Venus is not ife on Venus?generally at the forefront when considering extraterrestrial life. Yet, based on the physical similarities and proximity to Earth and with the little knowledge of its evolutionary history speculate, there is a possibility that Venus may have hosted life in the past on the surface if Venus had liquid water and perhaps even present in the clouds today. While the early suggestions during the beginning of the space exploration about life on Venus were mostly speculative due to limited data, recent interest has arisen from realizations (i) the unexplained ultraviolet absorption spectrum of Venus resembles many organics, (ii) there is chemical disequilibria in the cloud layer, (iii) the cloud aerosols likely contain significant abundances of hydrated iron and magnesium sulfates, and (iv) the solar radiation received in the cloud layer contains the appropriate wavelengths and flux to support phototrophy. Considering the extreme survival of many terrestrial microorganisms, the possibility remains that any extant life on Venus in the past could have adapted to survival in the cloud layer far above the surface where energy, nutrients are available but the precise compositions of the cloud particles and water availability are still uncertain. The key to solving the mystery of life on Venus is to determine if Venus had liquid water on the surface in its past and to measure the precise chemical composition of the Venus atmosphere and the cloud particles.
How to cite: Limaye, S.: Life on Venus?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11995, https://doi.org/10.5194/egusphere-egu25-11995, 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 20-50 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 50-70 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.
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, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6334, https://doi.org/10.5194/egusphere-egu25-6334, 2025.
The modern Venus atmosphere has substantially lower water vapour abundance [1-3] and a high deuterium to hydrogen ratio (D/H) compared to Earth [3,4]. The high D/H suggests a significantly larger initial water reservoir than today. Some studies suggest an initial temperate climate, with a dayside cloud-albedo feedback supporting early and prolonged surface Habitability [5,6] and ending with a runaway greenhouse effect possibly triggered by large-scale volcanism [7]. Water vapour photodissociation and preferential loss of the lighter hydrogen would explain the observed D/H [8]. Other studies claim that warming from nightside stratospheric clouds could prevent water condensation [9].
Assuming surface water condensation from a steam atmosphere in the first place, we use a 3D General Circulation model (GCM) to simulate a hypothetical ocean on Venus (2.9 Ga). 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 [10]. The simulations use a spatial resolution of 4ºx5º (latitude x longitude), a 40-layer atmosphere (top pressure: 0.1-hPa) and a 13-layer fully dynamic ocean [11] 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 results suggest the presence of deep mixed layers in the polar seas and the development of a complex meridional overturning circulation, controlled in part by the landmass configuration and bathymetry. In addition, we will explore the impact of parameters such as rotation rate, insolation, and ocean thickness on ocean circulation.
References: [1] Bézard B., et al.,2011.Icarus.216:173; [2] Cottini V., et al.,2015.Planet. Space Sci.113:219; [3] Encrenaz T., et al.,2015.Planet. 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] Way M.J., et al.,2022.Planet. Sci. J.3:92; [8] Chaffin M.S., et al.,2024.Nature.629:307; [9] Turbet M., et al.,2021.Nature.598:276; [10] Way M.J., et al.,2017.ApJS.213:12; [11] Russell G.L., et al.,1995.Atmos-Ocean.33:683.
Acknowledgements: This work was funded by the Portuguese Fundação para a Ciência e Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) –UID/50019/2025 and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and research grants UIDB/04434/2020 (https://doi.org/10.54499/UIDB/04434/2020) and UIDP/04434/2020 (https://doi.org/10.54499/UIDP/04434/2020). DQ acknowledges FCT a PhD fellowship 2023.05220.BD. JCD also acknowledges FCT a CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002 (https://doi.org/10.54499/CEECINST/00032/2018/CP1523/CT0002).
How to cite: Quirino, D., Way, M. J., Green, J. A. M., Duarte, J. C., and Machado, P.: Ocean circulation on a temperate paleo-Venus simulated with ROCKE-3D, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-730, https://doi.org/10.5194/egusphere-egu25-730, 2025.
Venus has recently garnered significant attention with the approval of three new missions: EnVision (ESA), DAVINCI+ (NASA), and VERITAS (NASA). Among the most important features of Venus, its thick clouds play a crucial role in regulating the current environment, influencing mission planning, and affecting planetary evolution and habitability. The sulfuric acid clouds are governed by the sulfur cycle, which exhibits considerable spatial and temporal variations and remains largely unknown. Furthermore, most chemical models treat the clouds as fixed boundaries to simulate the atmosphere above or below them, thereby avoiding the complexities of cloud calculations. Consequently, the sulfur-bearing species above and below the clouds are often inconsistent across these studies, particularly regarding SO2 and SO3.
Given that sulfur originates from chemical processes and that clouds feedback into the chemistry through dynamics, radiative transfer, and gas-liquid exchange, we emphasize the critical coupling effect between clouds and atmospheric chemistry in regulating the sulfur cycle on Venus. In light of this, we have undertaken a series of efforts.
Firstly, we developed a 1D H2SO4-H2O binary condensation model to trace cloud cycles and investigate the impact of cloud acidity on the condensation process. This model generates self-consistent profiles of gas and liquid abundances of relevant species, cloud mass loading, acidity, and particle size that align with observational data. We found that the significant supersaturation of H2SO4 in the upper clouds is regulated by its chemical production rate. Based on this finding, we further simplified the condensation processes and constructed a semi-analytical cloud model, which significantly reduces the computational time for Venusian cloud modeling to just 15 seconds per run, facilitating cloud coupling studies.
Additionally, we developed a 1D atmospheric chemistry-transport model for Venus that spans the middle and lower atmospheres, incorporating updated chemical processes. The derived abundances of crucial species are consistent with observations. Our results confirm that the rapid dissolution-release cycle of SO2 could lead to its significant gradient within the clouds. This study suggests that liquid SO2 in the clouds may buffer variations in sulfur-bearing species and that the sulfur cycle could influence O2 abundance. Our next step is to couple the cloud model and the photochemical model to explore the feedback of clouds on the atmosphere in greater detail.
How to cite: Dai, L., Shao, W., Zhang, X., Cui, J., and Fan, S.: 1D model studies of Venusian sulfur cycles in the clouds and atmospheric chemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2524, https://doi.org/10.5194/egusphere-egu25-2524, 2025.
