodic perturbations in which the buoyancy of the perturbed fluid acts as the restoring force. These waves require a forcing mechanism to be generated, and a statically stable environment so that they can propagate through the fluid in which they are generated. Given that their properties allow them to carry energy and momentum across the atmosphere, especially in the vertical direction, they become a crucial subject matter for atmospheric science. For the case of Venus, they represent a good opportunity to investigate the conditions in which objects like stationary waves might form, and if they are of orographic origin. As they are observed in the cloud layer of Venus, which for dayside visible and mid-infrared observations usually represents a region between 60-70 km of altitude, they may establish a link between the cloud layer and the surface. However, a positive static stability environment, which is necessary for the propagation of these waves, does not seem to always be verified between the surface and the cloud layer. There lies the puzzle of explaining the existence of such phenomena in the cloud layer, although considerable efforts have already been directed in this front with some success, through atmospheric modeling [Imamura et al. 2018, Lefèvre et al. 2020]. Several of these efforts mention the need for extended observations of these features for a more robust interpretation of the generation and propagation of stationary waves on Venus.

We present here a contribution in this front, taking advantage of data from multiple instruments to detect and characterise stationary features which resemble gravity waves on the dayside of Venus. We used data from the VIRTIS instrument onboard the Venus Express mission, using multiple wavelengths that can detect contrasting features in the clouds at several levels of the cloud layer. To complement this selection, we used data from the IR2 instrument with the 2.02 micron filter, following up on previous observations and performed a reanalysis of the structures reported in Kitahara et al. (2019) detected most strongly at 283 nm with the UVI instrument. To our surprise the distribution of features does not seem to be completely correlated with noteworthy topography and some exhibit morphologies that have not been documented for waves of this kind on Venus. The length scales of the new features are in the mesoscale range with horizontal wavelengths mostly between 100-200 km, and whose properties are in good agreement with previous studies of this phenomena on Venus, albeit with an arguably more diverse range of shapes and a wider geographical distribution and local time.

References

Fukuhara et al. 2017, Nat. Geoscience; DOI: 10.1038/NGEO2873

Fukuya et al. 2022, Icarus; DOI: 10.1016/j.icarus.2022.114936

Imamura et al. 2018, JGR Planets; DOI: 10.1029/2018JE005627

Kitahara et al. 2019, JGR Planets; DOI: 10.1029/2018JE005842

Kouyama et al. 2017, Geophys. Res. Lett.; DOI: 10.1002/2017GL075792

Lefèvre et al. 2020, Icarus; DOI: 10.1016/j.icarus.2019.07.010

Peralta et al. 2017, Nat. Astronomy; DOI: 10.1038/s41550-017-0187

Sato et al. 2020, Icarus; DOI: 10.1016/j.icarus.2020.113682

How to cite: Silva, J., Peralta, J., Imamura, T., Lefèvre, M., Machado, P., Cardesín, A., Ando, H., Brasil, F., Espadinha, D., and Joo Lee, Y.: Cross-Instrument stationary features on Venus’ dayside atmosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-595, https://doi.org/10.5194/epsc-dps2025-595, 2025.

Introduction

The clouds of Venus are unique in the solar system, comprising multiple layers at an altitude ranging from 50 to 70 kilometres and enveloping the entire surface of the planet. They consist of droplets of liquid sulphuric acid (70-95% by mass) and water, exhibiting a bi- or tri-modal size distribution. It has been observed that the three modes have a radius of approximately 0.3, 1 and 2 micrometres, respectively⁽¹⁾.

Modelling these clouds represents a significant challenge in comprehending the dynamics of Venus atmosphere. However, the models that have been developed so far are mainly in 1D^(2–6), and the few 2D and 3D models are limited to simplified equilibrium schemes^(7–10). The present study focuses on the first 3D modelling of Venus clouds employing a comprehensive microphysics model, and its 1D validation. The Venus PCM^{(11, 12)}, a GCM that incorporates a comprehensive chemistry model, a radiative transfer scheme and a parametrisation of the clouds, is used in this study. The existing cloud parametrisation⁽¹⁰⁾ assumes that the clouds are in a state of constant thermodynamical equilibrium with the water vapour and sulfuric acid at each timestep.

Method

We have coupled the MAD-VenLA model from the work of Guilbon⁽¹³⁾ and Määttänen⁽¹⁴⁾ to the Venus PCM. MAD-VenLA is a modal model that describes two particle modes that have a lognormal form and a fixed standard deviation. MAD-VenLA includes a scheme of homogeneous nucleation⁽¹⁵⁾, a simplified parametrisation of heterogeneous nucleation, Brownian coagulation, condensation and evaporation⁽¹⁴⁾. In addition, MAD-VenLA incorporates mode-merging⁽¹⁶⁾ that allows transfer particles from one mode to another. The sedimentation scheme uses the Stokes terminal speed modified by the Cunningham correction.

Results

A key issue we have with the coupling of the 0D microphysical scheme and the 3D GCM is the difference between the timestep lengths (1s for 0D, 7 minutes for 3D). For ensuring stability of the calculations with the longer timestep in 3D,  we have updated the solution of the condensation/evaporation scheme with a Runge-Kutta 4 scheme. We also adapted for our purpose the state-of-the-art sedimentation scheme adapted from Stolzenbach⁽¹⁰⁾.

The goal of this study is to link a complete microphysical scheme to a state of the art GCM to reproduce realistic clouds in regards to 3D dynamical regime. Before presenting the 3D simulation results, we examine 1D simulations of several Venus Days. These tests aim to validate the behaviour of the microphysical scheme by comparing it to the observations and to other microphysical schemes (Fig 1,2).

We will present our first 3D simulations that are relatively short simulations initialized with the equilibrium state computed with the parametrisation from Stolzenbach⁽¹⁰⁾. These simulations did not yet reach the steady states but they provide a first look the both vertical and the horizontal distributions of the cloud droplets.(Fig 3.)

We are planning to run longer 3D simulations to reach a steady-state in order to compare the simulated clouds to the observations of the past missions and also give information for the upcoming ones (EnVision, etc.).

Figure 1: Droplet density profile (in droplet.cm-3) of mode 1 (in red) and mode 2 (in black)  particles at the initialization (full line) and after half a Venusian day (dashed line) with the 1D version of the Venus PCM. The outputs are compared to the Knollenberg data (crosses). Since MAD-VenLA is only composed of 2 modes, we sum up the mass of the mode 2 and mode 3 from the Knollenberg data.

Figure 2 : Mass-loading profile (in mg.m^-3) of mode 1 (in red)  and mode 2 (in blue)  particles at the initialization (full line) and after half a Venusian day (dashed line) with the 1D version of the Venus PCM. The outputs are compared to the Knollenberg data (crosses). Since MAD-VenLA is only composed of 2 modes, we sum up the mass of the mode 2 and mode 3 from the data.

Figure 3: Horizontal map of the distribution of the 3rd order moment of mode 2 droplets after 2 terrestrial days at 55 km of altitude. This map is the result of a 3D simulation with the Venus PCM with MAD-VenLA. It presents the distribution of the volume of the droplets in each pixel.

References

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• E. P. James, O. B. Toon, G. Schubert, Icarus. 129, 147–171 (1997).
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• A. Stolzenbach, F. Lefèvre, S. Lebonnois, A. Määttänen, Icarus. 395, 115447 (2023).
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How to cite: Streel, N., Määttänen, A., Lefèvre, F., and Stolzenbach, A.: Detailed microphysics coupled with the Venus Planetary Climate Model : One-dimensional and three-dimensional simulations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-97, https://doi.org/10.5194/epsc-dps2025-97, 2025.

Venus is completely shrouded by optically thick clouds of sulfuric acid that are located between ~47 and 70 km. The cloud tops have been investigated through imaging, spectroscopy, and polarimetry in a broad range of wavelengths, from UV to mid-infrared, as well as in-situ measurements. For example, Ignatiev et al. (2009) studied the cloud top altitude from the depth of CO₂ absorption band at 1.6 μm acquired by VIRTIS onboard Venus Express. They found that the cloud tops decreased poleward of 50° and this depression coincided with the eye of the polar vortex. Sato et al. (2020) described the dayside cloud top structure of Venus using the 2.02-μm channel (designed for sensing at a CO₂ absorption band) of the 2-μm camera (IR2) onboard Akatsuki. They showed that the latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45° latitude. It rapidly dropped at latitudes of 50–60° and reached 61 km in latitudes of 70–75°.

We have investigated the solar phase angle dependence of the reflected sunlight in the low-latitude region (30°S–30°N) using the complete set of 2.02-μm images. A total of 374 images taken from December 11, 2015, to October 29, 2016 were selected by carefully excluding those with saturated pixels and/or defect image tiles. In general, the reflected sunlight gets more intense as solar phase angle increases due to the forward scattering of aerosols in the atmosphere. Interestingly, the curve of the reflected sunlight in solar phase angles higher than 90° acquired in Orbit #29–30 was approximately twice more gradual than that acquired in Orbit #11–12. Because these data were taken under the similar geometry, the difference is likely to be caused by some real variations in the cloud top structure. Such solar phase angle dependence of the reflected sunlight or brightness temperature in the same region was also studied using images taken in the same observation period but at other wavelengths: 283 nm and 365 nm from the Ultraviolet imager (UVI), 0.9 μm from the 1-μm camera (IR1), and 10 μm from the Longwave infrared camera (LIR). This multispectral comparison showed that no significant difference in the curve between Orbit #11–12 and #29–30 was detected at the wavelengths other than 2.02 μm. Wavelengths at 283 nm, 365 nm, and 0.9 μm are sensitive to optical thickness of aerosols but insensitive to their vertical distributions; therefore, vertical distributions of Modes 1 and 2 particles characterized by scale height are key parameters to make the difference in the curve of the reflected sunlight discovered from the 2.02-μm images. To support this hypothesis, we selected the data to make two groups: Group 1 (including Orbit #11–12) and Group 2 (including Orbit #29–30). For each group, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the low-latitude region were used to retrieve cloud top altitude z_c and cloud scale height H by means of radiative transfer calculation. While the best-fit combination for Group 1 is obtained at (z_c, H) = (70.4 km, 5.5 km), that for Group B is found at (z_c, H) = (69.9 km, 3.5 km). The results quantitatively show that the difference can be explained by the 2-km difference of cloud scale height.

In this presentation, we present the solar phase angle dependence of the reflected sunlight or brightness temperature using the five wavelengths of Akatsuki’s instruments. The details of the radiative transfer model and fitting results are shown. Finally, we will discuss whether the best-fit models retrieved from Groups 1 and 2 are compatible with the data at other wavelengths.

How to cite: Sato, T. and Satoh, T.: Short-term variation in the dayside cloud top structure of Venus: A search for a cause using multispectral images of Akatsuki, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1290, https://doi.org/10.5194/epsc-dps2025-1290, 2025.

The measurement of isotopic ratios on Venus is crucial to track atmospheric loss though time, constrain planetary origin and trace surface-atmosphere interactions [1]. The deuterium to hydrogen ratio (D/H) is found to be 157 times greater than that of Earth's oceans [2, 3], suggesting Venus once had a larger quantity of water. The carbon and oxygen isotopic ratios, ¹²C/¹³C and ¹⁶O/¹⁸O, have been measured by the Pioneer Venus and Venera missions [4, 5], as well as through ground-based infrared spectroscopy [6, 7, 8, 9]. They are consistent with Earth’s ratios within uncertainties (¹²C/¹³C ~ 89, ¹⁶O/¹⁸O ~ 500), suggesting little escape or photochemical alteration of CO₂ through time.

We present new simultaneous measurements of bulk-averaged ratios of ¹⁶O/¹⁸O, ^¹6O/¹⁷O and ¹²C/¹³C, measured on CO₂, on Venus’ dayside, from high spectral resolution (R ~ 80 000) iSHELL/IRTF observations, using the H3 mode (1.64-1.82 µm), performed on the 2^nd February 2024. Venus angular diameter was 12.2'', with an illuminated fraction of 86.1 %. Wavelength calibration, flat fielding, dark correction and sky subtraction were performed using the Spextool data reduction software [10, 11]. Absolute flux calibration could not be performed since the SNR of our standard star was too low.

We selected spectral order 314 (1.660–1.667 µm) to estimate the ¹⁶O/¹⁸O ratio, order 316 (1.650–1.657 µm) for the ¹⁶O/¹⁷O ratio, and order 311 (1.676–1.683 µm) to determine the ¹²C/¹³C ratio. Pairs of adjacent isotopologue lines were selected, with a minimum telluric and solar contamination. Forward models were simulated using ASIMUT-ALVL [12] for a range of possible isotopic ratios (scalers 0.85-1.15). For each line pair, the line depth ratio method [7, 13, 14] was used to obtain the best fit isotopic ratio, by comparison of the measured line depth ratio with the modeled one through a simple linear interpolation.

The following preliminary weighted averaged isotopic ratios were computed: ¹⁶O/¹⁸O ~ 507 ± 50, ¹⁶O/¹⁷O ~ 2745 ± 152 and ¹²C/¹³C ~ 90 ± 6, which are consistent with previously reported values [7, 8, 9]. The main limitations of our current measurements arise from uncertainties in line intensities (approximately 5%, based on the HITRAN database), the lack of an absolute flux calibration source with sufficiently high signal-to-noise ratio and uncertainties in the assumed temperature profile in the forward modeling. Ongoing analysis of data from mode H3 (1.64-1.82 µm), and from mode K3 (2.26-2.55 µm), which covers the OCS isotopologues absorption features at 2.42-2.46 µm, will be explored to get an estimate of the ratios of ³⁵Cl/³⁷Cl and ³²S/³⁴S, respectively,  opening an opportunity to shed some light on current volcanic outgassing processes, photochemistry and sulphur cycle dynamics.

