The cause of the inhomogeneous near-ultraviolet absorption observed in the upper clouds of Venus remains a key question in Venusian research. One possible candidate in the literature is ferric chloride. The absorption spectrum of ferric chloride currently in use by models uses ethyl acetate as a solvent and does not reproduce the absorption features observed on Venus. The study of the optical properties and chemistry of ferric chloride in the sulphuric acid cloud droplets is required to draw valid conclusions regarding its suitability as a candidate for the near-UV absorption.

In this study, we measure the absorption spectrum of ferric chloride in sulphuric acid from 200 – 600 nm at a range of temperatures and measure the rate of conversion of the ferric chloride ions into ferric sulphate ions. We then use the resulting ferric chloride absorption coefficients in a 1D radiative transfer model and estimate the required concentration of ferric chloride in the clouds to be 0.6 – 0.9 wt% in the mode 1 (~0.3 µm radius) cloud droplets to match observations. We also predict the atmospheric concentrations of ferric chloride formed from the reaction of iron ablating from cosmic dust entering Venus’ atmosphere around 120 km with hydrogen chloride emitted by volcanic activity, and estimate the accumulation timescale of ferric chloride to produce the required concentrations in the clouds.

How to cite: Egan, J., Feng, W., James, A., Manners, J., Marsh, D. R., and Plane, J. M. C.: Laboratory studies and modelling of ferric chloride as the cause of the anomalous UV absorption in the Venusian atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16898, https://doi.org/10.5194/egusphere-egu24-16898, 2024.

Until now, the Venus PCM (Planetary Climate Model) was using precomputed tables for the distribution of the solar heating rates in the atmosphere of Venus. A new scheme is now implemented to compute online the radiative transfer of the solar flux, which allows more flexibility to study sensitivity to opacity sources. We have investigated the sensitivity of the temperature and circulation of the Venusian cloud region to the distribution of the UV absorber. Different vertical distributions of the UV absorber, as well as variations of this along latitudes, have been tested, and comparison is discussed of the vertical profile of computed solar heating rates, temperature distribution in the cold collar region, as well as the resulting mean zonal wind field.

How to cite: Han, P. and Lebonnois, S.: Influence of the UV absorber distribution on the temperature and circulation ofthe Venusian cloud region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16505, https://doi.org/10.5194/egusphere-egu24-16505, 2024.

EnVision radio science investigation will deepen our understanding of Venus’ gravity, interior structure and atmospheric properties. To address these scientific questions, a two-way link communication (configuration X/X/Ka-band) is established with the ESA ESTRACK ground stations enabling precise orbit determination (POD) during the science phase. An accurate modeling of the spacecraft’s dynamics, including the atmospheric drag acceleration, is key for retrieving EnVision’s trajectory and constraining Venus’ gravity field, tides and orientation parameters.

Dedicated radio occultation campaigns are designed to characterize electron density profiles in the ionosphere and atmospheric density, pressure and temperature in the mesosphere and upper troposphere of Venus. Furthermore, an accurate POD of the spacecraft also provides complementary information on the atmospheric density at the altitudes crossed by the probe, extending the science return of the EnVision mission.

The atmospheric drag perturbation strongly affects spacecraft trajectories that are characterized by a pericenter altitude above Venus’ surface of less than 220 km. By accounting for different Venus’ atmospheric models, e.g., the Venus Climate Database (VCD) and the Venus Global Reference Atmospheric Model (Venus-GRAM), we investigate the impact of potential errors and uncertainties in the predicted atmospheric properties on the orbit evolution of the spacecraft. We note significant inconsistencies between Venus’ atmospheric models at the spacecraft altitudes including atmospheric density differences of more than 200%. These discrepancies may be representative of the current knowledge of Venus’ upper atmosphere and thermosphere. Thus, we carried out a perturbative analysis of the dynamical forces by introducing a mismodeling in the atmospheric density profiles. We assumed the VCD for the simulation of the radio tracking measurements and we included as a priori model in the estimation process the Venus-GRAM. By developing a batch sequential filter that adjusts a set of atmospheric density scale factors, we compensated for the mismodeling and improved the quality of the dynamical model and of the orbit determination. The proposed approach enables an estimation of the atmospheric density at the spacecraft altitudes with an accuracy of 25% and accuracies in the orbit reconstruction of 1-2 m, 30-40 m and 20-30 m in the radial, transverse and normal directions.