The upper haze region of Venus’ atmosphere (~70-90 km) has been shown to experience cold pockets, likely induced by gravity waves. Within this region, temperatures may become sufficiently low (< 160 K) to induce homogeneous ice nucleation in sulphuric acid droplets which might lead to ice cloud formation. Here, we first explored the homogeneous nucleation of ice in sulphuric acid solutions using a liquid nitrogen-cooled cryo-microscope setup, where water-in-oil droplet emulsions (with droplets of around 10-15 µm) are created using a microfluidic device. With this setup, we were able to extend the results from previous studies to lower temperatures and higher sulphuric acid concentrations. We observed crystallisation to 170 K, but this crystallisation was increasingly restricted by very slow crystal nucleation and growth rates at lower temperatures. Crystallisation was not observed below 154 K, consistent with the formation of ultra-viscous or glassy solutions.
To further explore the possibility of ice cloud formation on Venus, we also examined the observations of temperature, water vapour mixing ratio and pressure from the Solar Occultation in the InfraRed (SOIR) instrument onboard the Venus Express orbiter. Using this data, we determined that cooling around 80 km altitude would lead to the atmosphere becoming supersaturated with respect to ice, likely causing hygroscopic growth of sulphuric acid particles. We identified two possible trajectories due to this cooling. Either the conditions result in the growth and dilution of sulphuric acid droplets until homogeneous crystallisation conditions can be met, or the trajectory will cross into the glassy region, which would stop the droplets from being able to reach equilibrium. In this scenario, the formation of glassy aerosols will either stop any nucleation occurring, or they might provide solid surfaces on which heterogeneous nucleation occurs. Either through homogeneous or heterogenous nucleation, assuming a number concentration of 0.5 cm-3, we would expect an average size of 0.6 µm ice crystals to form in the upper haze layer of Venus.
Around 36% of the SOIR profiles reveal that these altitudes occasionally experience temperature extremes which are suitably cold (< 140 K) for the deposition of crystalline CO2. A 1D model was developed to investigate the influence of gravity waves. This shows that under these conditions, crystals will grow rapidly in the cold phase of a wave to sizes large enough for precipitation downwards to the underlying warm phase where the CO2 evaporates, effectively increasing the rate of sedimentation of sulphuric acid particles. Therefore, we suggest that water ice clouds form in large parts of the upper haze layer on Venus, with CO2 ice clouds sometimes forming but rapidly precipitating and potentially redistributing sulphuric acid, water and other materials downwards.
How to cite: Thompson, K. A., Tarn, M. D., Plane, J. M. C., and Murray, B. J.: The Formation of Cirrus-Like Ice Clouds in Venus’ Upper Haze Layer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6519, https://doi.org/10.5194/egusphere-egu25-6519, 2025.
The physical origin and chemical nature of haze particles below the main sulphuric acid clouds in the Venus atmosphere is investigated. We make a number of predictions based on our theoretical models concerning the chemical state of the gas and the properties and material composition of μm-sized particles in the lower Venus atmosphere, from ground level to a height of about 50 km. Our GGchem phase-equilibrium model (Woitke et al. 2018) for the Venus surface predicts a number of metal-chloride and metal-fluoride molecules to be present in the gas over the surface in trace concentrations < 2×10−12, in particular FeCl2, NaCl, KCl and SiF4. Using an improved version of the DiffuDrift model developed by Woitke et al. (2020) we find that these molecules can deposit to form solid potassium sulphate K2SO4, sodium sulphate Na2SO4, and pyrite FeS2, at heights larger than about 15.5 km, 9.5 km and 2.4 km, respectively. We call these condensations sulphate hazes, because their opacity is insufficient to make the lower Venus atmosphere optically thick. The most prominent material is found to be Na2SO4, which is expected to deposit on the surfaces of chemically passive aerosol particles in form of a mantle with a thickness of a few 100 mono-layers. Our models predict that such haze particles, with sizes between about 0.1 to 0.3 μm, can be dredged up from the ground to reach the sulphuric acid cloud base from below by diffusion in concentrations of about 300-1500 particles per gram of gas, depending on the efficiency of coagulation. Only these sub-micron particles can reach the main cloud layer from below. Particles larger than about 2 μm are found to stay more concentrated to the ground < 10 km.
References:
Woitke, P., Helling, C., Hunter, G. H., et al. (2018), “Equilibrium chemistry down to 100 K. Impact of silicates and phyllosilicates on the carbon to oxygen ratio“, A&A 614, A1
Woitke, P., Helling, C., & Gunn, O. (2020), “Dust in brown dwarfs and extra-solar planets. VII. Cloud formation in diffusive atmospheres“, A&A, 634, A23
Rimmer P., Jordan S., Constantinou T., Woitke P., Shorttle O., Hobbs R., Paschodimas A. (2021), “Hydroxide Salts in the Clouds of Venus: Their Effect on the Sulfur Cycle and Cloud Droplet pH”, PSJ 2, 4, id133.
How to cite: Woitke, P., Helling, C., Rimmer, P., Scherf, M., Lammer, H., and Ferus, M.: Prediction of sulphate hazes in the lower Venus atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16034, https://doi.org/10.5194/egusphere-egu25-16034, 2025.
About 30 tonnes of cosmic dust particles – mostly from Jupiter Family Comets - enters Venus’ atmosphere every (Earth) day, of which around 40% ablates. This causes the injection of various metals (Fe, Mg, Si and Na in particular) into the atmosphere between 105 and 125 km. By analogy with the Earth, these metals should provide important tracers of both chemistry and atmospheric dynamics. In order to guide future observations of these metals, both from terrestrial telescopes and spacecraft, we have developed detailed chemical networks for each of the elements. These networks are extensions of those used to model these metals in the terrestrial atmosphere, where the Fe, Mg and Na networks have been rigorously tested against observations of neutral and ionized metal atoms made with ground-based lidars, spaceborne spectrometers, and sub-orbital rockets. For Venus, we now include a detailed chlorine chemistry because of the very large concentration of HCl produced by volcanic emissions. Where reactions have not been studied in the laboratory, we have employed quantum chemistry calculations combined with master equation rate theory for reactions taking place on multi-well potential energy surfaces. These networks were then inserted into the global Venus Planetary Climate Model. The simulations reveal that the metal atoms occur in layers about 10 km wide which peak around 110 km, and the metal ion layers peak about 10 km higher. Below 105 km the metals form carbonates, which are then converted into chlorides by reaction with HCl emitted by surface volcanoes. In this presentation we will discuss the metal layer variability on the day- and night-side, and the feasibility of detecting Mg, Mg+ and Na by observing solar-pumped resonance fluorescence on the dayside, and Na chemiluminescence on the night-side.