References. (1) Avice et al. 2022, Space Science Reviews (2) Donahue et al., 1997, Science (3) Bézard et al. 2007, JGR Planets (4) Hoffman et al. 1980, JGR Space Physics (5) Istomin et al. 1980, 23rd COSPAR meeting, Budapest, Hungary (6) Kuiper et al. 1962, Comm. Lunar Planet. Lab (7) Beźard et al. 1987, Icarus (8) Hedelt et al. 2011, A&A (9) Iwagami et al. 2015, Planetary and Space Science (10) Cushing et al. 2004, PASP 116 (11) Vacca et al. 2003, PASP 115 (12) Vandaele et al. 2006, ESRIN, Italy (13) Krasnopolsky et al. 2010, Icarus (14) Encrenaz et al. 2012, A&A

Funding. JAD acknowledges funding through the research grants UIDB/04434/2020 and UIDP/04434/2020 and a fellowship grant 2022.09859.BD. SR acknowledges funding by the Belgian Science Policy Office (BELSPO) with the financial and contractual coordination by the ESA Prodex Office (PEA 4000144206).

How to cite: Dias, J., Machado, P., Robert, S., Sagawa, H., Sato, T., and Aoki, S.: Measuring Isotopic Ratios on Venus’ Dayside using iSHELL/IRTF Observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-483, https://doi.org/10.5194/epsc-dps2025-483, 2025.

Understanding the composition and distribution of the unknown UV absorber (Figure 1) in the Venusian atmosphere has been an open question in planetary science for close to 100 years. Ferric chloride (FeCl₃) has been proposed as the cause of the absorption [1], but the absorption spectrum of FeCl₃ generally used in the literature was measured in ethyl acetate [2], which is not present on Venus and produces an absorption spectrum with little similarity to the Venusian absorber [3].

Figure 1: A false colour image of Venus. Regions of UV absorption appear orange. The cause of this absorption is unknown. Image credit: NASA/JPL-Caltech. 

 We have measured the absorption spectrum of FeCl₃ in sulphuric acid with small quantities of HCl added, and we found that it is much more similar in shape to the observed spectrum of the unknown absorber than prior FeCl₃ spectra available in the literature (Figure 2). 

Figure 2: Comparison of the FeCl₃ spectra in ethyl acetate [2] and sulphuric acid (this work) with a spectrum of the unknown UV absorber recorded by MASCS/MESSENGER [3].

When added to sulphuric acid, a mixture of ferric chloride and ferric sulphate ions are observed. We estimated the molar partitioning of the species in the mixtures by performing least squares fitting to reproduce each measured spectrum from spectra of pure ferric sulphate (measured for Fe₂(SO₄)₃ in 75-78 wt% aqueous H₂SO₄) and pure ferric chloride (measured for FeCl₃ in 5-37 wt% aqueous HCl).

The fraction of the observed absorption that can be reproduced by FeCl₃ was investigated using three models: the global Planetary Climate Model for Venus (PCM-Venus) to model the photochemistry and 3D transport of the candidates in the atmosphere [4], a 1D sectional aerosol model to predict agglomeration and sedimentation as a transport mechanism of FeCl₃ particles [5], and the 1D multiple scattering radiative transfer model SOCRATES [6]. 

The required concentrations of FeCl₃ in the different cloud modes to reproduce observations taken by MESSENGER/MASCS during its June 2007 Venus flyby [3] were estimated for different cloud modes using SOCRATES. The full absorption can be explained by approximately 1.5 - 2 wt% FeCl₃ in the mode 1 cloud droplets (Figure 3). Some contribution from ferric sulphate ions is also expected, but absorbs in the same wavelength region as SO₂, so its precise contribution could not be reliable constrained.

Figure 3: Comparison of MASCS/MESSENGER measured reflectance (crosses) [3] with the modelled spectrum with SO₂ only (blue line), and with 1.2 – 2.0 wt% FeCl₃ in mode 1 cloud droplets (orange and red lines).

Iron chemistry was added into PCM-Venus in order to predict the abundance of gas-phase FeCl₃ produced by the reaction of gas-phase HCl with iron produced by the ablation of cosmic dust particles around 115 km. Mean gas and dynamical profiles from the PCM were used to initialise the agglomeration and sedimentation model, which was then run for many Venus years to reach steady state. Agglomeration and sedimentation modelling of FeCl₃ suggests that the PCM-modelled FeCl₃ column abundance above 60 km can account for more than 40% of the observed absorption. The flux of meteoric iron into the Venusian atmosphere has not been measured, and may be significantly higher than assumed in this work [7].

References 

[1] Zasova et al. 1981, https://doi.org/10.1016/0273-1177(81)90213-1 

[2] Aoshima et al. 2013, http://doi.org/10.1039/C3PY00352C

[3] Pérez-Hoyos et al. 2018, https://doi.org/10.1002/2017JE005406 

[4] Martinez et al. 2024, doi.org/10.1016/j.icarus.2024.116035 

[5] Frankland et al. 2017, https://doi.org/10.1016/j.icarus.2017.06.005 

[6] Manners et al. 2022, SOCRATES Technical Guide, available at: https://code.metoffice.gov.uk/trac/socrates 

[7] Carrillo-Sánchez et al. 2020, https://doi.org/10.1016/j.icarus.2019.113395

How to cite: Egan, J., Feng, W., James, A., Manners, J., Marsh, D., and Plane, J.: Investigation of ferric chloride as the cause of the Venusian NUV absorption, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1039, https://doi.org/10.5194/epsc-dps2025-1039, 2025.

Until the ESA Venus Express mission, the Venus mesosphere was a poorly understood region of Venus’s atmosphere. This mission revealed the composition and thermal structure of the mesosphere and lower-thermosphere [1] with the help of its suite of instruments: VIRTIS [2], SPICAV-IR and SPICAV-UV [3], VeRA [4], and SOIR [5].

In particular, the SOIR instrument performed solar occultation measurements in the IR region (2.2 - 4.3 µm) at a spectral resolution of 0.12 cm^-1, among the highest of all space instruments. It combined an echelle spectrometer and an Acousto-Optical Tunable Filter for the order selection. SOIR performed more than 1500 solar occultation measurements leading to about two millions spectra [6].

Above 100 km, SOIR could derive the CO₂ and CO concentration, up to ~170 km, and, using the hydrostatic equation, the temperature could be obtained [7, 8].

Towards the end of the Venus Express mission, an aerobreaking campaign (VExADE) was conducted, making the spacecraft dive into the atmosphere down to altitudes of ~130 km [9]. This experiment used the accelerometer data to compute the total mass density by computing the forces that were measured by the spacecraft due to aerobraking .

In this work, we use the data from both the SOIR and VExADE experiments to derive the high altitude concentrations of N₂ and atomic oxygen, providing information that is not yet available for this atmospheric region. Indeed, N₂ and O are not measurable in the infrared using a spectrometer since these species do not have absorption lines in this spectral region. Moreover, from previous observations obtained by the Pioneer Venus mass spectrometer [10], N₂ and CO could not be differentiated due to their same molar masses.

We will present the results and discuss their impact on the photochemistry, CO and O being byproducts of the CO₂ photodissociation occurring in the Venus mesosphere. We will also compare our results to the ones obtained from the state-of-art Global Circulation Model (GCM) Venus Climate Database [11].

References:

[1] Limaye, S.S., et al. (2018), Space Science Reviews

[2] Drossart, P., et al. (2007), Planet. Space Sci.

[3] Bertaux, J.L., et al. (2007), Planet. Space Sci.

[4] Tellmann, S., et al. (2012), Icarus

[5] Nevejans, D., et al. (2006), Applied Optics

[6] Vandaele , A.C., et al. (2016), Adv. Space Res.

[7] Mahieux, A., et al. (2023), Icarus

[8] Mahieux, A., et al. (2015), Planet. Space Sci.

[9] Müller-Wodarg, I.C.F., et al. (2016), Nature Physics

[10] von Zahn, U., et al. (1980), J. Geophys. Res.

[11] Gilli, G., et al. (2021), Icarus

How to cite: Mahieux, A., Rosenblatt, P., Bissery, A., Robert, S., Trompet, L., Piccialli, A., and Vandaele, A. C.: Determination of the Venus upper atmosphere gas concentration combining the SOIR/Venus Express and Torque aerobreaking observations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-479, https://doi.org/10.5194/epsc-dps2025-479, 2025.

The composition and chemical processing occurring within the Venus atmosphere is derived by a combination of direct observation (both in-situ and remote) and chemical and climate modeling (Widemann et al. 2024, Marcq et al. 2018). Chemical modeling and atmospheric properties retrievals from observations are interdependent efforts. Venus’s bulk atmosphere is composed of CO₂ (96.5%) and N₂ (3.5%), while SO₂ (~0.015%), Argon (0.007%) and water (0.002%) round out the top 5 gas species present in the Venus atmosphere. Observations and chemical modeling indicate that Venus's clouds also host a myriad of sulfur, oxygen, nitrogen, hydrogen, chlorine, carbon and oxygen trace gas species. While it is understood that the Venus clouds are dominantly composed of H₂SO₄ aerosol, and that the H₂SO₄ gas within the atmosphere is formed by chain reaction of SO₂ photolysis leading to formation of SO₃ and the interaction of SO₃ with H₂O—many questions remain about what controls the abundance of H₂SO₄, H₂O and SO₂ in the Venus atmosphere (Marcq et al. 2018, Bierson et al. 2020, Rimmer et al. 2021, Dai et al. 2022). Unequivocal answers to these questions are dependent on how precisely we can identify and quantify the other trace gas and aerosol forming species present in the atmosphere and their propensity to interact with Venus’s sulfur, oxygen and water budgets.  (Mogul et al. 2021, Rimmer et al. 2021, Jiang et al. 2023, Jessup et al. 2020)

Progress in resolving these questions is being made as chemical and climate modeling become increasingly sophisticated (Stolenzbach et al. 2023, Dai et al. 2022, Dai et al. 2024). Likewise, efforts to advance and improve lab and theoretical studies of the physical properties of gases and aerosols that may be present in the Venus atmosphere are on-going (Frandsen et al. 2024, Skog et al. 2024, Jiang et al. 2023, Heays et al. 2017 Heays et al. 2023). These advances and the anticipation of several new Venus missions, motivates the review/re-analysis of several previously obtained remote/in-situ datasets (Mogul et al. 2021, Mahieux et al. 2024, Mahieux et al. 2023, Lincowski et al. 2021). As a result, several sulfur-based species previously not conclusively observed have now been definitively detected within remote sensing data (Mahieux et al. 2023), while debate rages on about species detected via in situ observation opportunities (Lincowski et al. 2021, Mogul et al. 2021).

Several gases recently positively detected by SOIR have absorption at UV wavelengths coincident with previously obtained Hubble Space Telescope spectra (Jessup et al. 2015, Jessup et al. 2020). We present a summary of the detectability of these species in the previously obtained Hubble data. We discuss what these and the recent SOIR retrievals may mean for anticipated monitoring of the Venus cloud top and middle atmosphere at UV and other wavelengths via the EnVision/VenSpec instrument (Marcq et al. 2021). We also discuss to what extent the detectability of these species at UV wavelengths impacts open controversial in-situ detections (Mogul et al. 2021); especially those that may directly impact the sulfur cycle or other cloud level atmospheric constituents (Rimmer et al. 2021).

REFERENCES:

Widemann, T., Smrekar, S.E., Garvin, J.B. et al. Venus Evolution Through Time: Key Science Questions, Selected Mission Concepts and Future Investigations. Space Sci Rev 219, 56 (2023). https://doi.org/10.1007/s11214-023-00992-w

Marcq, E., Mills, F. P., Parkinson, C., Vandaele, A.C. Composition and Chemistry of the Neutral Atmosphere of Venus space Sci Rev (2018) 214:10 DOI 10.1007/s11214-017-0438-5.

Bierson, C. J., & Zhang, X. (2020). Chemical cycling in the venusian atmosphere: A full photochemical model from the surface to 110 km. Journal of Geophysical Research: Planets, 125, e2019JE006159. https://doi.org/10.1029/2019JE006159

Rimmer, P. B. , Jordan, S.,  Constantinou, T., Woitke,  Shorttle, O. , Hobbs, R., and Paschodimas, A., Hydroxide Salts in the Clouds of Venus: Their Effect on the Sulfur Cycle and Cloud Droplet pH. Planetary Science Journal, 2:133 (25pp), 2021 https://doi.org/10.3847/PSJ/ac0156

Dai, L., Zhang, X., Shao, W. D., Bierson, C. J., & Cui, J. (2022). A simple condensation model for the H2SO4-H2O gas-cloud system on Venus. Journal of Geophysical Research: Planets, 127, e2021JE007060. https://doi.org/10.1029/2021JE007060

Dai, L., Shao, W. , and Sheng, Z., An investigation into Venusian atmospheric chemistry based on an open-access photochemistry-transport model at 0–112 km. Astronomy &Astrophysics, 689, A55 (2024) https://doi.org/10.1051/0004-6361/202450552

Jiang, C., Rimmer, Paul B. Rimmer,  et al. Iron-sulfur chemistry can explain the ultraviolet
absorber in the clouds of Venus., Sci. Adv. 10, eadg8826 (2024)

Mogul, R.   Limaye S.L.,  Way, M. J.,  Cordova, J. A., (2021)Venus' Mass Spectra Show Signs of Disequilibria in the Middle Clouds Geophys. Res. Letters. 48, Issue7, 2021e2020GL091327, https://doi.org/10.1029/2020GL091327

Jessup, K.-L., Marcq, E., Bertaux, J.-L., Mills, F.~P., Limaye, S., Roman, A.2020.\On Venus' cloud top chemistry, convective activity and topography: A perspective from HST. Icarus 335. doi:10.1016/j.icarus.2019.07.006

Stolzenbach, A.,  Lefèvre, F., Lebonnois, S.,  Määttänen, A., Three-dimensional modeling of Venus photochemistry and clouds, Icarus, Volume 395, 2023,115447, https://doi.org/10.1016/j.icarus.2023.115447.