How to cite: Gargiulo, A. M., Genova, A., Petricca, F., Del Vecchio, E., Andolfo, S., Torrini, T., Rosenblatt, P., Lebonnois, S., Marty, J.-C., and Dumoulin, C.: Estimation of Venus' atmospheric density through EnVision precise orbit determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13314, https://doi.org/10.5194/egusphere-egu24-13314, 2024.

High-resolution runs of the Venus PCM (1.25° in longitude and latitude) successfully simulated Venus atmospheric superrotation. The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 days and 8.5 days. The simulation successfully reproduces long-term quasi-periodic oscillation of the zonal wind and primary planetary-scale wave seen in observations. These oscillations are obtained with a period of about 163-222 days close to the observations. The Rossby waves show robustness in wave characteristics and angular momentum transport due to Rossby-Kelvin instability by comparing the 5.65-day wave with the 5.8-day wave simulated by another Venus GCM, AFES-Venus. Similarities are also evident between the 8.5-day wave in our simulation and the 7-day wave obtained in AFES-Venus. Furthermore, the long-term variations in angular momentum transport indicate that the 5.65-day wave is the dominant factor of the oscillation on the superrotation, and the 8.5-day wave is the secondary. When the 5.65-day wave grows, its angular momentum transport is enhanced and accelerates (decelerates) the lower-cloud equatorial jet (cloud-top mid-latitude jets). Meanwhile, the 8.5-day wave weakens, reducing its deceleration effect on the lower-cloud equator region. Consequently, this flattens the background wind and weakens instability, leading to the decay of the 5.65-day wave. And vice versa when the 5.65-day wave is weak.

How to cite: Lai, D., Lebonnois, S., and Li, T.: Planetary-scale wave study in Venus cloud layer, simulated by the Venus PCM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17524, https://doi.org/10.5194/egusphere-egu24-17524, 2024.

The investigation into Venus's atmosphere has highlighted deficiencies in photochemical models when it comes to explaining the distribution of trace gas species, particularly crucial elements like CO and OCS, which play a vital role in Venus's sulfur cycle and cloud formation.

To gain a comprehensive understanding of the abundance and variability of these trace gases ahead of the DaVinci probe's descent, we initiated an observational study using NASA's IRTF telescope equipped with the high-resolution ISHELL spectrometer. Conducted from June 11 to June 30, 2023, our study involved capturing K, H, and J-band spectra of Venus's night side. We employed the SMART software to calculate synthetic spectra, considering various gas abundances and emission angles.

With our high-resolution spectral data (R=λ/Δλ~25,000), we successfully mapped the abundances of CO, H2O, and OCS in the equatorial region, revealing both daily and latitudinal variations. Our focus was on examining the delicate balance between chemistry and transport, evident in the observed anti-correlation between OCS and CO abundance with cloud opacity.

Through near-infrared observations, this study aims to unravel the intricate interplay between atmospheric dynamics and chemical reactions in Venus's cloud formation. By providing insights into observed cloud patterns and elucidating the relationship between atmospheric chemistry, dynamics, and cloud creation on Venus, we contribute crucial parameters to refine existing photochemical models.

How to cite: Liao, T.-J., Young, E., Bullock, M., crisp, D., and Yung, Y.: Unraveling Venus's Atmospheric Composition: Insights into CO, H2O, and OCS Abundances through Observations and Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10655, https://doi.org/10.5194/egusphere-egu24-10655, 2024.

The Venusian atmosphere has everything to be an exciting natural sulfur laboratory. In addition to relatively high concentrations of sulfur dioxide, suitable conditions in the atmosphere make both thermo- and photochemical reactions possible, allowing for complex chemical reactions and the formation of new sulfur containing compounds. These compounds could explain or contribute to the enigmatic 320-400 nm absorption feature in the atmosphere. One of the proposed absorbers is polysulfur compounds. While some experimentally obtained UV-VIS spectra have been published, studying the different polysulfur species individually is extremely difficult due to the reactive nature of sulfur. In this work UV-VIS spectra for polysulfur species S₂ to S₈ were simulated using the nuclear ensemble approach to determine if they fit the absorption profile of the unknown absorber.

Geometries were optimized at the ωB97X-D/aug-cc-pV(T+d)Z level of theory, with the S₂, S₃, and S₄ structures also being optimized at the CCSD(T)/aug-cc-pV(T+d)Z level of theory. For the lowest energy isomers UV-VIS spectra were simulated using a nuclear ensemble of 2000 geometries, with vertical excitations calculated at the EOM-CCSD/def2-TZVPD or the ωB97X-D/def2-TZVPD levels of theory.