How to cite: Plane, J., Egan, J., Feng, W., Lefèvre, F., Lebonnois, S., and Stolzenbach, A.: Meteoric Metal Layers in the Upper Atmosphere of Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4502, https://doi.org/10.5194/egusphere-egu25-4502, 2025.
We have demonstrated that the combination of matrix isolation infrared (MI-IR) spectroscopy and vibration configuration interaction (VCI) calculations [1-3] is a feasible approach [4] to accurately assign and interpret IR spectra of single molecules, such as water [5], fluoroethane [6], carbon dioxide and methane [7].
Relying on our integral experimental-computational methodology for IR spectroscopy, we investigated carbon dioxide dimerization [8], including MI-IR spectroscopy of carbon dioxide monomers CO2 and dimers (CO2)2 trapped in neon and air. Based on our VCI calculations accounting for mode-coupling and anharmonicity, we identify additional IR-active bands in the MI-IR spectra due to the (CO2)2 dimer. In a systematic carbon dioxide mixing ratio study using neon matrices, we observe a significant fraction of the dimer at mixing ratios above 300 ppm, with a steep increase up to 1000 ppm. In neon matrix, the dimer increases the IR absorbance by about 15% at 400 ppm compared to the monomer absorbance alone. This suggests a high fraction of the (CO2)2 dimer in our matrix experiments.
In atmospheric conditions, such increased absorbance would significantly amplify radiative forcings and, thus, greenhouse warming. In the context of planetary atmospheres, our results improve our understanding of the greenhouse effect for planets of relatively thick CO2 atmospheres, such as Venus, where a significant fraction of the (CO2)2 dimer can be expected. There, the necessity of including the mid-IR absorption by stable (CO2)2 dimers in databases used for modeling radiative forcing, such as HITRAN, arises.
References
[1] G. Rauhut, JCP, 121, 19 (2004)
[2] M. Neff et al, JCP, 131, 12 (2009)
[3] H. J. Werner et al, JCP, 152, 14, (2020)
[4] D. F. Dinu et al, TCA, 139, 12, (2020)
[5] D. F. Dinu et al, JPCA, 123, 38 (2019)
[6] D. F. Dinu et al, JMS, 367, (2019)
[7] D. F. Dinu et al, PCCP, 22, 32 (2020)
[8] D. F. Dinu et al, JPCA, 126, 19, (2022)
How to cite: Dinu, D. F., Bartl, P., Quoika, P. K., Podewitz, M., Liedl, K. R., Grothe, H., and Loerting, T.: Increase of radiative forcing through mid-IR absorption by stable CO2 dimers? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15992, https://doi.org/10.5194/egusphere-egu25-15992, 2025.
Polarimetry is a powerful tool to characterise a planet's clouds and hazes. The degree of polarisation of sunlight that is reflected by a planet is very sensitive to the illumination and viewing angles, the wavelength of the light, and the composition, size, and shape of the cloud and haze particles. Additionally, the degree of polarisation is rather insensitive to instrumental errors and to uncertainties in the total flux of sunlight reaching the planet.
EnVision, ESA’s next Venus orbiter, will carry the spectrometers VenSpec-U and VenSpec-H, both of which are polarisation-sensitive. Accurate measurements of the total (polarised + unpolarised) flux of the sunlight that Venus reflects therefore require information about the degree of polarisation of the incoming light. VenSpec-H includes polarisation filters that, apart from correcting for the polarisation sensitivity, will also provide valuable science data.
To support the total flux and polarisation measurements, we have developed a state-of-the-art Fortran radiative transfer code based on the Monte Carlo technique. This code enables us to simulate VenSpec-U and -H observations, fully accounting for the polarisation of light. With our model simulations, we can investigate how the measurements should be taken to minimise the errors and to maximise the amount of atmospheric information that can be retrieved. The code also accounts for the sphericity of Venus’ atmosphere, which is important for accurate simulations in twilight and polar regions. In this talk, we will show simulations of the total flux and polarisation signals of the sunlight that is reflected by Venus and discuss the spectropolarimetric signatures of the clouds and hazes.
How to cite: Trees, V., Stam, D., Yzer, M., Wang, P., and Siebesma, P.: Modelling Venus's Spectropolarimetric Signatures for EnVision, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17483, https://doi.org/10.5194/egusphere-egu25-17483, 2025.
EnVision is the fifth Medium-class mission in ESA’s Science Program, selected in June 2021 and adopted in January 2024. EnVision is an ESA-led mission in partnership with NASA, where NASA provides the Synthetic Aperture Radar payload and mission support. The mission launch is scheduled for 2031; science operations at Venus will start early 2035 following the mission cruise and aerobraking phase to achieve a low polar orbit. The scientific objective of EnVision is to provide a holistic view of the planet from its inner core to its upper atmosphere, studying the planet's long-term history, activity and climate. EnVision aims to establish the nature and current state of Venus’ geological evolution and its relationship with the atmosphere. EnVision’s science objectives are to: (i) characterize the sequence of events that formed Venus' surface, and the geodynamic framework that has controlled Venus' internal heat release ; (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 its surface.
The nominal science phase of the mission will last six Venus sidereal days (~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 VenSAR S-band radar will perform targeted surface imaging, polarimetric and stereo imaging, radiometry, and altimetry. The high-frequency Subsurface Radar Sounder (SRS) will sound the upper crust in search of material boundaries. Three spectrometers, VenSpec-U, VenSpec-H, and VenSpec-M, operating in the UV and Near- and Short Wave-IR, 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. All instruments have substantial heritage and robust margins relative to the requirements, with designs suitable for operation in the Venus environment. The EnVision science teams will adopt an open data policy, with public data release of the scientific data after validation and verification. Public calibrated data availability is <6 months after data downlink.
How to cite: Widemann, T., Straume Lidner, A. G., Schulte, M., and Pacros, A.: Science objective and status of the EnVision Mission to Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21105, https://doi.org/10.5194/egusphere-egu25-21105, 2025.
Some of the most outstanding questions about the evolution and present-day state of Venus involve the current level of volcanic activity and its surface composition, both directly linked to the amount of differentiation that our neighbor experienced through time. Several observations indicate that Venus was volcanically active in the recent past and that magmatic activity may still be ongoing [e.g., 1,2,3,4,5].