Heays, A. N., Stark, G., Lyons, J. R., de Oliveira, N., Lewis, B. R., & Gibson, S. T. (2022). https://doi.org/10.1080/00268976.2022.2153092

Heays,A., Bosman, A.D. and E.F. Dishoeck Photodissociation and photoionization of atoms and molecules of astrophysical interest, Astronomy &Astrophysics 602,A105(2017) DOI:10.1051/0004-6361/201628742

Skog, R., Frandsen, B., Kurten, T., 2024. Simulating UV-VIS Spectra for Polysulfur Species in the Venusian Atmosphere.E GU General Assembly Conference Abstracts. doi:10.5194/egusphere-egu24-8798

Frandsen, B. and Skog, R.: Breaking New Ground in Venusian Atmospheric Sulfur Chemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7533, https://doi.org/10.5194/egusphere-egu24-7533, 2024.

Emmanuel Marcq, Franck Montmessin, Jérémie Lasue, Bruno Bézard, Kandis Lea Jessup, et al. Instrumental requirements for the study of Venus' cloud top using the UV imaging spectrometer VeSUV. Advances in Space Research, 2021, 68 (1), pp.275-291. 10.1016/j.asr.2021.03.012. insu-03179739

Jessup, K. L. Emmanuel Marcq, Franklin Mills. Arnaud Mahieux, et al. Coordinated Hubble Space Telescope and Venus Express Observations of Venus’ upper cloud deck Icarus 258 (2015) 309–336 http://dx.doi.org/10.1016/j.icarus.2015.05.027

Andrew P. Lincowski, Victoria S. Meadows, David Crisp, et al., 2021 ApJL 908 L44DOI 10.3847/2041-8213/abde47

Mahieux, S. Viscardy, K.L. Jessup, F.P. Mills, et al.  H2CO, O3, NH3, HCN, N2O, NO2, NO, and HO2 upper limits of detection in the Venus lower-mesosphere using SOIR on board Venus Express.  https://doi.org/10.1016/j.icarus.2023.115862

How to cite: Jessup, K. L., Mahieux, A., Marcq, E., Bhushan, A., and Mills, F.: Prospective Venus Cloud trace species detectability as inferred from Hubble, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1266, https://doi.org/10.5194/epsc-dps2025-1266, 2025.

Based on the state-of-the-art Venus Planetary Climate Model (PCM, formerly known as the Venus IPSL GCM) developed by our team[1-3], we have generated a Venus Climate Database (VCD) (http://www-venus.lmd.jussieu.fr/). This tool was developed with funding from ESA in the context of the preparation of the upcoming EnVision mission. The latest version of the VCD, VCD2.3, was released in fall 2023.

The VCD provides mean values and statistics of the main meteorological variables (atmospheric temperature, density, pressure and winds) as well as atmospheric composition and related physical fields. It extends from the surface up to and including the thermosphere (~250km). The database contains high resolution temporal outputs (using 24 hourly bins) enabling a good representation of the diurnal evolution of quantities over a climatological Venusian day.

As the goal of the VCD is to provide information about the state of the Venusian atmosphere, various realistic settings have been used to run a series of baseline GCM simulations, namely:

- Simulations using various Extreme UltraViolet (EUV) input from the Sun, as this forcing influences significantly the thermosphere (~120km and above).

- Some supplementary simulations with extreme values of UV cloud albedo, to bracket the state of the atmosphere below the thermosphere.

In addition to the aforementioned VCD scenarios, the following features are available:

- A "high resolution" mode based on a high resolution topography map (at 23 pixels/degree).

- Access to the Venusian intra-hour variability (RMS) of main meteorological variables, as well as the Venusian day-to-day variability thereof.

- The possibility to add perturbations to the climatological fields in order to generate realistic weather conditions.

VCD2.3 is distributed as (i) a main Fortran subroutine that users can interface and directly call from their own programs, interfaces to call this gateway routine using other programming languages (e.g. C, Python, IDL, Matlab, ...) are also provided; (ii) a web interface, for quick looks (http://www-venus.lmd.jussieu.fr).

We are currently working on the next version of the VCD, which should include not only updated Venus PCM simulation outputs (improved gravity waves scheme and better tuning of atmospheric oxygen) , but also some improvements in the VCD software (a redesigned gravity waves variability scheme, in line with the PCM updates) as well as on the inclusion of Global Climate Model simulation outputs from other teams.

References:

[1] Martinez, A .et al. Exploring the variability of the venusian thermosphere with the IPSL Venus GCM, Icarus (2023), DOI: 10.1016/j.icarus.2022.115272

[2] Stolzenbach, A. et al. Three-dimensional modeling of Venus photochemistry and clouds, Icarus, (2023), DOI: 10.1016/j.icarus.2023.115447

[3] Martinez, A. et al. Three-dimensional Venusian ionosphere model, Icarus (2024), DOI: 10.1016/j.icarus.2024.116035

How to cite: Millour, E., Lebonnois, S., Kovalenko, I., Martinez, A., Forget, F., Spiga, A., Cipriani, F., and development team, T. V.: The Venus Climate Database, current and future versions, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1256, https://doi.org/10.5194/epsc-dps2025-1256, 2025.

The 2030s will see the arrival of several spacecrafts, with multiple spectrometers designed to measure the atmosphere or surface using the transparency windows through the clouds on the nightside. In this work we summarize the data analysis of the VIRTIS-M dataset most relevant to the upcoming missions. We compare these results to simulations using these latest available inputs to investigate discrepancies and discuss the needs for improvements in preparation for the future missions.

The VIRTIS (Visible and Infra-Red Thermal Imaging Spectrometer) instrument was the imaging spectrometer on-board Venus Express. The mapping channel (VIRTIS-M) covering the 0.25 - 5.1µm range (Cardesín-Moinelo et al., 2020) and observed the surface and lower atmosphere on the Venus nightside. Several instruments as part of the upcoming Venus missions will study within this range. In particular, Venus Emissivity Mapper and VenSpec-M are mappers that will investigate between 0.86 and 1.18 µm (Hagelschuer et al., 2024) and VenSpec-H is a high-resolution spectrometer that will investigate between 1.1 and 2.5 µm (Robert et al., 2025). We study the expected radiance at the top of atmosphere (TOA) on nightside, since this effect the instrument performance (e.g. SNR) and geographic/measurement coverage.

Previous works have thoroughly analyzed the transparency windows (Cardesín-Moinelo et al. 2020; Mueller et al., 2020). We summarize the previous work between 1 and 2.5 µm and reanalyze in the view of upcoming missions to make consistent database for the TOA radiances.

Figure 1 Average and standard deviation of Venus TOA radiance from VIRTIS-M in 3 transparency windows (left 1.18 µm, center 1.74 µm, right 2.4 µm). The averages are separated into 4 latitude bins in the southern hemisphere: 0 to -30°: low-latitude; -30° to -60°: mid-latitude; -60° to -75°: cold collar; and -75° to -90°: polar vortex. Some filtering and corrections as suggested in the literature were applied.

The nightside TOA radiances have been previously modelled and used for the retrieval of atmospheric and surface parameters. The transparency window TOA radiances are highly impacted by the aerosols scattering and CO₂ absorption. Parameterizations of these effects are used in separate spectral ranges to efficiently approximate their true features. We implement these together in a radiative transfer model to present our best effort at a global model of the nightside TOA radiances expected for the future mission.

We use the ASIMUT-ALVL radiative transfer model to simulate the TOA radiances. The Venus Climate Database (Lebonnois et al., 2010) is used for atmospheric temperature, pressure, and molecular Volume Mixing Ratio (VMR). The commonly used results from Haus et al. (2016) are used for the vertical profiles of the 4 aerosols sizes. HITRAN 2020 (Gordon et al., 2022) and the Voigt line profile with CO₂ pressure broadening (when available) is used for all molecules except CO₂. For CO₂, the sub-Lorentzian profile of Bézard et al. (2011) is used along with the continuum values from several works (Bézard et al., 2009; Bézard et al., 2011; Haus et al., 2010; Kappel et al., 2012).

The TOA radiances are presented in comparison with the data analysis from above. There are notable differences across the wavelength regions. We aim to correlate these to specific physical features to propose as useful targets for future updates.

References

Bézard, B., Tsang, C., Carlson, R., Piccioni, G., Marcq, E., and Drossart, P., “Water vapor abundance near the surface of Venus from Venus Express/VIRTIS observations,” Journal of Geophysical Research: Planets 114 (2009).

Bézard, B., Fedorova, A., Bertaux, J.-L., Rodin, A., and Korablev, O., “The 1.10- and 1.18-m nightside windows of Venus observed by SPICAV-IR aboard Venus Express,” Icarus 216 (2011).

Cardesín-Moinelo, G. Piccioni, A. Migliorini, D. Grassi, V. Cottini, D. Titov, R. Politi, F. Nuccilli, P. Drossart, “Global maps of Venus nightside mean infrared thermal emissions obtained by VIRTIS on Venus Express,” Icarus 343 (2020).

Gordon, I., Rothman, L., Hargreaves, R., Hashemi, R., Karlovets, E., Skinner, F., et al., "The HITRAN2020 molecular spectroscopic database", J. Quant. Spectrosc. Radiat. Transfer 277, (2022).

Hagelschuer, T., Pertenais, M., Walter, I., Dern, P., del Togno, S., Säuberlich, T., Pohl, A., Rosas Ortiz, Y.M., Westerdorff, K., Kopp, E., Fitzner, A., Arcos Carrasco, C., Wendler, D., Ulmer, B., Ziemke, C., Rufini Mastropasqua, S., Lötzke, H.-G., Alemanno, G., Carron, J., Réess, J.M., Vandaele, A.C., Robert, S., Marcq, E., Helbert, J., Peter, G., “The Venus Emissivity Mapper (VEM): instrument design and development for VERITAS and EnVision,” Infrared Remote Sensing and Instrumentation XXXII, Proceedings of the optical engineering + applications conference (2024).

Haus, R. and Arnold, G., “Radiative transfer in the atmosphere of Venus and applications to surface emissivity retrieval from VIRTIS/VEX measurements,” Planetary and Space Science 58 (2010).

Haus, R., Kappel, D., Tellmann, S., Arnold, G., Piccioni, G., Drossart, P., Häusler, B., “Radiative energy balance of Venus based on improved models of the middle and lower atmosphere,” Icarus 272 (2016).

Kappel, D., Arnold, G., Haus, R., Piccioni, G., and Drossart, P., “Refinements in the data analysis of VIRTIS-M-IR Venus nightside spectra,” Advances in Space Research 50 (2012).

Lebonnois, S., Hourdin, F., Eymet, V., Crespin, A., Fournier, R., Forget, F., “Superrotation of Venus' atmosphere analyzed with a full general circulation model,” Journal of Geophysical Research (Planets) 115 (2010).

Mueller, N., Smrekar, S., Tsang, C., “Multispectral surface emissivity from VIRTIS on Venus Express,” Icarus 335 (2020).

Robert, S., Erwin, J., De Cock, R., Thomas, I.R., Pereira, N., Jacobs, L., Berkenbosch, S., Bolsée, D., Vanhellemont, F., Neefs, E., Aoki, S., Bézard, B., Marcq, E., Alemanno, G., Helbert, J., Vandaele, A.C., “Scientific objectives and instrumental requirements of the infrared spectrometer VenSpec-H onboard EnVision”. Journal of Applied Remote Sensing 19.1 (2025).

How to cite: Erwin, J., Robert, S., Ducreux, E., Garate Lopez, I., Reyes Guerrero, J., Cardesin, A., and Mueller, N.: Venus nightside radiances data analysis and model comparison in view of upcoming Venus missions, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1428, https://doi.org/10.5194/epsc-dps2025-1428, 2025.