The simulated UV-VIS spectra for the smaller species were in quite good agreement with experimental results. Two different molecules were identified with substantial absorption cross sections in the range of the unknown absorber: The open chain isomer of S₃, and the trigonal isomer of S₄ However, the mixing ratios of these species in the Venusian atmosphere are also needed to make a more conclusive statement. Other polysulfur compounds have insignificant absorption cross sections in the 320-400 nm range and can therefore be excluded.

The calculated absorption cross sections can be used to calculate photolysis rates, which can be straight away added to atmospheric models of Venus. In addition, this work will help future space missions to Venus, for example by focusing their search for the unknown absorber.

How to cite: Skog, R., Frandsen, B., and Kurtén, T.: Simulating UV-VIS Spectra for Polysulfur Species in the Venusian Atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8798, https://doi.org/10.5194/egusphere-egu24-8798, 2024.

Venus is a natural laboratory to study the atmospheric circulation on a slowly rotating planet. The dynamics of its upper atmosphere (60-120 km) is a combination of retrograde zonal wind found in the lower mesosphere and solar-to-antisolar winds that characterize the thermosphere, and it is subject to a strong turbulence and a dramatic variability both on day-to-day as well as longer timescales. Moreover, several wavelike motions with different length scales have been detected at these altitudes within and above the clouds and they are supposed to play an important role in the maintenance of the atmospheric circulation. The basic processes maintaining the super-rotation (an atmospheric circulation located at the clouds level and being 80 times faster than the rotation of the planet itself) and other dynamical features of Venus circulation are still poorly understood [1].

Different techniques have been used to obtain direct observations of wind at various altitudes: tracking of clouds in ultraviolet (UV) and near infrared (NIR) images give information on wind speed at cloud top (~70 km altitude) [2] and within the clouds (~61 km, ~66 km) [3], while ground-based measurements of doppler-shift in CO₂ band at 10 μm [4] and in several CO (sub-)millimeter lines [5,6] sound thermospheric and upper mesospheric winds, showing a strong variability.

In the mesosphere, at altitudes where direct observations of wind are not possible, zonal wind fields can be derived from the vertical temperature structure using the thermal wind equation. Previous studies [7,8,9] showed that on slowly rotating planets, like Venus and Titan, the strong zonal winds at cloud top can be successfully described by an approximation of the Navier–Stokes equation, the cyclostrophic balance in which equatorward component of centrifugal force is balanced by meridional pressure gradient.

We will present zonal thermal winds derived by applying the cyclostrophic approximation from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) temperature retrievals. VIRTIS was one of the experiments on board the European mission Venus Express [10]. For this study, we will analyze the complete VIRTIS dataset acquired between December 2006 and January 2010 [11,12].

References

[1] Sanchez-Lavega, A. et al. (2017) Space Science Reviews, Volume 212, Issue 3-4, pp. 1541-1616.

[2] Goncalves R. et al. Atmosphere, 12:2., 2021. doi: 10.3390/atmos12010002.

[3] Hueso, R. et al. (2012) Icarus, Volume 217, Issue 2, p. 585-598.

[4] Sornig, M. et al. (2013) Icarus 225, 828–839.

[5] Rengel, M. et al. (2008) PSS, 56, 10, 1368-1384.

[6] Piccialli, A. et al. A&A, 606, A53 (2017) DOI: 10.1051/0004-6361/201730923

[7] Newman, M. et al. (1984) J. Atmos. Sci., 41, 1901-1913.

[8] Piccialli A. et al. (2008) JGR, 113,2, E00B11.

[9] Piccialli A. et al. (2012) Icarus, 217, 669–681

[10] Drossart, P. et al. (2007) PSS, 55:1653–1672

[11] Grassi D. et al. (2008) JGR., 113, 2, E00B09.

[12] Migliorini, A. et al. (2012) Icarus 217, 640–647.

How to cite: Piccialli, A., Grassi, D., Migliorini, A., Politi, R., Piccioni, G., and Drossart, P.: Zonal winds in Venus mesosphere from VIRTIS/VEx temperature retrievals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18366, https://doi.org/10.5194/egusphere-egu24-18366, 2024.