While there is growing evidence that Venus is a geologically active world, information about the surface composition and the level of magmatic activity is still needed. Three Venus missions (ESA’s EnVision and NASA’s VERITAS and DAVINCI missions) are scheduled to launch at the beginning of the next decade and explore our sister planet with unprecedented detail. All three missions include instruments targeting the 1 µm spectral region [6] where Fe transitions occur that may distinguish differences in surface composition [7]. Here we focus on the Venus Emissivity Mapper instrument, which is called VenSpec-M on EnVision mission and VEM on VERITAS mission, which will be used as a multi-spectral imaging systems [8, 9]. On EnVision, VenSpec-M is part of the VenSpec Suite, and together with high-resolution IR (VenSpec-H) and UV (VenSpec-U) spectrometers, it will provide critical information for understanding the surface-atmosphere interactions on Venus.
Both VenSpec-M and VEM instruments have six surface bands that cover five atmospheric windows around 1 µm. These will be used to distinguish between different rock types using relative (via slope and ratios between bands) and absolute (by comparison with laboratory experiments) emissivity. The instruments will also search for active volcanic eruptions on Venus using surface bands to search for thermal signatures associated with active volcanism, and three additional water vapor bands that are sensitive to the abundance of water vapor potentially associated with volcanic outgassing.
Currently, measurements are performed at PSL with the goal of building a comprehensive dataset for the interpretation of VEM data. These include measurements on basalts vs. granites samples; investigations of end-member mineral mixing effects in emissivity [10]; and studies of the emissivity response of weathered vs. unweathered Venus analogs [11]. Measurements on samples collected during field campaigns can be compared to field measurements performed using a VEM instrument emulator to improve data interpretation and calibration techniques [12]. The surface mapping performed by VenSpec-M on EnVision combined with VEM on VERITAS will characterize emissivity changes and provide nearly full coverage of Venus surface.
Acknowledgements: A portion of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract 80NM0020F0035 with NASA.
References:
[1] Helbert et al., GRL, 2008. [2] Smrekar et al., Science, 2010. [3] Smrekar et al., Nat. Geosci., 2023. [4] Herrick & Hensley, Science, 2023. [5] Sulcanese et al., Nat. Astron., 2024. [6] Helbert et al., Bulletin of the AAS, 2021. [7] Mueller et al., JGR, 2008. [8] Helbert et al. Proc. SPIE 10765, 2018. [9] Helbert et al., Proc. SPIE 11128, 2019. [10] Alemanno et al., LPSC, 2024. [11] Alemanno et al., LPSC, 2025. [12] Garland et al., LPSC, 2025.
How to cite: Plesa, A.-C., Alemanno, G., Mueller, N., Helbert, J., Dyar, M. D., Robert, S., Marcq, E., Widemann, T., and Smrekar, S. E.: Constraining surface composition and searching for volcanic activity on Venus: Preparing for future emissivity measurements by EnVision's VenSpec-M and VERITAS's VEM instruments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12314, https://doi.org/10.5194/egusphere-egu25-12314, 2025.
The interior of Venus remains a mystery and, it is challenging to reconcile the available meager observations. The leading theory for the absence of a Venusian magnetic field is that heat within Venus remains trapped beneath the stagnant lid, raising the mantle temperature and limiting flow through the core-mantle boundary. While there are only three surface compositions from the Venera and Vega landers, they are consistent with Mid-Ocean Ridge Basalts (MORB) or Ocean Island Basalts (OIB) implying that in the melting region the mantle of Venus is nothotter than the mantle of Earth. This is a surprising result because stagnant (or squishy) lid planets have hotter interiors than mobile lid planets implying that Venus has not been in the stagnant (or squishy) lid mode of convection for much of its evolution or, another heat transport mechanism—such as heat piping—has played a critical role in the flux of heat through the lithosphere of Venus. We see little change in the geoid or topography power spectra between the calculations suggesting that the presence or absence of lithospheric mobility has only a modest impact on the large-scale geoid or topography. While the patterns of the geoid or topography are not likely to be matched by any convection calculation, the power spectrum is independent of coordinate system and thus, a more robust comparison between calculation and planet. The cases we have found predict a significant heat flux from the core to the mantle—as long as 1000 Myr after an overturn event—inconsistent with the absence of a present-day magnetic field and the estimated age of the surface from cratering, the next step will be to consider a Basal Magma Ocean (BMO) to sequester heat within the core.
How to cite: King, S., Maas, C., and Stein, C.: Venus surface compositions suggest upper mantle temperatures like Earth, so why is there no magnetic field?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6540, https://doi.org/10.5194/egusphere-egu25-6540, 2025.
Models of Venus's interior structure were developed based on PREM. These models are derived by solving the differential equations for mass and hydrostatic equilibrium throughout the planet and are fully characterized by the core radius Rc and two parameters denoted as A and B. The pressure dependence of the density in Venus’ mantle ρ(P) is modeled by scaling PREM’s ρ(P) with a factor A. Differences in density between these planets can arise from differences in composition and temperature. For instance, models with A<1 may correspond to a mantle with higher temperatures and/or lower iron content compared to Earth's mantle. Similarly, the density in Venus’ liquid core is obtained by scaling PREM’s ρ(P) with a factor B. We investigate Rc values ranging from 3000 to 3500 km and B values from 0.98 to 1.02. For each combination of Rc and B, we calculate the exact value of A required for our Venus model to satisfy the mass constraint. The A values range from as low as 0.92 when the core is large and dense, to as high as 1.04, associated with a smaller, less dense core. Shear and bulk moduli profiles were also obtained based on PREM.
In all models the pressure at the very center of the planet is considerably lower than the pressure at Earth’s ICB. This suggests that Venus could only have a solid inner core if the composition and temperature values in its core differ substantially from Earth’s.
Margot et al. (2021) estimated Venus's moment of inertia (MoI) to be 0.337 ± 0.024. The MoI values of all our models fall within this range, with Rc values between 3050 km and 3225 km yielding the closest match to 0.337. However, the uncertainty in this MoI estimate is too large, necessitating the use of additional constraints to study Venus's interior structure.