1. Introduction

The cloud layer of Venus between 47 and 70 km is home to a vivid sulfur chemistry and microphysics, with SO₂ as the major gas species and condensed phase composed of H₂SO₄ and H₂O. This cloud layer has been extensively observed and modelled. The main discrepancy between the observation and models in the SO₂ vertical gradient throughout the cloud, no chemical model is able to reproduce the 3 order of magnitude decrease between the base and top of the cloud layer. Polysulfur chemistry could a candidate for buffering significant sulfur atoms, as it can grow into long chain and possibly condense. Strong absorption in Spectrophotometer data from VENERA 11, 12, 13 and 14 at 450–600 nm between 10 and 30 km recorded strong absorptions attributed most commonly to gaseous elemental sulfur S_x (Maiorov et al., 2005), and correlating S₃ spectral features from Venera-11 with an increase with altitude from 0.03 ppbv at 3 km to 0.1 ppbv at 19 km (Maiorov et al., 2005). The presence of S3 and other sulfur allotropes polysulfur (S_x) in the clouds has been hypothesized from Vega probes (Porshnev et al., 1987), but no definitive detection of S_x in this region has been performed. S_x is a potential candidate to the UV unknown absorbed (Toon et al., 1982; Pérez-Hoyos et al., 2018). H₂S were measured at ppm values below the clouds by the Pioneer Venus mission. (Hoffman et al., 1980; Oyama et al., 1980). DAVINCI will measure sulfur allotropes and H₂S in the deep atmosphere (Garvin et al., 2022). For the first time in 3D and with realistic photolysis, we studied the impact of these species into the Venus cloud chemistry.

2. Model
The 3D Venus Planetary Climate Model (PCM) is used (Garate-Lopez and Lebonnois, 2018). The photochemical model describes the comprehensive chemistries of CO₂, CO, hydrogen, oxygen, chlorine, sulfur and nitrogen down to roughly 35 km (Stolzenbach et al., 2023; Streel et al., 2025). In this study we added five species H₂S, HS, S₃, S₄, S₈ and 34 reactions to the gas phase chemistry. The PCM takes into account the condensation of H₂SO₄ and H₂O based on the hypothesis that clouds are at all times in a state of thermodynamic equilibrium, i.e. following exactly the saturation pressure profile of the calculated equilibrium H₂SO4 aqueous solution. The same philosophy is used for the polysufur condensation/evaporation in the model. We allow S₂, S₃, S₄ and S₈ to condense following (Zahnle et al., 2016). Photolysis rates are calculated online, following the same formalism as in the Mars version of the PCM (Lefèvre et al., 2021). The
screening effect of all ultraviolet-absorbing species in the computation of the photolysis rates is taken into account. The radiative transfer computation is performed over the range of 0-815 nm. Four photodissociations were added following recent theoretical calculations, and the spectra of S₂ was updated.

3. Results
Fig 1 shows the zonal-mean distribution of condensed S₂, reaching 0.25 ppm at the cloud-top. It is the dominating species of the sulfur allotrope due to its low saturation mixing ratio. In total this chemistry can store up 0.5 ppm with a low SO₂ value below the clouds, and around 4 ppm with realistic SO₂ values. Polysulfur cloud chemistry appears to be a substantial sulfur buffers but not large enough to explain the SO₂ cloud vertical gradient. H₂S is stable with few tenths of ppm in the lower clouds.

Fig 1: Zonal-mean distribution of condensed S₂ in ppmv

References
Garate-Lopez, I., & Lebonnois, S. (2018). Icarus, 314:1–11.
Garvin, J. B., Getty, S. A., Arney, G. N., et al. (2022). The Planetary Science Journal, 3(5):117.
Hoffman, J. H., Hodges, R. R., Donahue, T. M., et al. (1980). Journal of Geophysical Research, 85:7882–7890.
Lefèvre, F., Trokhimovskiy, A., Fedorova, A., et al. (2021). Journal of Geophysical Research (Planets), 126(4):e06838.
Maiorov, B. S., Ignat’ev, N. I., Moroz, V. I., et al. (2005). Solar System Research, 39(4):267–282.
Oyama, V. I., Carle, G. C., Woeller, F., et al. (1980). Journal of Geophysical Research, 85:7891–7902.
Pérez-Hoyos, S., Sánchez-Lavega, A., García-Muñoz, A., et al. (2018). Journal of Geophysical Research (Planets), 123:145–162.
Porshnev, N. V., Mukhin, L. M., Gel’Man, B. G., et al. (1987). Kosmicheskie Issledovaniia, 25:715–720.
Stolzenbach, A., Lefèvre, F., Lebonnois, S., et al. (2023). Icarus, 395:115447.
Streel, N., Lefèvre, F., Martinez, A., et al. (2025). Submitted to JGR: Planets.
Toon, O. B., Turco, R. P., & Pollack, J. B. (1982). Icarus, 51:358–373.
Zahnle, K., Marley, M. S., Morley, C. V., et al. (2016). The Astrophysical Journal, 824:137.

How to cite: Lefevre, M., Lefevre, F., Määttänen, A., Frandsen, B., Skog, R., Stolzenbach, A., and Braude, A.: Sulfur allotropes and sulfur hydrides on the Venus cloud chemistry, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-306, https://doi.org/10.5194/epsc-dps2025-306, 2025.

Venus, has been studied by numerous space missions over decades, yet its past water inventory remains poorly constrained, obscuring insights into planetary evolution and the emergence of habitability. A critical factor in understanding its history is the atmospheric deuterium-to-hydrogen (D/H) ratio, which offers insights into Venus' water loss and atmospheric escape mechanisms. Previous measurements of this ratio have been confined to altitudes near or below the exobase of about 250 km, based on remote sensing and in situ water vapor observations. In this study, we reanalyze magnetic field data from Venus Express to examine pick-up generated ion cyclotron waves (PCWs) caused by hydrogen ions. For the first time, we also apply the same method to study PCWs generated by the pick-up of deuterium ions, presenting the first altitude-dependent density profile of deuterium in Venus' extended exosphere. Our results also align with recent studies and indicate that the escape rates of deuterium and hydrogen fractionate insufficient to support the existence of a late-stage ocean on Venus, reinforcing the notion that Venus may have never been habitable due to its inability to retain significant water over time.

How to cite: Weichbold, F., Lammer, H., Scherf, M., Schmid, D., Simon-Wedlund, C., Mazelle, C., Constantinou, T., Volwerk, M., Woitke, P., Eminger, P., and Ferus, M.: Constraining Venus’ Water Loss History through D/H Ratio Observations from Ion Cyclotron Wave Analysis in the extended Exosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1437, https://doi.org/10.5194/epsc-dps2025-1437, 2025.

Venus has a thick atmosphere with many of its chemical and photochemical processes yet to be fully understood. While it mainly consists of relatively inert CO₂ and N₂, the trace gases, which include chlorine and sulfur compounds, are responsible for Venus's rich and diverse chemistry and photochemistry. Given that chlorine has two stable isotopes and sulfur has four, there are plenty of opportunities for naturally occurring isotopic effects in Venusian atmospheric chemistry. Oxygen, carbon, and hydrogen also typically participate in Venusian chlorine and sulfur chemistry, providing further diversity in isotopes to study.

Using high-level computational chemistry methods in synergy with experimental kinetics, we model temperature-dependent rate coefficients. Furthermore, the computational chemistry approaches are used to model mass-dependent rate coefficients to study how isotopic fingerprints in the reactants and products from the chemistry may arise. I will present our recent work involving CO oxidation in the Venusian atmosphere and how the measurement of isotopic signals can inform us which chemical mechanism dominates CO oxidation on Venus. The discrepancy between models and observations of O₂ abundance in the Venusian mesosphere remains an issue. The Cl radical oxidation of CO may explain the missing O₂ in the Venusian mesosphere, as the cycle consumes O₂ efficiently: Cl + CO ↔ ClCO + O₂ → ClC(O)OO → ClO + CO₂. The initial equilibrium between Cl and CO is identified as the bottleneck for propagating the radical oxidation cycle.

We show how the isotopic fingerprint in CO from the Cl radical oxidation cycle is ripe for detection on Venus through microwave spectroscopy and how important getting the isotopic ratio correct is for retrievals of other properties. Alternative CO oxidation mechanisms are also explored, and other isotopic fingerprints may be investigated, for example, for the ClO radical, which has been observed in the Venusian atmosphere. Our work provides quantitative numbers for isotopic fractionation, which are needed to interpret which chemical processes dominate on Venus. Fractionation of naturally occurring isotopes on Venus provides detectable signatures for future missions through either spectroscopy (IR or microwave) or mass spectrometry. Notably, NASA’s DAVINCI mission will include a mass spectrometer in its payload.

Our work is a collaboration between theory and experiments, providing a detailed mechanistic and quantitative understanding of CO chemistry in the Venusian mesosphere. It is additionally relevant to understanding the isotopic fractionation of the atmosphere of Archean Earth (pre-oxygen era) and Noachian Mars, where large mass-independent signatures of CO related compounds can be found, e.g., in Martian soil carbon.

How to cite: Frandsen, B., Skog, R., Chao, W., Jones, G., Pham, K., Mills, F., Okumura, M., Andersen, M., Percival, C., and Winiberg, F.: CO Oxidation in the Venusian Mesosphere and Associated Isotopic Fingerprints Enabling Detection and Chemical Mechanism Insights, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-603, https://doi.org/10.5194/epsc-dps2025-603, 2025.

Introduction

In this work, we describe new and transformative insights into the composition of Venus’ aerosols using uncharacterized data acquired by the Pioneer Venus Large Probe (PVLP), which descended through Venus’ atmosphere in 1978 [1]. During the descent, the PVLP inadvertently collected cloud aerosols and measured the decomposition of their contents [2]. In the initial post-flight PVLP investigations, aerosol collection and analysis were inferred for the Large Probe Neutral Mass Spectrometer (LNMS) [2] and considered for the Large Probe Gas Chromatograph (LGC) [3].

Here, we demonstrate that the LNMS data contain several uncharacterized mass signals, which directly relate to the thermal decomposition of aerosols possessing a heterogeneous chemical composition. Accordingly, we re-analyzed and re-interpreted the altitude trends from the LNMS data and LGC results as the evolved gas analyses that followed the temperature gradient of the PVLP descent (-30 to 462 ˚C, ~ 65 to 0 km [4]).

Methods

Thermal decomposition profiles from the LNMS data were constructed by plotting the number densities for SO₂, H₂O, SO₃, and O₂ against the LNMS inlet temperatures, which were heated during operation. The LNMS inlet temperatures were obtained using data from the LNMS project reports [5] and PVLP descent timeline [6]. The mass spectra obtained at the electron ionization energies of 70, 30, and 22 eV were independently treated using the procedures described in [7-9]. The peaks for SO₂, H₂O, SO₃, and O₂ in the thermal profiles were fit to Gauss functions and the regressions minimized by least squares analysis. Using the stoichiometry in Reactions 1-3, the peak areas for SO₂ and H₂O were converted to weight percent (w%) and mass loading (mg m^-3) for H₂SO₄, Fe₂(SO₄)₃, and H₂O (after correction for the H₂O from Reaction 1). Review of the LNMS CO₂ density profile [9] revealed that aerosols were collected between ~ 51.0 to 48.4 km. The collection column was treated as a cylinder with a height of 2.6 km and diameter of 0.98 m, which equaled the outer PVLP diameter [10].

H₂SO₄  →  SO₃  +  H₂O                   (1)

SO₃  →  SO₂  +  0.5 O₂                    (2)

Fe₂(SO₄)₃  →  Fe₂O₃ +  3 SO₃       (3)

Results and Discussion

The LNMS mixing ratios (x) for SO₂ and H₂O (Fig. 1) are inconsistent with other Venus measurements obtained spectroscopically. Yet, after aerosol capture (< 51.0 km, Fig. 1), the LNMS and LGC xSO₂ and xH₂O are within error (or comparable). Moreover, the cloud xH₂O from the LNMS are lower than other Venus measurements obtained by direct analyses (Fig. 1). These combined results suggest that the xSO₂ and xH₂O from the LNMS and LGC do not represent atmospheric gases. Instead, the LNMS and LGC xSO₂ and xH₂O the represent the gases released during the thermal decomposition of the captured aerosols. The differing maxima observed in the LNMS xSO₂ and xH₂O (at ~ 35 and 10 km) suggest the decomposition of ≥ 2 sulfate-bearing compounds from the captured aerosols.

Re-expression of the LNMS data as evolved gas profiles (Fig. 2) revealed the temperature-dependent release of SO₂, H₂O, SO₃, and O₂ from the captured aerosols. Parsing of the LNMS data additionally revealed signals consistent with the release of metal-bearing species (e.g., FeO⁺ and MgSO₄⁺). These results are consistent with an aerosol composition including H₂SO₄, hydrated ferric sulfates, possibly hydrated magnesium sulfate, and other hydrates. The thermal decomposition reactions for H₂SO₄ and ferric sulfates are provided in Reaction 1-3. The inferred aerosol relative abundances amounted to 22 ± 4 wt% H₂SO₄, 16 ± 3 wt% Fe₂(SO₄)₃ (projected), and 62 ± 8 wt% H₂O. The aerosols H₂O predominantly released from hydrates between ~ 270–460 ˚C (59 ± 8 wt%), consistent with the loss of H₂O from hydrated iron and magnesium sulfates and other hydrates (e.g., [11, 12]).

Thus, this work reveals that Venus’ aerosols contain a previously underestimated reservoir of water and possible altered materials derived from iron and magnesium of cosmic origin. These results provide new considerations for cloud chemistry models and cloud habitability discussions.

Figure 1. The LNMS apparent mixing ratios for (A) SO₂ and (B) H₂O compared to the LGC and other Venus measurements. Brackets to the right side of the plots indicate where the differing aerosol components decomposed. The LNMS values (squares) were obtained from the spectra obtained at 70 eV (red squares) and 30 and 22 eV (green squares). The LGC (yellow circles) error bars represent the reported 3 s confidence intervals. The comparative Venus values (green triangles) for (A) SO₂ and (B) H₂O are respectively labeled in the top legends. Pertinent abbreviations include NIR (near infrared spectroscopy), GC (gas chromatograph), UVS (UV spectroscopy), V12 (Venera 12), V13/14 (Venera 13 and 14), and V11/13/14 (Venera 11, 13, and 14).