The next ESA mission to Venus, EnVision, aims to study the planet as a whole, including its various constituting parts as well as their interactions and coupling processes. Several instruments will therefore compose the payload: a synthetic aperture radar (VenSAR, NASA), a subsurface radar sounder and a suite of three spectrometers (VenSpec) will be embedded, and a radioscience experiment will be implemented. Among them, the UV channel of the spectrometer suite, VenSpec-U, will observe the atmosphere above the clouds and will focus on the characterisation of the sulphured gases SO₂ and SO, the monitoring of the unknown UV absorber and dynamical processes. These four topics have been identified as the main science objectives of the instrument and have driven the elaboration of a preliminary design based on the requirements (e.g. spectral range, spectral and spatial resolution) that were formulated with respect to these goals.

The compliance of the current design with respect to these requirements, regarding in particular the precision of the retrieved science data, can then be assessed. Sensitivity studies are therefore performed using the Radiative Transfer Model (RTM), updated from the one used for SPICAV-UV/Venus Express retrievals (Marcq et al., 2020), that allows to link atmospheric features and UV reflectance spectra. Two types of perturbations are considered : errors of random nature arising from the presence of noise on the signal, or systematic errors caused by various effects that induce biases on the measurements. The first ones can be characterised through the influence of the Signal-to-Noise Ratio (SNR) on the uncertainties associated to each retrieved parameter through the fitting algorithm. Limits in terms of SNR can then be defined in order to ensure the compliance with the specifications. The second ones are referring to the impact of biases on the retrievals’ accuracy, and evaluate more specifically the effects of the similarities between the spectral characteristics of these biases and those of the atmospheric components aiming to be detected. The implemented method is based on the Effective Spectral Radiometric Accuracy (ESRA) requirement, previously defined within the framework of the ESA Sentinel missions. It allows to study biases independently as well as potential compensations, so that allowable envelopes of residual errors can then be estimated for each of the considered biases.

How to cite: Conan, L., Marcq, E., Lustrement, B., Rouanet, N., Vandaele, A. C., and Helbert, J.: Sensitivity studies for the VeSUV/VenSpec-U instrument onboard ESA’s EnVision mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16442, https://doi.org/10.5194/egusphere-egu24-16442, 2024.

Previous studies have inferred volcanic activity on Venus from indirect evidence, including variations in atmospheric composition and thermal emissivity data [1, 2, 3]. More recently, a study hypothesized ongoing volcanic activity on Venus, evidenced by a volcanic vent that collapsed between two different Magellan observing cycles [4]. Expanding upon this premise, we are investigating the surface geology of Venus using the extensive radar and altimetric data acquired by the Magellan spacecraft.

In particular, by properly processing the SAR images, we are conducting a detailed geomorphological analysis of Venus' surface, in order to identify and characterize various surface morphologies. Additionally, the altimetric data provided valuable insights into the topographical variations across Venus, further contributing to the geomorphological assessment.

Our research not only enhances the understanding of the geology of Venus but also underscores the significance of radar imaging in the study of planetary surfaces, where no other imaging techniques are available. The findings highlight the crucial role of continued exploration of Venus, which could be greatly advanced by upcoming missions such as VERITAS and EnVision [5, 6]. Equipped with superior radar technology, these missions are expected to provide images of Venus's surface at an unprecedented resolution and signal-to-noise ratio, far surpassing that of the Magellan SAR, thus enabling a more detailed characterization of Venus's surface morphology.

References

1. Truong, N. & Lunine, J. Volcanically extruded phosphides as an abiotic source of Venusian phosphine. Proceedings of the National Academy of Sciences 118, e2021689118 (2021).

2. Esposito, L. W. Sulfur dioxide: Episodic injection shows evidence for active Venus volcanism. Science 223, 1072-1074 (1984).

3. Smrekar, S. E. et al. Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science 328, 605-608 (2010).

4. Herrick, R. R. & Hensley, S. Surface changes observed on a Venusian volcano during the Magellan mission. Science, eabm7735 (2023).

5. Hensley, S. et al. VISAR: Bringing Radar Interferometry to Venus. In Proceedings of International EnVision Venus science workshop, Berlin, Germany (2023).

6. Ghail, R. C. et al. VenSAR on EnVision: Taking earth observation radar to Venus. International journal of applied earth observation and geoinformation 64, 365-376 (2018).

Acknowledgments

G.M., D.S., and M.M. acknowledge support from the Italian Space Agency (2022-15-HH.0).

How to cite: Sulcanese, D., Mitri, G., and Mastrogiuseppe, M.: Investigating the volcanic activity on Venus with Magellan data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8135, https://doi.org/10.5194/egusphere-egu24-8135, 2024.