Venus’ tidal Love number k2 was estimated to be 0.295 +- 0.033 in Konopliv and Yoder (1996). In order to compute the Love numbers of our Venus models, we have developed a series of realistic viscosity profiles based on estimates available in literature. The anelasticity of Venus’ interior is modeled with an Andrade rheology, which depends on two parameters (α and ζ). In Amorim and Gudkova (2025) estimates of these parameters were obtained for Earth’s mantle, and similar but wider ranges are applied to Venus in this work.
The Love numbers of each of Venus's interior structure models were calculated using different viscosity profiles and Andrade parameter values. A statistical analysis of all models was conducted based on the available estimates of Venus's MoI and k2. The core radius is most likely within the range of 3125 km to 3400 km. For low-viscosity models, Rc is expected to be closer to 3125 km, while for high-viscosity models, it must be closer to 3400 km.
The tidal phase lag and the h2 Love number were also computed for all our models as a prospective for future missions to Venus that might measure them.
How to cite: Oliveira Amorim, D. and Gudkova, T.: Constraining the interior structure of Venus based on its moment of inertia and k2 values, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10767, https://doi.org/10.5194/egusphere-egu25-10767, 2025.
Venus' mass and radius are similar to those of Earth. However, Venus' interior structure and chemical composition are poorly constrained. Seemingly small deviations from the Earth might have important impacts in the long-term evolution and dynamics of Venus when compared to our planet and could help to explain the different present-day surface and atmospheric conditions and geophysical activity between these two planets. Shah et al. (ApJ, 2022) presented a range of possible bulk compositions and internal structures for Venus. Their models, designed to fit Venus' moment of inertia and total mass, predict core radii ranging from 2930-4350 km and include substantial variations in mantle and core composition. In this study, we pick ten different Venus models from Shah et al. (ApJ, 2022) that range from a small to a big, and from a S-free to a S-rich core. We run mantle convection evolution models for the different scenarios using the code StagYY (Tackley, PEPI 2008; Armann et al., JGR 2012) and explore how different interior structures and chemical compositions affect the long-term evolution and dynamics of Venus. In our models, the bulk composition of the mantle affects the basalt fraction and the solidus and liquidus temperature profiles. We investigate how the composition and size of the core affects magmatism hence outgassing of water and other volatiles to the atmosphere, the basalt distribution, heat flow, temperature of the mantle and lithosphere, and observables such as the moment of inertia and Love numbers. Since the tectonic regime active on Venus is still unknown, we test different evolution scenarios for a planet covered by a stagnant lid, an episodic lid, and a plutonic-squishy lid. The models produce a range of predictions that can be compared to observations by planned missions to Venus, including EnVision measurements by the VenSpec spectrometers, comprising outgassing of water and other volatiles and surface composition. These can be used to constrain Venus' interior composition and structure, and reveal key information on the differences between Earth and Venus.
How to cite: Lourenço, D., Tackley, P., Patočka, V., Rolf, T., Grünenfelder, M., Shah, O., and Helled, R.: Influence of Possible Bulk Compositions on the Long-Term Evolution and Outgassing of Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12144, https://doi.org/10.5194/egusphere-egu25-12144, 2025.
Understanding the interior of our sister planet ahead of the next generation of Venus missions has become more imperative as its current and past state has remained an enigma. Venus does not currently have a mobile lid like Earth, yet it has a more tectonically active surface than any other stagnant-lid body in our solar system. Rifting is particularly an important process to study because rifts are a crucial feature of a mobile-lid planet. Rifts on Venus are spatially correlated with coronae, indicating that rifts are influenced by mantle dynamics and magmatism. The tectonic deformation associated with rifting, the emplacement of plutons, and the viscous relaxation of the lower crust are all informed by gravity-derived crustal thickness.
The gravity field from the Magellan mission has heterogenous resolution with a degree strength as low as spherical harmonic 40 (spatial block size of 475 km), which is coarser than the scale of Venus’s rift zones, Nevertheless, we can study rifting on Venus by focusing on a number of rift zones in regions with a degree strength of 95 (spatial block size of ~200 km).. This study area includes a majority of the BAT region as well as many major rift zones, and we find systematic trends of crustal thickening in addition to crustal thinning . The higher-resolution gravity fields recovered by VERITAS and EnVision will allow us to resolve all rift zones on Venus to fully understand the role of rifting on Venus and how it may shape/shaped Venus’ surface.
How to cite: Mills, A. and James, P.: Nature of Rifting on Venus Revealed by Gravity-Derived Crustal Thickness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-763, https://doi.org/10.5194/egusphere-egu25-763, 2025.
Venus is, in terms of size, density and composition, the most similar planet to Earth. Still, the two planets differ greatly in their surface conditions, tectonic regime and volcanic signatures. Solving the enigma of how and why they evolved to be so different is of particular importance in order to understand habitability in the universe. This study investigates how Venus’ high surface temperature, one of its key features, influenced the interior evolution of the planet. Our work aims to explain the tectonic regime, its surface expressions on Venus, and the importance of the surface temperature in planetary evolution. Furthermore, it strives to forecast the temperature dependence of the tectonic regime for a Venus-like planet. Our results could be used to refine our understanding of conditions necessary for planetary habitability and the influence of the surface temperature on volcanism and outgassing. Insights gained from understanding Venus’ dynamics will deepen our understanding of rocky exoplanets, from Earth-like to those located near the inner edge of the habitable zone, where surface temperatures approach Venus-like extremes.
The numerical convection code StagYY (Tackley, PEPI 2008) is used to model the 2-D thermochemical evolution and convection of a Venus-like planet. In contrast to previous studies (Gillman et al., JGR Planets 2014, Noack et al., Icarus 2012), this study includes composite rheology (dislocation creep, diffusion creep and plastic yielding), a more realistic experiment-based plagioclase crustal rheology, as well as intrusive magmatism, following Tian et al. (Icarus, 2023). The surface temperature is varied in six sets of models from 300K to 740K and the effects of these temperature variations on the interior dynamics and tectonic regime is examined. Furthermore, different rheologies are also tested, varying between a “weak” plagioclase and an olivine rheology for the crust. Finally, we tested a range of reference viscosities for the models, which control the convection vigour.