Figure 2 The LNMS evolved gas profiles for (A) SO₂ and (B) H₂O expressed against the LNMS inlet temperatures (lower x-axis) and associated altitudes (upper x-axis). Number densities are from the 70 (circles), 30 (squares), and 22 eV (diamonds) spectra. Fits to the LNMS data (solid red lines) represent the sum of the numbered Gauss peaks (dashed lines). Temperatures at maximum decomposition (T_D) for each peak (n) are listed. Dotted lines demark the LNMS clog (~ 50-25 km).

References

[1] Fimmel R. O. Pioneer Venus (1983) Scientific and Technical Information Branch, NASA.

[2] Hoffman J. H. et al. (1980) JGR Space Sci., 85, 7882-7890.

[3] Oyama V. I. et al. (1979) Science, 205, 52-54.

[4] Seiff A. et al. (1985) Adv. Space Res., 5, 3-58.

[5] Final Report, Large Probe Neutral Mass Spectrometer, August 31, 1978, NASA Ames Research Center History Archives, Collection Number AFS8100.15A.

[6] Seiff A. et al. (1980) JGR Space Sci., 85, 7903-7933.

[7] Mogul R. et al. (2021) GRL, 48, e2020GL091327.

[8] Mogul R. et al. (2023) Icarus, 392, 115374.

[9] Mogul R. et al. (2023) MethodsX, 11, 102305.

[10] Dutta S. et al. In AIAA SCITECH 2023 Forum (2023), 1165.

[11] Lauer Jr H. et al. In 31st Lunar and Planetary Science (2000), 20000085925.

[12] Spratt H. et al. (2014) J. Therm. Analysis Calorim., 115, 101-109.

How to cite: Mogul, R., Zolotov, M., Way, M., and Limaye, S.: Iron sulfate, sulfuric acid, and water are major components in Venus’ aerosols , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1089, https://doi.org/10.5194/epsc-dps2025-1089, 2025.

Upcoming missions to Venus will be equipped with advanced spectrometers capable of resolving fine atmospheric spectral features. To fully exploit this observational potential, accurate spectroscopic parameters adapted to Venus’ CO₂-rich atmosphere are required. In particular, the retrieval of water vapor concentrations relies heavily on appropriate collisional parameters. However, current spectroscopic databases lack CO₂-broadening parameters for H₂O, and air-broadening parameters are often used as substitutes (Jorge et al., 2024), which can introduce significant biases in retrieved H₂O concentrations.

To address this issue and to follow up the work of Régalia et al. (2019), new high-resolution infrared spectra of H₂O broadened by CO₂ were recorded in spectral regions of planetary interest (1.18, 2.34, and 2.7 µm), using the Fourier Transform Spectrometer at the GSMA laboratory in Reims, France. For 187 isolated H₂O transitions, CO₂-broadened half-widths and pressure-shift coefficients were determined through a multi-spectrum fitting procedure using the Voigt profile (Plateaux et al., 2001; Lyulin, 2015). To take into account finer physical effects, a quadratic speed-dependent Voigt profile (Ngo et al., 2012, 2013) was also applied, allowing the measurement of speed-dependence coefficients for 106 transitions.

The Voigt experimental results were used to improve the molecular interaction potential of the H₂O–CO₂ collision system. Since experimental data alone are not sufficient to entirely model an atmospheric spectrum, new calculations were performed using the semi-classical Complex Robert-Bonamy-Ma (CRBM) formalism (Robert & Bonamy, 1979; Ma et al., 2007). This allowed the determination of half-widths and pressure shifts for thousands of H₂O transitions. Several key atmospheric windows of Venus were considered: 1.18, 1.38, 1.74, and 2.34 µm. The resulting calculated linelist can now be directly used in radiative transfer applications (Ducreux et al., 2024, 2025 submitted).

The impact of using these new CO₂-collisional parameters for water vapor retrievals was evaluated through simulations using the ASIMUT-ALVL radiative transfer code (Vandaele et al. 2006; Spurr, 2008). Venusian spectra were simulated in different infrared windows probing various altitude ranges on both the nightside and dayside of the planet. For each case, 1000 spectra were generated using the new CO₂-specific linelist, with added Gaussian noise based on a selected signal-to-noise ratio. Retrievals were then performed using the standard air-broadening linelist from HITRAN2020 (Gordon et al., 2022) for the entire statistical sample. The dependence on spectral resolution and signal-to-noise ratio were also investigated. The results demonstrate that relying on spectroscopic parameters not suited for a CO₂-rich atmosphere can lead to significant errors in retrieving water vapor concentrations on Venus. This highlights the inadequacy of air-broadening parameters for a CO₂-dominated environment and highlights the necessity of dedicated spectroscopic data for accurate retrievals.

Moreover, the need for accurate spectroscopic parameters to study CO₂-rich atmospheres also applies to the main deuterated isotopologue of water vapor, HDO. New spectra of HDO broadened by CO₂ were therefore recorded in the same spectral regions as H₂O and CO₂-collisional parameters for HDO have been derived to build a measured linelist, which will soon be augmented with CRBM calculations. The final objective is to provide the planetary community with a CO₂-specific linelist for HDO, suitable for radiative transfer modelling in CO₂-rich planetary atmospheres.

How to cite: Ducreux, É., Grouiez, B., Vispoel, B., Gamache, R. R., Lepère, M., Régalia, L., and Robert, S.: New CO2-collisional parameters for H2O: their impact on water vapor retrievals in Venus’ atmosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-753, https://doi.org/10.5194/epsc-dps2025-753, 2025.

Introduction

Venus is set to be a key part of the next decades of planetary exploration with several missions planned by NASA and ESA (DAVINCI, VERITAS, EnVision). These missions aim to better understand how Venus and the Earth started being so similar but evolved into such different worlds. Modelling the Venus atmosphere is essential to support past and future observations. The Venus Planetary Climate Model (Venus PCM) used in this study is a 3D model that has been developed by the Laboratoire de Météorologie Dynamique (LMD) for more than 15 years in collaboration with other institutions, including the Instituto de Astrofísica de Andalucía (IAA-CSIC) [1,2,3].

The Venus PCM has been used to simulate the Venus photochemistry and clouds from the surface to the bottom of the thermosphere [4], and here we use the last version of the model with the goal of shedding a light on the mesospheric SO₂ issue. Not only is this species highly variable in Venus mesosphere, but reproducing the observed SO₂ depletion in the cloud layer also remains challenging. In particular, the three orders of magnitude depletion is not well reproduced by models, which can only simulate a decrease from 10 ppmv at 40 km to 0.1 ppmv at 80 km [4].

The interest of studying SO₂ lies in its fundamental role in the cloud formation in Venus. In particular, SO₂ is the source to form the sulfuric acid H₂SO₄ that is part of the binary mixture (H₂SO₄-H₂O) that defines the droplets in the clouds of Venus.

Implementation of in-droplets sulphur chemistry

In this work, we aim to reproduce the observed variation of SO₂ with altitude by using in-droplet sulphur chemistry for the first time in the Venus PCM, following the work by [5], in which they consider that clouds contain hydroxide salts like NaOH, which drive the droplet chemistry. NaOH is a proxy used in that study to represent other plausible sources of delivered hydrogen. They presented the following set of chemical reactions, whose rates are tuned to emulate the dissolution of SO₂ into the cloud droplet, and its release into gas phase when the droplet rains out and evaporates

As a first step, we implemented this set of chemical reactions in the Venus PCM. Preliminary results show that we can dissolve SO₂into the clouds using the chemical reactions from [5] with SO₂ initialized to a value of 150 ppmv below 40 km, in line with available observations.

We will present on-going work aimed to implement the full set of reactions proposed by [5] and we will discuss the implication of model results in the interpretation of future Envision observations.

Keywords: Venus atmosphere, General Circulation Model, cloud, chemistry.

Acknowledgments: Severo Ochoa grant CEX2021-001131-S funded by MICIU/AEI/ 10.13039/501100011033; Program EMERGIA 2021 (EMC21 00249); Spanish MCIU, the AEI and EC-FEDER funds under project PID2021-126365NB-C21.

References:
[1] Lebonnois et al. 2010, JGR, Vol.115, Issue E6
[2] Gilli et al. 2021, Icarus, Vol. 366, 114432
[3] Martinez et al. 2024, Icarus, Vol. 415, 116035
[4] Stolzenbach et al. 2023, Icarus, Vol. 395, 115447
[5] Rimmer et al. 2021, Planet. Sci. J., Vol. 2, 133

How to cite: Mendi-Martos, A., Gilli, G., Stolzenbach, A., Martinez, A., and Lara, L.: Towards in-droplet sulphur chemistry in the Venus clouds with the Venus Planetary Climate Model, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1368, https://doi.org/10.5194/epsc-dps2025-1368, 2025.

The study of HDO and the deuterium/hydrogen (D/H) ratio plays a critical role in reconstructing the past and present climate of Venus. These isotopic tracers offer valuable insights into the planet’s hydrological history, atmospheric escape processes, and potential ancient reservoirs of water. In particular, variations in D/H can shed light on the mechanisms that led Venus to become the hot, arid world we observe today.

In this work, we present the first fully three-dimensional simulation of the HDO cycle on Venus, by implementing HDO in both gas and liquid phases within the Venus Planetary Climate Model (VPCM). Our model allows us to explore the spatial and temporal behavior of HDO, and how it interacts with the atmospheric dynamics and cloud chemistry of Venus.

One of our key findings is that the vertical distribution of D/H is strongly influenced by processes previously neglected in earlier models. Notably, we show that the presence of deuterated sulfuric acid (HDSO₄) in Venusian clouds can significantly alter the D/H profile and must be taken into account in future studies.

We also assess the individual effects of isotope fractionation during three key processes: condensation, molecular diffusion, and photolysis. Our analysis reveals that photolysis-induced fractionation dominates the D/H ratio in the upper atmosphere, driving its increase to approximately 480 × VSMOW (Vienna Standard Mean Ocean Water) at altitudes near 130 km.

In addition, we observe notable diurnal variations in the abundances of H₂O, HDO, and D/H in the upper atmosphere, consistent with expectations based on solar-driven atmospheric dynamics.

Overall, our results highlight the complex interplay of physical and chemical processes controlling the distribution of water isotopologues on Venus. These findings not only refine our understanding of the present Venusian atmosphere but also provide essential constraints for reconstructing its climatic evolution and water loss history.

How to cite: Li, D., Montmessin, F., Lefèvre, F., Petzold, G., Xu, Q., Streel, N., and Lebonnois, S.: Understanding the Importance of HDO and D/H on Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-629, https://doi.org/10.5194/epsc-dps2025-629, 2025.

Introduction

The Venusian surface is profoundly shaped by complex endogenic phenomena, among which coronae represent critical insights into mantle-lithosphere interactions distinct from Earth’s plate tectonics. These volcanic-tectonic structures, circular to elliptical in geometry and spanning from tens to over a thousand kilometers, serve as windows into Venus's internal dynamics. Contrasting Earth's tectonic activity, Venus exhibits alternative geodynamic modes, including stagnant lid [1], episodic lid [2], and plutonic squishy lid regimes [3], dictated by its unique thermal state and lithospheric properties. Such conditions have led to extensive resurfacing events, resulting in a planetary surface younger than one billion years [4].

Various numerical and conceptual models have been proposed for coronae formation. Early models emphasized diapir-driven processes creating dome-shaped topography, followed by gravitational relaxation into annular configurations [5], the retrograde subduction as a potential mechanism for larger coronae, exhibiting trench-outer rise morphology [6]. Recent modeling has revealed complex plume-lithosphere interactions, including lithospheric instabilities at plume margins [4], plume-induced subduction [7], and intricate processes such as episodic subduction and plume underplating [8]. Peel-back delamination [4], plume-induced melt accumulation dynamics [9], and fracture-rim relationships [10]. These diverse mechanisms suggest corona formation may involve multiple processes rather than a singular mechanism.

Here, we present results from three-dimensional scaled analog experiments designed to investigate the influence of lithospheric drips—downward-moving dense lithospheric segments—and mantle dynamics on corona evolution. Employing precisely scaled laboratory simulations, complemented by detailed structural analyses, we demonstrate the significant role lithospheric instabilities play in governing deformation patterns and morphological characteristics of coronae. Our approach effectively reconciles modeled strain distributions with observed corona structures, highlighting the fundamental importance of mantle downwellings as drivers of tectonic complexity on Venus, thus expanding our understanding beyond conventional tectonic paradigms.

Results & Conclusion

The Venusian surface presents intricate tectonic patterns that have persistently challenged conventional geodynamic interpretations. Historically, mantle plume processes have dominated explanations of corona formation, potentially overshadowing the significant role lithospheric drips may play. In this work, we argue for a refined geodynamic model that explicitly incorporates lithospheric instabilities alongside mantle plumes to explain observed corona structures more comprehensively. Experimental outcomes clearly demonstrate spatial associations between areas of crustal thickening and shortening at corona troughs and corresponding subsurface downwelling zones, coupled simultaneously with tensile regimes inducing localized crustal stretching. These laboratory-derived models yield temporal deformation predictions that strongly align with structural observations at Atahensik Corona [11].