The NASA Magellan Mission (1990 to 1994) produced a valuable resource that planetary geologists continue to use three decades later to unravel the geological characteristics of Venusian Large Igneous Provinces. The ability to be the first to map the surface of Venus is a powerful engagement tool to inspire the next generation of planetary geologists, as illustrated by the size of the Mount Royal University (MRU) Venus geological mapping team (now 25, nearly ¼ of the MRU Geology Major program). MRU is a public undergraduate university. Students are recruited out of 1^st and 2^nd year courses. In year one (Y1) of the research program students learn how to use the ArcGIS software while being introduced to the geological features of Venus as they map their quadrant, in Y2 or Y3 the students present a poster at an internal research day. The goal by Y4 is for these students to publish a peer-reviewed journal article. Currently one student who ran into pandemic roadblocks through high school could be published while she upgrades her marks, before she is in the MRU Geology Major Program. Such opportunities could prove to be incentives to guide other students past similar roadblocks (we will start working with local junior and high school students in the near future). Collectively we are working towards completing the geological map of the Henie Quadrangle (V-58, south Venus). Detailed mapping (at 1:500,000) revealed that lava canali extend across the entire quadrangle, with evidence for at least three generations of canali. Three canali originate from corona features (e.g. the circumferential dykes around Fotla Corona) suggesting that some canali may be linked to corona formation. The orientation of compressional wrinkle ridges (WR) in northern Henie suggest that these WRs were formed due to strain associated with the formation of the Artemis tectonomagmatic feature which is directly north of Henie. Artemis is possibly the largest such feature in the Solar System. The extent of the Artemis influence is being constrained across the Henie Quadrangle. The source of strain that formed a differently oriented WR swarm to the south of Henie is unknown. There is no evidence for the strain localization into master faults that we see on Earth. More work is needed to develop a model for the formation of the paired Latmikaik-Xacau Coronae and the associated Tellervo Chasma, Sunna-Laverna Dorsae and the Sonmunde-Mdeb-Arubani Flucti. A fissure eruption out of the Sunna Dorsa is proposed as the origin for the surrounding Arubani Fluctus.      

How to cite: Boggs, K., Shackman, J., Demorcy, J., Pendleton, C., Hall, J., Chowdhury, M., Bley, H., Varga, E., Shustova, J., Dear, B., Fontaine, P., Dhami, L., Herrington, S., Ernst, R., El Balil, H., Bethell, E., and Hamner, S.: Henie Quadrangle (V-58, Southern Venus); Large Igneous Province Features, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14443, https://doi.org/10.5194/egusphere-egu24-14443, 2024.

The dynamic regime prevailing in the mantle of present-day Venus is still unknown. The surface of Venus seems uniformly quite young; it has  been proposed that it was due to a catastrophic resurfacing 150-700 Ma, and that the planet was in a stagnant lid regime since. Indeed, Magellan observations have failed to reveal a continuous set of accretion ridges and subduction zones, signatures of plate tectonics. But subduction features (trench, elastic bulge) are present in a number of localized spots, for exemple around two of the largest coronae, Artemis and Quetzelpetlal. There, subduction would be mainly by roll-back and could have been induced by the impingement of a mantle plume under the lithosphere, as predicted by our recent fluid dynamics laboratory experiments. Further analysis of our experiments suggest that subduction would be facilitated by the presence of a few % of a liquid phase in the asthenosphere. Melt would be most likely for the Venusian case, as anyway hinted by the amount of volcanic features on the surface of the planet. The experimental scaling laws further suggest that roll-back and subduction could be quite fast (10 cm/yr) because of the old age of the subducting lithosphere and the transformation to eclogite of the basaltic crust. This is turn would generate the rapid opening of a back-arc basin. Laboratory experiments show that for Venus temperature conditions, the produced crust and lithosphere could be quite disorganized with a contorted spreading center, large transforms and microplates. Moreover, the buoyancy of the newly created plate would cause it to remain quite elevated compared to the surrounding plains. Hence, inspection of the topography of Venus suggests several new plates created by subduction: beside the interior of Artemis coronae, Enyo Fossae and Asthik Planum could be plausible candidates. 

How to cite: Davaille, A.: Signatures of a regime of episodic localized subduction: from laboratory experiments to Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16255, https://doi.org/10.5194/egusphere-egu24-16255, 2024.

With the selection of multiple missions to Venus by NASA and ESA that are planned to launch in the coming decade, we will greatly improve our understanding of Venus. However, none of these missions have determining the seismicity of the planet as one of their primary objectives. Nevertheless, constraints on the seismicity remain crucial to understand the tectonic activity and geodynamic regime of the planet and its interior structure. 