Preliminary results verify the expectations that models with higher surface temperatures produce thinner crusts susceptible to downwelling-like processes, whereas models with a lower surface temperature produce thicker, more rigid crusts. Furthermore, first results indicate that the mobility of the crust trends with surface temperature depending on the crustal rheology. As expected, models with an olivine crustal rheology have higher mobilities for higher surface temperatures, likely caused by the lithospheric weakening at higher surface temperatures. However, models that include a plagioclase rheology, show a more complex, sometimes inverse trend for their mobility, which is not displayed in their crustal thickness trends. Finally, the tectonic regime seems to be strongly dependent on the combination of temperature and rheology and our Venus-like models experience a combination of plutonic-squishy lid (Lourenço et al., G3 2020) and episodic-lid regime depending on the specific parameters of the simulation.
How to cite: Murzakhmetov, L., Gillmann, C., Lourenco, D. L., and Tackley, P.: The effects of surface temperature on the tectonic regime and interior dynamics of Venus and exoVenuses. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19808, https://doi.org/10.5194/egusphere-egu25-19808, 2025.
The Venus—Earth dichotomy inspires our understanding of the inner edge of the liquid-water Habitable Zone (HZ), yet, multiple theories exist to define the HZ inner edge and Venus's own climate history is debated. Theories of the HZ inner edge can be tested provided we can observationally distinguish Earth-like planets with liquid water oceans, from Venus-like planets with dry planetary surfaces. Dry planetary surfaces can potentially be identified by observing atmospheric sulfur dioxide (SO2), which is otherwise scrubbed from the atmospheres of Earth-like planets via wet deposition. However, SO2 in the atmospheres of Venus-like planets can be efficiently destroyed by photochemistry. We here demonstrate how the photochemical behaviour of SO2 can allow us to observationally identify dry planetary surfaces, but uniquely around M-dwarf stars. We propose a statistical comparative planetology study that can constrain the location of the inner edge of the habitable zone around M-dwarf stars in the near future using exo-Venuses rather than exo-Earths.
How to cite: Jordan, S. and Shorttle, O.: Tracing the inner edge of the Habitable Zone with exo-Venuses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13299, https://doi.org/10.5194/egusphere-egu25-13299, 2025.
The prime focus of astrobiology research is the search for life elsewhere in the universe, and this proceeds with the pragmatic methodology of looking for water and Earth-like conditions. In our solar system, Venus is the most Earth-like planet, yet at some point in planetary history there was a bifurcation between the two: Earth has been continually habitable since the end-Hadean, whereas Venus became uninhabitable. Indeed, Venus is the type-planet for a world that has transitioned from habitable and Earth-like conditions through the inner edge of the Habitable Zone (HZ); thus it provides a natural laboratory to study the evolution of habitability. A parallel approach to studying the intrinsic properties of Venus and its evolutionary history is a statistical analysis of the vast (and still rapidly growing) inventory of terrestrial exoplanets. Characterizing the atmosphere of numerous terrestrial planets and will provide critical insight into the prevalence of Venus analogs and the possible diversity of their atmospheric chemistry. In this presentation, I will describe how the current limitations in our knowledge of Venus are impacting present and future exoplanetary science, including remote sensing techniques that are being or will be employed in the search for and characterization of exoplanets. I will discuss Venus in the context of defining the boundaries of habitability, and how exoplanets are enabling tests of potential runaway greenhouse regimes where Venus analogs may reside. I will discuss specific outstanding questions regarding the Venus environment and the relevance of those issues to understanding the atmospheres and interior structure of exoplanets.
How to cite: Kane, S.: Venus in the Context of Exoplanet Demographics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3857, https://doi.org/10.5194/egusphere-egu25-3857, 2025.
The European Space Agency's EnVision mission, slated for launch in the next decade, will provide unprecedented insights into the geological and atmospheric dynamics of Venus. EnVision's primary objectives include high-resolution subsurface mapping with the Subsurface Radar Sounder (SRS), operating with 9 MHz as the central frequency. This study investigates the potential of SRS to detect electromagnetic waves generated by lightning in the Venusian atmosphere, a phenomenon whose existence remains debated.
While optical observations of lightning are hampered by Venus's dense cloud cover, previous missions like the Pioneer Venus Orbiter and the Venus Express have detected whistler mode waves, which may be indicative of lightning activity.
This research employs the Stanford Full-Wave Method to model the propagation of lightning-induced waves in the SRS frequency range. This procedure allows us to establish if a radio signal generated at the cloud level at about 50 km altitude could propagate in the ionosphere and reach the radar with detectable power. The model has been previously applied to signals with frequencies up to 100 Hz in the Venusian atmosphere. Now, it is being adapted for the propagation of radio waves up to the MHz frequency band. By simulating various scenarios involving different ionospheric conditions - including the presence of ionospheric “holes” - magnetic field strengths and discharge intensities and rates, we assess the detectability of these signals by the SRS. Our findings confirm the sensitivity of wave propagation to variations in the Venusian ionosphere's electron and ion density profiles, identifying critical magnetic field thresholds required for successful detection.
The model is also being extended to lightning phenomena on Earth to study their detectability from space in the MHz frequency range under known background conditions.
This study contributes to our understanding of Venus's atmospheric processes and provides valuable context for interpreting potential lightning signatures in EnVision's SRS data.
How to cite: Rubinetti, S., Arnone, E., Pérez-Invernón, F. J., Lehtinen, N. G., Gordillo-Vázquez, F. J., Piergotti, A., Petracca, M., Prestileo, F., Tiberia, A., Bruzzone, L., and Dietrich, S.: Assessing the potential of EnVision's Subsurface Radar Sounder for detecting Venusian lightning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-905, https://doi.org/10.5194/egusphere-egu25-905, 2025.
Surface rocks on Venus are exposed to a dense atmosphere, primarily composed of CO₂ (96.5%) and N₂ (3.5%), with trace amounts of H₂O and sulfur compounds like SO₂ and H₂SO₄, surface temperatures around 460°C and pressures ⁓ 90 times that of Earth. Understanding surface-atmosphere interactions is essential for interpreting data from NASA VERITAS and DAVINCI and ESA EnVision mission. Collaborative research between the Planetary Spectroscopy Laboratory (PSL) at DLR and the Hot Environments Laboratory (HEL) at NASA GSFC compares the emissivity responses of altered and unaltered Venus surface analogs within the 1 μm spectral region. This spectral range is significant as it corresponds to atmospheric windows in Venus' thick cloud cover, enabling remote sensing of the surface. Instruments like the Venus Emissivity Mapper (VEM) on VERITAS, VenSpec-M on EnVision, and the DAVINCI VISOR camera observe Venus in this region, requiring emissivity measurements under Venus-like conditions [1–4].