Terrestrial analogs underscore the critical role lithospheric instabilities—specifically drip processes—have in crustal deformation, producing characteristic central compression zones surrounded by peripheral extensional regions [12]. Our quantitative analysis of asymmetric corona topography reveals systematic correlations between corona rim elevation and central depression depth. Further structural analysis, examining cross-cutting fault relationships, elucidates a clear sequence of deformation marked by oblique faulting to radial and concentric patterns as the geodynamic regime evolves. During the evolution of the model, our results sequentially predict crustal thickening driven by surface stresses, initiating with subsidence, progressing through concentric trough, and this dynamic regime is consistent with observed fault developments. These structural criteria offer measurable parameters capable of distinguishing between coronae driven predominantly by mantle plume processes and those significantly influenced by lithospheric dripping. The coexistence of extensional and compressional tectonic features, such as rift zones adjacent to fold-and-thrust belts, emphasizes the value of integrating lithospheric drip processes into broader planetary tectonic frameworks.

References

[1] Solomatov & Moresi, (1996) [2] Turcotte, D. L. (1993) [3] Lourenço, D. L., et al. (2020) [4] Adams, G.F., et al. (2022) [5] Janes, D.M., et al. (1992) [6] Sandwell, D.T. and Schubert, G. (1992) [7] Davaille, A., et al. (2017) [8] Piskorz, D., et al. (2014) [9] Gülcher, A.J.P., et al. (2020) [10] Schools, J.W. and Smrekar, S.E. (2024) [8] Sabbeth, L., et al. (2024) [11] Kenkmann, T., et al. (2024) [12] Andersen, J., et al., (2024).

How to cite: Karagoz, O., Göğüş, O. H., Kenkmann, T., Bodur, Ö., Çetiner, A. B., and Göğüş, Ö. D.: Lithospheric Dripping explains Corona Formation on Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-576, https://doi.org/10.5194/epsc-dps2025-576, 2025.

The Venus Emissivity, Radio Science, InSAR, Topography, And Spectroscopy (VERITAS) mission, a Discovery class mission selected by NASA in 2021, is designed to answer fundamental questions about Venus’s geological activity and evolution, internal structure, and potential evidence of past or present interior water. VERITAS will carry two instruments – an X-band interferometric SAR (VISAR) and a near-infrared imaging spectrometer (VEM) – as well as a gravity science experiment to address these scientific objectives.

The VERITAS gravity science experiment will produce a global gravity map of significantly higher and more uniform spatial resolution than that achieved by the Magellan mission. Numerical simulations predict that VERITAS will achieve a gravity field spatial resolution between 85 and 120 km, with 90% of the planet mapped at a resolution better than 106 km. Additionally, VERITAS will retrieve important parameters related to Venus’s tidal response and rotational state, providing key constraints on its interior structure.

The gravity science investigation will rely on radio tracking data composed of range and Doppler measurement, collected via two coherent and simultaneous radio links in X and Ka bands. Thanks to the state-of-the-art quality of Doppler tracking data, the system is expected to deliver Doppler accuracy of approximately 18 μm/s  at 10 second integration time, for Sun-Probe-Earth (SPE) angles above 15°.

Previous simulations were performed under the reasonable assumption of white noise (uncorrelated measurements) in the tracking data. In this work, we present a more realistic analysis incorporating colored noise components (i.e. correlated measurement, with frequency dependent characteristics) into the Doppler error model. We quantify their impact on gravity field recovery and evaluate the validity of the white noise assumption.

Our analysis was carried out using JPL’s MONTE Orbit Determination software. The enhanced noise model includes contributions from both signal propagation effects and instrumentation noise from ground and onboard systems. Noise sources may be stationary or time-varying (e.g. seasonal variations in the troposphere, SPE dependence in plasma), and exhibit either white or colored spectral profiles (e.g.  plasma, frequency and timing systems). Colored components were generated using the algorithm described by [1] and incorporated into the filtering process via a whitening procedure applied prior to estimation, which normalizes residuals, flattens the power spectral density and decorrelates the measurement, since filtering processes in orbit determination typically assume uncorrelated measurements.

We present comparative results for the white-noise and colored-noise scenarios, focusing on gravity field recovery up to degree 220 in spherical harmonics.

The methodology developed for this study is not limited to VERITAS and can be applied to other radio science experiments.

[1] Timmer, J. and Koenig, M. (1995). On generating power law noise. Astronomy and Astrophysics, 300:707.

How to cite: Giuliani, F., De Marchi, F., Durante, D., Cascioli, G., Iess, L., Mazarico, E., and Smrekar, S.: Modeling Colored Noise in Doppler Tracking Data: Mapping Venus’s Gravity Field with VERITAS, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-739, https://doi.org/10.5194/epsc-dps2025-739, 2025.

The physical processes involved in the transition of a planet from a liquid magma ocean (‘MO’) to a convective solid mantle are still debated. Highly turbulent penetrative convection prevails when the MO is still liquid on the surface. But as the MO cools down in interaction with its atmosphere its upper surface thermal boundary layer (‘TBL’) will eventually first becomes partially molten, then solid. As soon as the rheological front, with a melt content less than 40%, reaches the surface, the upper part of the TBL could behave like a solid skin. This has led to suggest that MO cooling would always end up in a stagnant lid regime of convection, whereby mantle convection proceeds under a surface plate that remains stagnant, limiting the heat and volatile transfers to the atmosphere. This would help retaining water within the mantle, but would render the onset of subduction and plate tectonics more difficult (how to break a thick lid?). On the other hand, another family of cooling MO models suggests that the numerous impacts during the early stages of a planet would break repeatedly any floating skin on the MO, so that it would be difficult to establish a stagnant lid regime.

Laboratory experiments of penetrative convection-evaporation using visco-elasto-plastic colloidal dispersions (Di Giuseppe et al, 2012) suggest that two other phenomena could also be at play to destabilize the first solid skin: (1) melt flowing through a porous skin would generate in-plane compression that could generate buckling, exceed the yield strength of the material and initiate subduction; (2) rapid thermal contraction due to large temperature gradients across the skin could generate stresses large enough to exceed the yield strength and initiate subduction. We use these insights to explore the growth and stability of the TBL at the surface of a cooling magma ocean which interacts with a H₂O-CO₂ atmosphere. Our results indicate that, while on Earth, thermal stresses due to cooling could easily exceed the early lithosphere yield strength, this might not have been the case on Venus. On Venus, this process is strongly influenced by atmospheric conditions. For a high albedo of 0.5, the upper TBL could yield as early as 1.5 million years after cooling begins, similar to Earth, and therefore the MO stage would end up directly into a convective regime with repeated breaking and foundering of the lithosphere (e.g. subduction). But for an albedo of 0.3, thermal stresses never overcome the TBL’s yield strength. In such a scenario, the MO stage would end in a stagnant lid regime, which could act as a barrier to heat transfer and potentially filter degassing.

How to cite: Massol, H. and Davaille, A.: On the stability of the first solid skin at the surface of a magma ocean: stable on early Venus, breaking on early Earth ?, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1571, https://doi.org/10.5194/epsc-dps2025-1571, 2025.

Summary

The interior properties of Venus are still poorly constrained. We tested a new method to constrain its mantle viscosity. To do so we have used a unique feature of Venus’ surface: Baltis Vallis, a lava channel about as long as the Nile River on Earth. Since its formation, the terrain along Baltis Vallis has been deformed by the planet’s tectonics. We used mantle dynamics simulations from the StagYY code to model topography (elevation) and the rate at which it possibly changed (decorrelation time) during Venus’ recent history. Comparison with the properties of Baltis Vallis lead us to favor simulations using lower mantle viscosities (10²⁰ Pa s).

Figure 1: Location and topography of Baltis Vallis on Venus. Left panel: a global mosaic overlain with colorized topography showing Baltis Vallis's location. Right panel: a topographic map of Baltis Vallis in Atla Regio.

Background and motivation

Baltis Vallis (BV) is a 6,800-km long lava channel on Venus. Its apparent uphill flow direction must be a consequence of deformation changing topography after flow emplacement. The topography of BV thus retains a record of Venus’ convection history, as mantle convection causes time-dependent surface deformation. Venus’ mean surface age is likely in the range 300-500 Ma. The observed deformation of BV indicates that mantle convection was active over the past ∼400 Myr and provides constraints on the length scales and vertical amplitudes involved. We place constraints on Venus’ present-day internal structure and dynamics by comparing dynamical topography produced by numerical convection codes with the topography of BV.

Methods

Our approach contrasts with previous studies by using an established feature of the surface of Venus, Baltis Vallis, and its time-dependent topography instead of global spectral analysis at a single prescribed time (present-day, and its assumed corresponding simulated time in models). We simulate time-dependent stagnant-lid mantle convection on Venus with a suite of coupled interior-surface evolution models for a range of assumed mantle properties. Models are designed to reproduce as closely as possible a present-day quasi steady-state behavior and run for 1.5 Gyr, representing the state of Venus since the time of the formation of the bulk of its surface. StagYY simulates dynamic topography by calculating it from the vertical component, at the free slip surface, of the stress tensor due to the convection. StagYY includes both the effects of thermal and density variations on mantle dynamics, as well as partial melting (crust formation) and phase transitions. The viscoplastic rheology is temperature- and depth-dependent with Newtonian diffusion creep. In the current test of the methodology, only extrusive melt is considered, and the convection is forced into a stagnant-lid-like regime during the studied era by making plastic yielding impossible, as a proxy for recent evolution. Reference viscosity is varied between 10¹⁹ and 10²¹ Pa.s.

We compare the simulated topography of model BV profiles to the actual topography of BV using two metrics: the root-mean-square (RMS) height and the “decorrelation time”. The correlation between model BV topography at time τ₂ and an earlier time τ₁ is calculated. When this correlation first falls to zero, the decorrelation time is then τ₂ – τ₁. The decorrelation time is inspired by the observation of BV’s present-day uphill flow and the inference that the present-day topography must be uncorrelated. A model is considered successful if the decorrelation time is less than the surface age of Venus.

Figure2: Decorrelation time and RMS height for all models. The range for Baltis Vallis's RMS height is shown as a red shaded area.

Results

The relatively short decorrelation time required (likely 250 Myr) and the relatively low RMS topography of Baltis Vallis (217 m) both imply vigorous convection. From 14 three-dimensional mantle convection models, each initialized with different parameters, we identified two convection models that best fit our metrics. These models have a viscosity contrast ∆η of 10⁸ and 10⁷, respectively, and both have a Rayleigh number Ra of 10⁸. Although Venus’ heat flux is highly uncertain, our model fluxes are consistent with some inferred heat fluxes. Models with higher total surface heat fluxes tend to yield lower decorrelation times; our favored models have some of the highest heat fluxes. We also find that models with a higher Ra tend to have a lower RMS height.

Our favored models have vigorous convection beneath a stagnant lid, and high surface heat fluxes. The viscosity of the lower mantle in these models is 10²⁰ Pa s, roughly two orders of magnitude lower than that of Earth’s. This difference could be either the result of a warmer mantle on Venus, here due to the stagnant-lid-like insulation of the mantle leading to the increase of the interior temperature, or the presence of volatile species, for example water, if outgassing is prevented by high surface pressures. The majority of the surface heat flux is due to melt advection, indicating high rates of volcanic resurfacing. To be consistent with surface ages of volcanic activity inferred from surface observation, most of the melt should be intruded, which will likely change the thermal structure of the crust and lithosphere. Our calculated core-mantle boundary heat fluxes indicate that a dynamo should be operating, unless the core is stably stratified due to compositional layering. While current data are insufficient to test these predictions, once paired with forthcoming observations from several new Venus missions, our work will be able to bring Venus’ interior into sharper focus.

Figure 3: Radial mantle viscosity profiles (laterally averaged) for our preferred models (solid lines), shown alongside estimated viscosity-depth profiles for Earth (dashed lines) and Venus (dash-dotted lines) from other studies.

How to cite: McGregor, N., Gillmann, C., Nimmo, F., Golabek, G., Plattner, A., and Conrad, J.: Probing the viscosity of Venus's mantle using dynamic topography at Baltis Vallis, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-291, https://doi.org/10.5194/epsc-dps2025-291, 2025.

Introduction

Venus’ surface is densely populated with fractures, faults, and shear zone networks of different dimensions. This study aims to pursue a detailed investigation on large-scale shear zones of Eastern Aphrodite Terra, a high relief region on Venus that expands along the equator. The area  is radar-bright due to the presence of high fracture densities. The key feature of Eastern Aphrodite Terra is an interconnected network of straight and deep ENE-WSW to E-W trending chasmata (Fig. 1a), and large coronae, which are surrounded by deep arcuate troughs. The origin of the chasmata system is a subject of scientific debate. Herrick et al. (1989) and others proposed that chasmata are rifts, that were formed above a dynamic mantle upwelling system. Others suggested that neither divergent nor convergent tectonics occur along the troughs of Eastern Aphrodite Terra, but vertical adjustments dominate that are related to mantle up-welling and down-welling (e.g., Hansen and Phillips, 1993). In contrast, the arc-shaped and asymmetric troughs that surround the large coronae in this region were explained by convergent tectonics (e.g., Sandwell and Schubert 1992; Kenkmann et al. 2024).