Funded by the International Space Science Institute (ISSI) in Bern, Switzerland, we have gathered an interdisciplinary team of experts in seismology, geology, and geodynamics to assess the potential seismicity of Venus, specific regions that could be seismically active at present, and the methods to detect them.

Here, we present the findings from our second ISSI team meeting (January 29 - February 2, 2024), aiming to review knowledge on Venus's seismicity and interior and identify the best approaches for future missions. We present the feasibility, advantages, and disadvantages of different seismic observation techniques on the surface (e.g., broadband seismometers, distributed acoustic sensing methods), from a balloon (acoustic sensors), and from orbit (airglow imagers). We make a recommendation for the instrumentation of a future seismology-focused mission to Venus. 

We also suggest target regions with a high likelihood of significant surface deformation and/or seismicity. These targets are useful for the upcoming VERITAS (Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy) and EnVision missions and would specifically benefit from the repeat pass interferometry of VERITAS, which detects surface deformation and can therefore in principle constrain the maximum displacement of surface faulting at locations that are visited twice during the mission. 

How to cite: van Zelst, I., De Toffoli, B., Garcia, R. F., Ghail, R., Gülcher, A. J. P., Horleston, A., Kawamura, T., Klaasen, S., Lefevre, M., Lognonné, P., Maia, J., Näsholm, S. P., Panning, M., Plesa, A.-C., Sabbeth, L., Smolinski, K., Solberg, C., and Stähler, S.: Seismicity on Venus: optimal detection methods and target regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12790, https://doi.org/10.5194/egusphere-egu24-12790, 2024.

Observations of Venus imply ongoing tectonic and volcanic activity, suggesting the planet is dynamically active^[1,2]. Tectonically altered regions, such as ridges or tesserae, indicate surface mobility. However, unlike Earth, no evidence of active plate tectonics has been identified. The tectonics and volcanism of terrestrial planets are closely tied to active mantle convection modes. Rheology, a crucial element in tectonics, is influenced by the presence of water^[3]. Despite this, the impact of water has largely been overlooked in Venus studies, as its interior is typically assumed to be dry. This assumption is being challenged by indications of significant hydrodynamic escape into space, requiring volcanic replenishment. Consequently, water is likely still present in Venus' interior, even if the concentrations are unknown. Importantly, the potential effects of water on Venus' dynamics and evolution remain poorly understood. The interplay between water, mantle dynamics, and volcanic activity would likely contribute to a more comprehensive understanding of Venus' evolution.  This underlines the need to consider complex dynamic thermo-magmatic models that account for water, including composition-dependent finite water solubilities.

In this study, we use the numerical code StagYY to perform state-of-the-art 2D models in a spherical annulus geometry to assess the effects of water on the tectono-magmatic evolution of Venus^[4,5]. Particular attention will be given to the way water influences mantle convection and tectonics. Indeed, results show that the presence of water can dramatically change the geodynamic regime through the rheology, melting and outgassing. With the introduction of composition-dependent water solubility maps, dehydration processes will redistribute water throughout the mantle^[6]. Since water content is directly related to the viscosity structure, the convective regime is expected to change as well. The main question we want to address is how dehydration processes and water distribution influence the convective and tectonic regimes of Venus. Studying the impact of water on Venus's interior may not only unveil insights into its tectonic evolution but also sets the stage for crucial future research, advancing our broader understanding of planetary processes and habitability.

^[1] Smrekar, S. E., Stofan, E. R., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., ... & Drossart, P. (2010). Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science, 328(5978), 605-608.

^[2]Gülcher, A. J., Gerya, T. V., Montési, L. G., & Munch, J. (2020). Corona structures driven by plume–lithosphere interactions and evidence for ongoing plume activity on Venus. Nature Geoscience, 13(8), 547-554.

^[3]Karato, S. I. (2015). Water in the evolution of the Earth and other terrestrial planets. Treatise on Geophysics, 9, 105-144.

^[4] Tackley, P. J. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors, 171(1-4), 7-18.

^[5]Tian, J., Tackley, P. J., & Lourenço, D. L. (2023). The tectonics and volcanism of Venus: New modes facilitated by realistic crustal rheology and intrusive magmatism. Icarus, 399, 115539.

^[6]Nakagawa, T. (2017). On the numerical modeling of the deep mantle water cycle in global-scale mantle dynamics: The effects of the water solubility limit of lower mantle minerals. Journal of Earth Science, 28(4), Article 4. https://doi.org/10.1007/s12583-017-0755-3

How to cite: Metternich, M., Tackley, P. J., Moccetti Bardi, N., and Lourenço, D. L.: Water and the tectonic regime of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19372, https://doi.org/10.5194/egusphere-egu24-19372, 2024.