Methodology and Samples: This study selected well-characterized basalt and granite samples as Venus analogs. Here we focus on Saddleback basalt sanples from the Mojave Desert [5] prepared as slabs and granular materials of various sizes. Laboratory analyses included:
- Hemispherical reflectance measurements at ambient temperature in the near-infrared spectral range.
- High-temperature emissivity measurements under Venus-like conditions (400–480°C).
- Weathering experiments exposing samples to a simulated Venusian atmosphere in the Small Venus Chamber (Lil’ VICI) at HEL.
- Chemical analyses using micro X-ray fluorescence (µXRF) and scanning electron microscopy (SEM) for unaltered, heated, and altered samples at the Museum für Naturkunde (MfN, Berlin).
Fine granular samples, used to maximize interaction with atmospheric gases, are unlikely on Venus due to the absence of water-driven processes required for their formation [6,7]. Emissivity measurements captured NIR emissivity changes due to heating and alteration after weathering in Lil’ VICI [8]. Hemispherical reflectance measurements served as references for calibrating emissivity data.
Findings and Implications: Altered basalt samples displayed increased emissivity in the NIR range, partly due to “soot” from chemical reactions between chamber walls and SO₂ gas [9] and possibly darkening from mineral and glass breakdown at high temperatures. Comparisons between slab and granular morphologies highlighted the importance of studying various sample types to understand weathering effects comprehensively.
Future experiments will involve basaltic and granitic samples subjected to extended weathering durations and varied conditions, including comparative analyses between HEL and Glenn Extreme Environments Rig (GEER) experiments.These efforts aim to refine the understanding of weathering effects and improve data interpretation from Venus missions.
Acknowledgements: A portion of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract 80NM0020F0035 with NASA.
References:
[1] Allen D. A. et al., (1984) Nature, 307, 222–224.
[2] Pollack J. B. et al. (1993) Icarus, 103, 1–42.
[3] Plesa A.-C. et al. (2024) this meeting.
[4] Garvin J. et al. (2024) LPSC, LV, Abstract #2429.
[5] Peters et al. (2008) Icarus, 197, 470–479.
[6] Golombek, M.P. et al. (2020), LPSC LI, Abstract #2744.
[7] Dyar, M.D. et al. (2021) Icarus, 358, 114139.
[8] Alemanno G. et al. (2023) SPIE, 12686, doi: 10.1117/12.2678683.
[9] Gilmore, M.S., and Santos, A.R. (2024) LPSC LV, Abstract #2519.
How to cite: Alemanno, G., Kohler, E., Van den Neucker, A., Helbert, J., Plesa, A.-C., Maturilli, A., Dyar, M. D., Adeli, S., Barraud, O., Hamann, C., Kaufmann, F. E. D., Smrekar, S., Widemann, T., Robert, S., and Marcq, E.: Exploring Emissivity Variations of Venus Analogs Under Simulated Surface Conditions: Insights for VEM and VenSpec-M data Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4465, https://doi.org/10.5194/egusphere-egu25-4465, 2025.
Better knowledge of Venus's interior structure is crucial to understanding its history and bringing insight into why its evolutionary path diverged so significantly from Earth's. Both NASA's VERITAS and ESA's EnVision missions will conduct geophysical investigations[1] of Venus. Their radar and gravity experiments will determine the planet’s orientation, requiring a comprehensive rotation model in order to link these observations to interior and atmospheric properties.
Polar motion refers to the motion of a planet's spin axis relative to its surface. It is distinct from precession-nutation, which describes the motion of the spin axis relative to the fixed celestial sphere. Both motions provide complementary constraints for interior models.
In this study, to support the potential detection of polar motion by future Venus orbiters, we developed a polar motion model for a triaxial planet accounting for solar torque, centrifugal and tidal deformations of a viscoelastic mantle, and atmospheric dynamics. Core-mantle coupling effects were analyzed separately considering a simplified spherical core. We revisited the expression for the period of free motion known as the Chandler wobble. Solar torque is the dominant phenomenon affecting Venus's Chandler period, accelerating the wobble by a factor of 2.75, while solid deformations slow it down by less than 1.5%. We predict a Chandler period in the range [15 400; 19 400] years (core not fully crystallized) or [17 900; 20 700] years (core fully crystallized). During EnVision's four-year primary mission, the Chandler wobble manifests as a linear drift of about 75 meters of the spin pole on Venus's surface, near the resolution limit of EnVision’s VenSAR. We also computed the forced polar motion using the Venus Planetary Climate Model[2]. The forced oscillations have an amplitude of approximately 20 meters, driven roughly equally by atmospheric dynamics and solar torque.
These results suggest that Venus's Chandler wobble may be detectable by future orbiters. Venus’s precession period has already been measured with a 7% relative uncertainty[3], but is expected to be better determined by EnVision[4] and VERITAS[5]. A combined measurement of both the precession and Chandler periods will reveal the physical state of the core. If the core is not fully crystallized, the Chandler period would serve as a proxy for the mantle’s moment of inertia, providing complementary constraints for the size of the core and for thermo-chemical properties of Venus’s interior. Therefore, the wobble should be incorporated into rotation models when anticipating these missions.
[1] Widemann et al. (2023), Space Science Reviews, doi:10.1007/s11214-023-00992-w
[2] Lai et al. (2024), JGR Planets, doi:10.1029/2023je008253
[3] Margot et al. (2021), Nature Astronomy, doi:10.1038/s41550-021-01339-7
[4] Rosenblatt et al. (2021), Remote Sensing, doi:10.3390/rs13091624
[5] Cascioli et al. (2021), Planetary Science Journal, doi:10.3847/psj/ac26c0
How to cite: Phan, P.-L. and Rambaux, N.: Modeling Venus's polar motion: preparing for EnVision measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9001, https://doi.org/10.5194/egusphere-egu25-9001, 2025.
The surface of Venus is characterized by a large number of volcanic features, indicating that volcanic activity played an important role in the planet’s thermal and tectonic evolution. This volcanic activity is driven by a superheated interior and is likely to be related to either plumes coming from the deep interior or extension of the surface. The largest volcanoes have a diameter of more than 500 km, a height exceeding 3 km, and are associated with significant gravity anomalies. In order to better understand the formation of the large volcanoes on Venus and their gravity signatures, we investigate the rise and subsequent relaxation of a large-scale volcanic edifice by performing a series of 2D and 3D numerical simulations of the heat and mass transfer in Venus’ upper mantle. The numerical modeling is conducted with the finite-element code ASPECT (https://aspect.geodynamics.org/) which has been modified to include different types of fractional melting parameterization and driving mechanisms (extension, plumes of different widths and temperature, etc.). The topography and the gravity signal are computed assuming that the lithosphere behaves as a Maxwell viscoelastic solid and the results are compared with the topography and gravity around selected prominent volcanic features.