Fig. 1. Diana Chasma South. A) Elevation map of Diana Chasma and adjacent area. The region of interest ROI is shown in B as original SAR data and in C) as inverted SAR data. D) Detail region of interest (ROI) of C) with location of the shear zone including dip angle and strike of the fault plane and altitude information. E) Geological map with mapped fractures, smooth patches and rugged terrain at the fault terrace. The trace of the profile is indicated. F) Fracture density map. G) Vertically exaggerated topographic profile. Note that the dip of the fault is not vertically exaggerated. H) inverted SAR of area shown in f). Hw and fw indicates hanging wall and footwall.

Observations and Measurements

• The equatorial chasmata system of Eastern Aphrodite Terra is among those regions on Venus that has the strongest relief (Fig. 1a). Most of the valleys are asymmetric in cross-section with a steeper slope of up to 40 ° inclination and a gentle slope of roughly 5° (Fig. 1g).
• We mapped distinct large-scale shear zones along the chasmata (Fig. 1c-e) and the arcuate troughs surrounding coronae in that region. The lengths of the mapped faults range between 218 km and 706 km. The faults always intersect the steep chasmata slopes.
• The faults dip at angles of 25°-37°, opposite to the slopes (Fig. 1d). Faults are strongly localized and associated with damage zones of intense fracturing (Fig. 1e-f). The fault planes themselves are partly exposed and form distinct terraces along the steep slopes (Fig. 1g).
• In close vicinity to the shear zones are patchy, small-scale hills of delicate rugged terrain, which are surrounded by radar smooth, pristine, pond like halos that partly show flow features and cover exposed parts of the shear zones (Fig. 1e, h).
• Elevation corrected radar emissivity data of the hanging wall and footwall of the shear zones, as well as of the associated rugged terrain and radar smooth planes mostly differ from each other.
• Locally, small-scale and fresh landslide deposits emanating from the steep hanging wall of the shear zone occur in the vicinity of the shear zones.

Interpretation

The occurrence of the shear zones along the steep slopes of the asymmetric chasmata suggests that they were formed by thrusting. The exposure of their fault planes, however, indicates that they got later reactivated as normal faults (Fig. 1g). The immediate proximity of landslides with shear zones points to a seismic trigger of the mass movements. The rugged and patchy hills surrounding by smooth halos are interpreted as fault breccia mixed with a fluid-like phase extruded from the faults. When the material reached the surface the low viscous material dispersed fluidly around the blocky rugged material and covered the local relief. We propose that the low viscous material is melt since a fluid phase is unlikely to occur at the present conditions on Venus. Emissivity data indicates that the extruded possible melt is compositionally different from the rugged material and from the hanging wall and footwall lithologies of the shear zones.

The melts may originate from relatively shallow crustal depths from nearby volcanic edifices and corona interiors. The shear zones serve as ascent paths for melts, lower the friction coefficients on the shear planes and with this contribute to deformation localization. Alternatively, we discuss a possible formation by frictional melting in the environment on Venus. The morphological distinctiveness and freshness of the shear zones, which are not cut by fractures, and their systematic association with delicate melt ponds and coarse breccia indicates that the shear zones are very young tectonic features that have not been geologically overprinted in any way.

References

Hansen, V. L., & Phillips, R. J. (1993). Tectonics and volcanism of east Aphrodite Terra, Venus: No subduction, no spreading. Science, 260(5107), 526–530.

Herrick, R. R., Bills, B. G., & Hall, S. A. (1989). Variations in effective compensation depth across Aphrodite Terra, Venus. Geophysical Research Letters, 16(6), 543–546

Kenkmann, T., Karagoz, O., & Veitengruber, A. (2024). Structural analysis and evolution of large Venusian coronae: Insights from low-angle faults at coronae rims. Planetary and Space Science, 250, 105955.

Sandwell, D. T., & Schubert, G. (1992). Evidence for retrograde lithospheric subduction on Venus. Science, 257, 766–770.

How to cite: Kenkmann, T. and Karagoz, O.: Neo-tectonic activity and indications for fault-melt interaction along Aphrodite Terra´s Chasmata system, Venus., EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-620, https://doi.org/10.5194/epsc-dps2025-620, 2025.

Volcanic outgassing shapes the evolution of the atmospheres of terrestrial planets, but is itself affected by the atmospheric pressure (Head and Wilson 1986, Phillips et al. 2001, Gaillard and Scaillet 2014). Outgassing can take place in form of explosive eruptions where the exsolution of volatiles from ascending magma accelerates the ascent and drives further exsolution. Observations by Pioneer Venus and Venus Express show that the abundance of SO₂ above the cloud layer (>70 km) varies by two to three orders of magnitude on timescales ranging from weeks to decades and one of the hypotheses brought forward is that explosive eruption plumes cause enhanced mixing between the SO₂-rich (>100 ppm) lower atmosphere below the clouds, and the SO₂-poor (<1 ppm) upper atmosphere above the clouds. (Esposito 1988, Marcq et al. 2013). Models of eruption plumes however show that only very intense eruptions originating at relative high elevations can reach this height (Glaze 1999). On Earth, eruptions of this intensity are rare, lower volume rate eruptions are more frequent. Plume height scales with volume rate (e.g. Glaze 1998, Airey et al. 2015). Thus there is a high probability that there are significantly more plumes that do not reach the cloud layer. Even if the SO₂ variation has a non-volcanic origin, there is evidence suggesting explosive eruptions in form of diffuse deposits that are interpreted as being formed by pyroclastic flows from collapsing volcanic ash plumes (e.g Campbell et al. 2017). A re-analysis of Venera 13 descent spectroscopic measurements suggests the presence of particles that could be volcanic ash at altitudes around 4 km (Kulkarni et al. 2025).
The frequency of such explosive eruptions is of high scientific interest. The atmospheric pressure suppresses exsolution so that the transition from an effusive to an explosive eruption requires a combination of high eruption rates and high abundance of magmatic volatiles, most importantly H₂O (Airey et al. 2015). The volatile content of Venusian magmas and outgassing efficiency is important for understanding the evolution of the atmosphere (Galliard et al. 2014). The search for locally enhanced H₂O abundance is an objective of near-infrared imaging of atmospheric windows by upcoming missions to Venus (e.g. Wilson et al. 2024) . The H₂O abundance is derived from increased extinction of thermal emission at wavelength of H₂O absorption lines relative to wavelengths with no sensitivity to H₂O (e.g. Bézard et al. 2009), thus requires at least two spectral bands.
The ash entrained in a volcanic plume is however also a significant source of extinction that can reach a large areal extent. On Venus the surface and atmospheric thermal emission radiance in near infrared window regions is sufficiently bright to be measurable through the cloud layer with optical thicknesses on the order of 20-40, however this is due to the very high single scattering albedo of cloud droplets allowing multiple scattering without significant absorptions. The single scattering albedo of volcanic ash particles is lower, resulting in a strong reduction of diffusely transmitted radiance. In large (Plinian) eruption plumes the hot ash gas mixture buoyantly rises until it reaches near ambient temperature, at which the finer ash particles spread out laterally, forming a so-called umbrella layer. The umbrella regions of eruption plume can be hundreds of km in diameter (e.g. Gupta et al. 2022) which is large compared to the blurring effect caused by multiple scattering of thermal infrared radiation within the clouds (~ 90 km) (Hashimoto and Imamura 2001). 
We model the effect of a Plinian eruption plume umbrella layer on radiance observed in the near infrared window regions using the NEMESIS radiative transfer code (Irwin et al. 2008), in order to understand under which conditions a plume would be clearly visible. This is done by introducing various amounts of ash particles with optical properties from Deguine et al. (2020) at various altitudes between the surface and cloud layer. We assume that the particles at the outside of the plume quickly equilibrate with the environment and are thus at ambient temperature. This is supported by Earth remote sensing observations of exceedingly cold brightness temperatures at the top of eruption plume umbrella layers at high altitudes (e.g. Gupta et al. 2022). If the ash layer is sufficiently opaque and at sufficiently higher altitude than the source region of the background emission there is a reduction in top of atmosphere radiance that exceeds the modulation that can be introduced by Venus cloud opacity variations. 
Under these conditions a plume can be clearly distinguished in images at just a single wavelength. This would allow imagers with a spectral filter such as Venus Express VMC, Akatsuki IR1, or Parker Solar Probe WISPR to detect such a plume while water vapor abundance measurements have so far mostly been proposed for multispectral or hyperspectral instruments. With a sufficient imaging frequency, even plumes signatures that do not exceed the typical modulation by clouds could be distinguished via their lower zonal velocity. 
The above existing and planned Envision and VERITAS datasets could detect eruption plumes but do not represent a very extensive monitoring capability due to the limited frequency and areal coverage of imaging. However, there are mission concepts focused on monitoring to search for seismic waves via airglow (e.g. Garcia et al. 2024).  Our model shows that a plume umbrella of an optical thickness of 10 at an altitude of >10 km would result in a radiance reduction of 50 % in the thermal emission background of the 1.27 µm airglow band. Mission concepts involving frequently imaging much of the nightside of Venus at a near infrared window wavelengths such as 1.27 µm present the best chance of detecting an volcanic eruption plume. 

References:

Head&Wilson1986.doi:10.1029/JB091iB09p09407 
Phillips&al.2001.doi:10.1029/2000GL011821
Gaillard&Scaillet2014.doi:10.1016/j.epsl.2014.07.009
Esposito&al.1988, doi:10.1029/JD093iD05p05267
Marcq&al.2013.doi:10.1038/ngeo1650
Glaze1999.doi:10.1029/1998JE000619
Airey&al.2015.doi:10.1016/j.pss.2015.01.009
Campbell&al.2017.doi:10.1002/2017JE005299
Kulkarni&al.2025.doi:10.1029/2024JE008728
Wilson&al.2024.doi:10.1007/s11214-024-01054-5
Bézard&al.2009.doi:10.1029/2008JE003251
Gupta&al.2022.doi:10.1038/s43247-022-00606-3
Hashimoto&Imamura2001.doi:10.1006/icar.2001.6713
Irwin&al.2008.doi:10.1016/j.jqsrt.2007.11.006
Deguine&al.2020.doi:10.1364/AO.59.000884
Garcia&al.2024.doi:10.1029/2024EA003670

How to cite: Müller, N., Kulkarni, S., Lefevre, M., Marcq, E., Garcia, R., Grott, M., and Rauer, H.: Detecting volcanic ash of eruption plumes on Venus by imaging in the near infrared windows, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1485, https://doi.org/10.5194/epsc-dps2025-1485, 2025.

Imaging of the Venus night side in the 1 µm spectral transparency “window” is a powerful tool to sound the surface mineralogy in the presence of thick clouds. Venus Monitoring Camera onboard Venus Express provided thousands of night side images covering low latitudes of the planet (30S – 30N). The first results of the geological analysis were published, for instance, by Basilevsky et al. (2012). Here we will present selected preliminary results of the geological analysis of the new data set derived in the framework of the ESA-MPS (Max Planck Institute for Solar System Research) contract (Shalygin and Shalygina, 2023).  

For the current analysis we selected several representative examples of geological units: shield plains, the lower unit of regional plains, lobate plains, and tesserae. The analysis suggests statistically significant spatial variations of the surface emissivity for the plains units likely indicating presence of non-basaltic components in the materials of lobate plains. The emissivity values of tesserae areas in Phoebe and Beta Regions show strong bimodality:  ~0.31±0.04 (3σ) for Phoebe Regio and ~0.50±0.18(3σ) for Beta Regio. If confirmed the bimodality would indicate significant compositional variations within a single morphological unit of tessera. Also, an anti-correlation between emissivity and elevation was found within specific units. This might suggest both emissivity changes with altitude as well as an artefact of not completely corrected atmospheric effects like temperature lapse rate and gas absorption coefficient, which role requires additional sensitivity studies.

References

A.T. Basilevsky, E.V. Shalygin, D.V. Titov et al. Geologic interpretation of the near-infrared images of the surface taken by the Venus Monitoring Camera, Venus Express. Icarus 217, pp 434-450, 2012.

E. Shalygin and O. Shalygina. Surface and cloud properties from VMC/Venus Express observations. Final Report (VMC-MPS-FR), ESA Contract 4000126833/18/NL/IB/gg, 2023.

How to cite: Titov, D., Ivanov, M., Basilevsky, A., and Roos, M.: Surface mineralogy from the Venus Monitoring Camera observations: preliminary results from the re-processed images in 1 micron transparency “window”, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-275, https://doi.org/10.5194/epsc-dps2025-275, 2025.

Understanding the geological evolution and current activity of Venusian volcanoes is essential for constraining the planet's resurfacing history and interior dynamics. This study presents a focused multi-dataset remote sensing analysis of Idunn Mons, one of Venus’ most prominent volcanic edifices, leveraging multi-angle Synthetic Aperture Radar (SAR) data alongside dielectric property maps, topographic data, and VIRTIS-derived spectral emissivity layers.

The core objective of this investigation is to detect anisotropic radar backscatter patterns caused by slope orientations, surface textures, and material flow directions on Idunn Mons, while also identifying regions of potential recent volcanic resurfacing. Aligned and co-registered left-looking and right-looking Magellan SAR images are processed to calculate a Radar Asymmetry Index (RAI), differentiating east- and west-facing slopes and highlighting variations potentially linked to surface anisotropy or resurfacing events.

These radar datasets are subsequently stacked with dielectric maps, GTDR topography, and VIRTIS FFT emissivity layers to create a multi-dimensional dataset. Unsupervised clustering techniques, including Self-Organizing Maps (SOM) and K-means clustering, are applied to this dataset both with and without the RAI as an input parameter. The study evaluates the effectiveness of these clustering methods in delineating volcanic flow textures, unit boundaries, radar-dark backscatter zones, and potential volcanic features.