The recent analysis of radar data from NASA’s Magellan mission suggests that volcanic activity is ongoing on Venus [1], providing unprecedented evidence that Venus’s evolution and present day state has been dominated by volcanic processes. Venus’s geodynamics and tectonics seem to be well characterized by the so-called “plutonic squishy lid” regime, where part of the melt that is formed in the interior rises to the surface but a significant part remains trapped in the crust and lithosphere forming intrusions [2]. These intrusions strongly influence the mantle’s thermal evolution, heat flow, and the present-day thermal state of the subsurface.

This study focuses on the effects of intrusive magmatism on the lithosphere thickness and thermal gradient. The latter is used to evaluate our models by comparing our results to estimates based on studies of the elastic lithosphere thickness [3,4,5]. We use the geodynamic code Gaia in a 2D spherical annulus geometry [6]. Our models vary the intrusive to extrusive ratio from a fully intrusive case to a fully extrusive one and the intrusive melt depth from 10 km to 90 km.

Our models show that depending on the percentage of extrusive melt and the depth of magmatic intrusions, the maximum thermal gradient varies from a few K/km up to almost 40 K/km at present day, with higher values obtained for higher percentages of intrusive melt and shallower the magmatic intrusions. Moreover, our results show that the thermal gradients have remained similar during the last 750 Myr. Models in which the extrusive magmatism is higher than 60% and the depth of magmatic intrusions lies deeper than 50 km cannot explain high local thermal gradients as suggested by studies of elastic lithosphere thickness [3,4,5].

In a recent study [7], the presence of a low viscosity layer (LVL) in the shallow Venusian mantle has been suggested to be related to the presence of partial melt. The LVL starts beneath the lithosphere at depths shallower than 200 km. This places constraints on the depth of melting that we can use to select successful models. Models that are compatible with partial melting starting at depth of 200 km or less beneath the surface require less than 40% extrusive magmatism and an intrusive melt depth strictly higher than 10 km.

We use our models to estimate ranges for melting conditions in the interior at present day. The range of melt temperatures lies between 2000 and 2250 K and the depth of melting between ~200 and 360 km. These estimations serve as a starting point for and will be compared with high-pressure-high-temperature laboratory experiments that will be performed at the University of Münster to select the most likely mantle compositions of Venus that can explain the Venera and Vega data.

References:

[1] Herrick & Hensley, Science, 2023. [2] Rolf et al., SSR, 2023. [3] Smrekar et al., Nature Geoscience, 2023. [4] Borelli et al., JGR, 2021. [5] Maia et al., JGR, 2022. [6] Hüttig et al., PEPI, 2013. [7] Maia et al., GRL, 2023.

How to cite: Herrera, C., Plesa, A.-C., Maia, J., Klemme, S., and Jennings, L.: Thermal evolution and magmatic history of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5946, https://doi.org/10.5194/egusphere-egu24-5946, 2024.

The spin period of Venus is anomalously large. With one Venusian day being 243 Earth days, the rotational bulge of
Venus has the amplitude of only tens of centimetres, making the Earth’s hotter twin the least rotationally stable planet in
the Solar System. Being a slow-rotator creates a unique link between internal and rotational dynamics. This is because,
on a slow-rotator, convection driven redistribution of mass may produce perturbations of the body’s inertia tensor that
are comparable in amplitude with the inertia of the rotational bulge. Venus thus may respond to mantle convection by
wobbling (Spada et al., 1996), and wobbling is detectable when both the rotational and the figure axes are measured
accurately. The present-day estimate of the angle between the two axes is 0.5°, but it is based on gravity models with a
limited resolution (Konopliv et al., 1999). Future missions to Venus, namely VERITAS and EnVision, are likely to provide
a more robust measurement.

The geodynamic regime of Venus’ mantle remains enigmatic. Observational data does not support the existence of
continuous plate tectonics on its surface, but some recent evidence of ongoing tectonic and volcanic activity (e.g. Herrick
and Hensley, 2023) and crater statistics analyses (e.g. O'Rourke et al., 2014) indicate that the planet is unlikely to be in a
stagnant lid regime (see also Rolf et al., 2022). Here we perform 3D spherical mantle convection simulations of the different
possible tectonic scenarios and compute the resulting reorientation of Venus. The reorientation is accompanied by a wobble
whose average amplitude we evaluate and compare to the present day estimate of 0.5° (Konopliv et al., 1999). Since the
different convective regimes predict vastly different rotational dynamics, the comparison provides a useful constraint on
the interior dynamics of Venus. This work was supported by the Czech Science Foundation through project No. 22-20388S.

References
Herrick, R., Hensley, S., 2023. Surface changes observed on a venusian volcano during the magellan mission. Science
doi:10.1126/science.abm7735.

Konopliv, A., Banerdt, W., Sjogren, W., 1999. Venus gravity: 180th degree and order model. Icarus 139, 3–18.
doi:10.1006/icar.1999.6086.

O'Rourke, J.G., Wolf, A.S., Ehlmann, B.L., 2014. Venus: Interpreting the spatial distribution of volcanically modified
craters. Geophys. Res. Lett. 41, 8252–8260. doi:10.1002/2014gl062121.

Rolf, T., Weller, M., Gulcher, A., Byrne, P., O’Rourke, J.G., Herrick, R., Bjonnes, E., Davaille, A., Ghail, R., Gillmann,
C., Plesa, A.C., Smrekar, S., 2022. Dynamics and evolution of venus’ mantle through time. Space Science Reviews 218,
70. doi:10.1007/s11214-022-00937-9.

Spada, G., Sabadini, R., Boschi, E., 1996. Long-term rotation and mantle dynamics of the Earth, Mars, and Venus.
J. Geophys. Res. Planets 101, 2253–2266. doi:10.1029/95JE03222.

How to cite: Patočka, V., Maia, J., and Plesa, A.-C.: The link between internal and rotational dynamics of Venus: The amplitude of mantle convection-driven wobble, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12316, https://doi.org/10.5194/egusphere-egu24-12316, 2024.

The electrical environment of Venus has been investigated through extensive considerations of whether lightning has been detected in the atmosphere [1]. Although an important process, the presence or absence of lightning does not completely describe Venus’ electrical environment. Little consideration has been made of other related aspects, such as the possible presence of a global atmospheric electric circuit, as is present on Earth. In this context, lightning would be regarded as the source in a possible global circuit, which distributes charge across a planet. New arguments for and against a global electric circuit in Venus’ atmosphere are presented here which arise from re-analysis of data from the Venera 13 & 14 landers.

On Earth, the global atmospheric electric circuit connects regions of disturbed weather to distant regions of fair weather, by current flow between the conducting ionosphere and surface. Disturbed weather regions produce the potential difference between these conducting layers, which drives the current flow. The presence of a similar global circuit on other planets has been proposed, but their existence remains an open question, which motivates further work [2].

The Venera 13 & 14 landers descended through Venus’ atmosphere carrying a wealth of instrumentation. Each lander carried a point discharge sensor, which recorded electrical discharges between the spacecraft and the atmosphere [3]. The discharges recorded were difficult to explain using existing models of Venus’ environment, so it was previously proposed that low atmosphere haze layers could have caused them [4]. Further evidence for these haze layers has been provided by spectroscopic data from the Venera landers, which showed significant atmospheric extinction in the same region [5]. We have attempted to investigate whether it would be plausible for haze layers to cause both the electrical and extinction effects, and whether this favours a global electric circuit in Venus’ atmosphere.

To investigate this, a model describing electrical interactions in Venus’ atmosphere has been produced. The effects of different haze layers on Venus’ electrical environment were able to be studied, via different inputs to the model. The haze layer properties have been constrained by the spectroscopic observations. Results from the electrical modeling were compared with the electrical discharges recorded by the landers, allowing us to determine the conditions which best recreate these observations. Our investigations show that similar results to the observed Venera data can be produced by the electrical model when the effects of a global atmospheric electric circuit are included, but not when they are neglected. These findings are not definitive, but they do provide supporting evidence for the presence of a global electric circuit in Venus’ atmosphere.

References:
[1] R.D. Lorenz (2018). Progress in Earth and Planetary Science, 5. [2] K.L. Aplin (2006). Surveys in Geophysics 27. 63-108. [3] L. Ksanfomality et al. (1982). Soviet Astronomy Letters, 8. 230–232. [4] R.D. Lorenz (2018). Icarus, 307. 146-149. [5] B. Grieger (2003). Proceedings of the International Workshop Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science. 63–70.

How to cite: McGinness, B., Harrison, G., Aplin, K., Airey, M., and Nicoll, K.: New Evidence for a Global Atmospheric Electric Circuit on Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13391, https://doi.org/10.5194/egusphere-egu24-13391, 2024.