Preliminary results demonstrate that integrating RAI enhances the detection of flow-like structures and flank asymmetries, while clustering outputs overlaid on topography and slope direction maps reveal correspondences between cluster classes and geomorphological features such as radial flows, summit regions, and dielectric anomalies. The analysis further explores potential spatial relationships between low backscatter zones and high emissivity areas detected by VIRTIS, which may indicate recent or ongoing volcanic activity.

This study advances geological mapping methodologies for Venus by integrating radar asymmetry analysis with multi-layered clustering-based terrain segmentation. The findings contribute to refining remote sensing techniques for planetary surfaces lacking in-situ observations and provide valuable insights for future mission planning and Venusian volcanology research.

How to cite: Garg, S. and Woehler, C.: Multi-Dataset Analysis of Idunn Mons: Integrating SAR Look Angle, Dielectric, Topography, and Emissivity Data for Volcanic Terrain Mapping on Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-883, https://doi.org/10.5194/epsc-dps2025-883, 2025.

Introduction:

The existence of lava tubes on planetary bodies has long been a subject of interest in planetary geology, with confirmed instances on the Moon, Mars, and Earth [1,2]. These subsurface cavities not only provide insights into volcanic processes but also represent primary targets for the Subsurface Radar Sounder (SRS) instrument planned for the EnVision mission to Venus. The SRS aims to penetrate the planet's surface to depths of several hundred meters, potentially revealing the internal structure of lava tubes and other underground features [3]. However, until now, the presence of lava tubes on Venus has remained speculative due to limitations in observational data [4].

We present the first compelling evidence for the existence of lava tubes on Venus, based on an extensive analysis of pit alignments on Venusian large volcanoes. Our investigation focused on volcanoes larger than 100 km in diameter [5], utilizing radar imagery and topographic data from past Venus missions.

Results:

Our survey revealed four distinct instances of sinuous pit chains that do not appear to be associated with tectonic extensional structures. These alignments exhibit characteristics consistent with the collapse features observed above lava tubes on other planetary bodies. Key findings include: (i) morphometry: in plan-view the identified pit alignments display a curvilinear arrangement, typical of collapsed sections of lava tubes. Higher sinuosity has been observed for these instances compared to a sample of pit alignments produced by tectonic collapses; (ii) dimensions: pits’ width and depth cannot exceed those of the underlying lava tube, while pits that form on tectonic structures show a correlation between their diameter and depth; (iii) geological context: all four instances are not only located on the flanks of shield volcanoes, in areas characterized by extensive lava flows which is consistent with the formation environment of lava tubes on other planetary bodies, but they also develop in a direction consistent with the slope of the terrain on which they were observed, thus consistent with the hypothesis that they are the product of lava flowing on an inclined surface. Additionally, the inferred geometry of the cavities matches the crusting-over formation process typically associated with non-inflating lava tube development [6,7]. This process involves the solidification of the upper layer of a lava flow while the underlying molten lava continues to drain, leaving behind a hollow conduit. However, the volumes estimated for the Venusian lava tubes based on the visible extent of the pit alignments and assuming continuity between collapse features, are comparable to those observed on the Moon (fig.1) , implying the presence of cavities larger than those observed on Earth [1].

Figure 1. Collapse width W versus linear volume V₁ expressed in a logarithmic plot, along with power laws trend lines for each planetary body and for the whole dataset (black line) are shown.

Conclusions:

This study presents the first observational evidence for the existence of lava tubes on Venus, significantly expanding our understanding of the planet's volcanic processes and geological evolution. The discovery of these structures not only enhances our knowledge of planetary speleogenesis but also has implications for future exploration strategies. The characteristics of the observed Venusian lava tubes, particularly their large scale, suggest that Venus may host some of the most extensive subsurface cavities in the solar system. However, the limitations in current observational data emphasize the need for future high-resolution imaging missions to Venus to fully map and characterize its lava tube systems. As we continue to explore the volcanic landscapes of Venus, these newly discovered lava tubes may help constrain models of the planet's thermal and tectonic evolution, and offer exciting possibilities for understanding the planet's past and present conditions.

Acknowledgement: B.D.T. is supported by the European Union – NextGenerationEU and by the 2023 STARS Grants@Unipd programme HECATE.

References: [1] Sauro et al., Earth-Science Reviews 209 (2020): 103288. [2] Carrer et al., Nat. Atro. 8.9 (2024): 1119-1126. [3] Bruzzone et al. EnVision Int. Venus Sci. Works. (2023). [4] Carrer et al., IEEE Tran. on Geos. Rem. Sens. (2024). [5] Hahn and Byrne. JGR: Planets 128.4 (2023): e2023JE007753. [6] Hon et al., Hawaii. Geol. Soc. Am. Bull. 106 (3), 351–370, (1994). [7] Peterson, et al., Hawaii. Bull. Volcanol. 56 (5), 343–360, (1994).

How to cite: De Toffoli, B., Pozzobon, R., Carrer, L., and Sauro, F.: First Evidence of Lava Tubes on Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-686, https://doi.org/10.5194/epsc-dps2025-686, 2025.

Introduction

Venus is a volcanic wonderland—replete with lava channels at scales unseen on any other planetary body. Some lava channels on Venus resemble those seen on Mars and Earth’s Moon. For example, Venus hosts sinuous rilles with lengths of ~10–300 km and widths up to several km. However, many channels look more like the fluvial features observed on other terrestrial planets. Canali are long, narrow channels, over ~1 km wide, ~24 m deep, and ~500 km long on average. One canale, Baltis Vallis, is ~6,800 km long, making it the longest channel found in the Solar System. The goals of our project are (1) to better understand the formation of these enigmatic features and (2) to help prioritize follow-up investigations by future missions.

Importance of Carbonatite Lavas in Outgassing Venus’s Modern-day Atmosphere

Venus diverged from Earth’s evolutionary path through the development of a CO₂-dominated atmosphere, though studies dispute whether this atmosphere emerged immediately after accretion or following a protracted period of surface habitability. Observations of widespread volcanic features suggest that volcanic outgassing may have played a pivotal role in the transformation of Venus. However, basaltic lavas would only outgas a minor fraction of the CO₂ in the current atmosphere from the volume of the current crust. Here we show that carbonatite lavas possess the unique properties required to (mechanically) erode the canali. Our results suggest that eruption of these carbonatites may have delivered a total mass of CO₂ comparable to that of the modern atmosphere, potentially resolving one challenge to the formation of Venus’s atmosphere within the recent past.

Eruption Properties Required to Form the Venusian Sinuous Rilles

Depth profiles of lava channels reveal whether thermal or mechanical erosion is the dominant process. Canali appear to have roughly constant depths along their exceptional lengths, which is most consistent with mechanical erosion. In contrast, thermal erosion likely formed the sinuous rilles, which exhibit depths that decrease along track. For example, one previous study showed that tholeiitic basalt could form some rilles. They calculated initial lava thickness of ~2–6 m and eruption durations between several months and a few years. We use our models to test the eruption properties required to form the sinuous rilles with various types of basaltic and komatiitic lavas. Using the Markov Chain Monte Carlo method, we compute the statistical probability distributions for these properties, considering the uncertainties on several model parameters.

Implications for Venus Exploration

Upcoming missions to Venus will provide a generational leap in our understanding of lava channels. The EnVision and VERITAS orbiters will return higher-resolution images and topography of canali and rilles. Multispectral images may allow us to infer the composition of channel-forming lavas. Carbonatite on Venus may weather to form patchy coatings of anhydrite in the presence of SO₂. Carbonatites and sulfates would exhibit low NIR emissivity. Laboratory studies of their emissivity under Venus’s atmospheric and temperature conditions should be performed to distinguish them from other weathering products. The subsurface radar sounder on EnVision may also elucidate the structure of lava flows in and around these channels. Ultimately, the volumes of lava that formed canali and rilles might be small relative to that of the crust. However, these channels can reveal processes that shaped the big-picture evolution of Venus over time, and in turn how Venus serves as an exemplar for the evolution of terrestrial (exo)planets.

(Artist's impression of carbonatite lava forming canali on Venus, by Hernán Cañellas)

How to cite: O'Rourke, J., Trussell, A., Williams, D., Flynn, I., Black, B., and Borrelli, M.: Formation of Lava Channels on Venus: Implications for Eruption Properties and Atmospheric Outgassing, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1203, https://doi.org/10.5194/epsc-dps2025-1203, 2025.

The modern atmosphere of Venus shows a substantially lower abundance of water vapour [1-3] and a high deuterium to hydrogen ratio (D/H) compared to Earth [3, 4]. This high D/H ratio suggests a significantly larger initial water reservoir than today. Some climate modelling studies suggest that early Venus might have had an initial benign climate, with the dayside cloud-albedo feedback supporting early and prolonged surface Habitability – also based on the planet’s slow-rotation [5, 6, 7]. According to this hypothesis, this benign early climate is theorised to end by large-scale volcanism in the form of multiple large igneous provinces, eventually leading to the present runaway greenhouse state we currently observe on modern Venus [8]. Water vapour photodissociation and preferential loss of the lighter hydrogen would explain the observed D/H ratio [9]. Other climate modelling studies claim that warming from nightside stratospheric clouds could prevent water condensation in the first place [10].

Assuming surface water condensation from the steam atmosphere in the first place, we simulate a hypothetical ocean on Venus at 2.9 Ga by using a 3D General Circulation model (GCM). We use the 3D GCM ROCKE-3D (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics), developed at the NASA Goddard Institute for Space Studies [11]. The simulations use a spatial resolution of 4ºx5º (latitude x longitude), a 40-layer atmosphere (with a top pressure: 0.1-hPa) and a 13-layer fully dynamic ocean [12] coupled to the atmosphere. For the reference simulation, we select a modern Venus topography following the NASA/Magellan archive. We simulate a 310-m global equivalent layer (GEL), covering ~60% of the surface of Venus. Ocean volume is 1.4 x 10¹⁷ m³, one order of magnitude below that of modern Earth’s Ocean [5]. We set insolation to 2001 W/m² or 1.47 times that of modern Earth, representing conditions at 2.9 Ga. The atmospheric composition was set to be Archean Earth-like (1.013 bar N₂, 400 ppm CO₂, 1 ppm CH₄) [6]. Other planetary parameters follow the modern values of Venus’s surface gravity, radius, obliquity, eccentricity and rotation rate (retrograde slow-rotator: -243 days) [5].

We will discuss the main physical oceanographic parameters (e.g., potential temperature, salinity, potential density) and ocean circulation. Our simulations point to the existence of a significant monthly-long diurnal cycle, allowing for the development of a considerable mixed layer depth at the equator during the nighttime. This diurnal cycle results in the inversion of the equatorial surface current, from a -125 cm/s westward at midday to 50 cm/s eastward at the evening terminator. The highly saline Southern Ocean is controlled by a mass balance that favours evaporation, and is influenced by a limited exchange due to the presence of a strait-like feature preventing denser water to cross the sill. In addition, the model shows the development of a complex «meridional overturning circulation», controlled by the bathymetry and a southern «closed» basin. We will compare this ocean circulation results with a simulation of a deeper ocean on the paleo-Venus, assuming a 1000-m GEL with a modern Venus-like topography.

Moreover, we will study the impact of the paleo bathymetry/topography in the ocean circulation and tidal dissipation. Initial simulations are based on the NASA/Magellan altimetry database. However, modern volcanic rises might not have been present in the early Venus. Venusian tides are simulated using the portable Oregon State University Tidal Inversion Software (OTIS), a model extensively used for deep-time, present-day and future tides on Earth [13 – 16] and on Venus with a modern topography [17]. We will draw conclusions for the importance of studying ocean circulation, landmass configuration, and interactions between atmosphere-ocean for Earth-sized exoplanets located in the vicinity of the inner edge of the Habitable Zone.

References: [1] Bézard B., et al.,2011.Icarus.216:173; [2] Cottini et al.,2015. Space Sci.113:219; [3] Encrenaz T, et al.,2015. Space Sci.113:275; [4] Krasnopolsky V, et al.,2013.Icarus.224:57; [5] Way M.J., et al.,2016.GRL.43; [6] Way M.J. & Del Genio A.D. (2020).JGR:Planets.125; [7] Yang J, et al., 2014, ApJL., 787, L2 [8] Way M, et al.,2022. Sci. J.3:92; [9] Chaffin M, et al.,2024.Nature.629:307; [10] Turbet M., et al.,2021.Nature.598:276; [11] Way M.J., et al.,2017.ApJS.213:12; [12] Russell G.L., et al.,1995.Atmos-Ocean.33:683 ; [13] Egbert, G.D., et al., 2004, JGRC, 109, C03003 ; [14] Green, J., et al., 2017, E&PSL, 461,46 ; [15] Green, et al., 2018, GeoRL, 45, 3568 ; [16] Wilmes, S.-B., 2017, JGRC, 122, 8354 ; [17] Green, et al., 2019, ApJL,876, L22.

Funding: DQ acknowledges FCT a PhD fellowship 2023.05220.BD

How to cite: Quirino, D., Way, M. J., Green, J. A. M., Duarte, J. C., and Machado, P.: Ocean circulation and tides on a temperate paleo-Venus, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1577, https://doi.org/10.5194/epsc-dps2025-1577, 2025.