How to cite: Dizov, A., Maierová, P., and Čadek, O.: Modeling the formation of large-scale volcanoes on Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9757, https://doi.org/10.5194/egusphere-egu25-9757, 2025.
Earth’s size and composition make it comparable to Venus but these planets exhibit contrasting surface expressions due to their different tectonic regimes and surface recycling processes. Earth’s efficient recycling of its surface and the operation of plate tectonics are facilitated by the formation of extensive global subduction networks. During the Wilson Cycle, these networks drive periods of supercontinental breakup and active plate tectonics. We hypothesize that the formation of global subduction networks on Earth is promoted by the presence of water-rich continental sediments that reduce lithospheric friction at convergent margins. This is critical for inducing large-scale motion and reorganization of lithospheric plates, a key defining feature of modern plate tectonics. To explore this hypothesis, we developed a series of 3D global geodynamic models using the ASPECT code. These models reproduce 2 scenarios: (i) self-consistent plume-induced regional subduction and its reorganization into global subduction networks, (ii) prescribed inherited plate boundaries at 1Ga, demonstrating that sustained subduction activity is possible thanks to local frictional strength reduction. On Earth, such frictional reductions may fluctuate over time, driven by climatic events like Snowball Earth, which increase sediment flux and lubricate convergent plate boundaries. We compare these results with the results of models for Venus, where there is no liquid water at the surface, which implies higher frictional strength. We infer that without localized reduction of friction, regional subduction-like deformation on Venus’s dry surface is short-lived, failing to establish global subduction networks. However, in long-term, Venus can still experience episodic resurfacing as its lithosphere becomes unstable and collapses into the asthenosphere. Comparison of Earth’s and Venus’s tectonic styles highlights the role of surface water and water-rich sediments in sustaining large-scale and long-term subduction and in the development of a global network of subduction zones and plate boundaries, which is a characteristic of modern plate tectonics.
How to cite: Pons, M., Sobolev, S., and Jain, C.: Subduction network connectivity, a comparison between Earth and Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10159, https://doi.org/10.5194/egusphere-egu25-10159, 2025.
Despite their similar size and mass, Earth and Venus have very different internal dynamics that reflect contrasting modes of heat loss. On Earth, plate tectonics drive heat loss through lithosphere recycling, with a substantial contribution from hydrothermal circulation through oceanic plates, and a minor contribution from mantle plume (i.e. hot spot) activity. In comparison, the surface of Venus is more homogeneous, has lower relief, and shows abundant evidence of effusive volcanism, and its global dynamics is not well understood. Here, we present the first global heat flow map for Venus, as well as estimates of the total heat loss, obtained from an inversion of geophysical data, including lithospheric effective elastic thickness, crustal thickness, and radioactive heat production. The obtained heat flow is lower and less geographically structured for Venus than for Earth, but with maximum values reaching those typical of magmatically active terrestrial areas. Some previous works obtained widespread heat flow similar to those of active terrestrial regions were affected by the use of excessively high values for the thermal conductivity of lithospheric rocks. The obtained total heat loss is 11-15 TW, similar to estimates of the total radioactive heat production of the planet. Therefore, at present, Venus proportionally dissipates much less heat than Earth.
How to cite: Ruiz, J., Jiménez-Díaz, A., Egea-González, I., Romeo, I., Kirby, J., and Audet, P.: The heat flow of Venus from global lithosphere strength, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12084, https://doi.org/10.5194/egusphere-egu25-12084, 2025.
Despite sharing a broadly similar interior structure and composition with Earth, Venus exhibits a starkly contrasting geodynamic regime. On Venus, the coronae, large quasi-circular volcano-tectonic structures, represent very prominent surface expressions of mantle plume activity thus providing important clues for the understanding the tectonic evolution of the planet [1, 2]. They are commonly interpreted as forming in response to crustal stresses induced by an upwelling mantle plume, followed by gravitational relaxation or collapse associated with magma withdrawal [3].
Our findings allow to transition from reliance on numerical modeling to the direct investigation of coronae subsurface architecture using an observation-based geological dataset. This study examines fractures associated with seven coronae, spanning diameters from 115 km to 1070 km, capturing the coronae size variability: Atahensik, Demeter, Didilia, Heng-O, Kamui-Huci, Ninkarraka, and Pavlova. Fractal analyses of mapped fractures were performed to estimate the thickness of the fractured medium, with each fracture family comprising hundreds to thousands of features to ensure robust statistical significance. The results reveal distinct behaviors between fractures confined to the corona annulus and those extending beyond it, highlighting fundamental differences in their formation and evolution processes.
For coronae with diameters ≤320 km, fracturing systems within and along the annulus are confined to the crustal thickness [4,5] while maintaining a scaling relationship with the coronae diameter. This pattern suggests a unified formation mechanism operating across the entire volcano-tectonic structure. Such behavior is consistent with the hypothesis that diking driven by a mantle plume facilitates magma emplacement within the crust, resulting in the formation of shallower magma chambers. Magma withdrawal from these reservoirs, spanning from initial evolution to collapse, appears to govern the surface fracturing observed [6]. In contrast, larger coronae exhibit a thicker fractured medium beneath their central regions, indicating mechanical coupling between the crust and upper mantle. This coupling likely arises due to elevated strain rates, which may result either from interactions between the plume and lithosphere (i) during active plume uplift, where magma advection generates high strain rates, or (ii) during later stages of evolution, when the cooling of underplated magma drives rapid subsidence of the lithospheric block. The mechanical interplay between the crust and shallow mantle thus spans multiple evolutionary phases, facilitating the development of deep fracture systems similar to those observed on Venus. These findings align with the coexistence of both active and inactive coronae [7] identified within the dataset.
[1] Ghail, R. C., et al., Space Sci-ence Reviews 220.4 (2024): 36. [2] Phillips, R. J., J. Geophys. Res. 95, 1301–1316 (1990). [3] Janes, D. M., S. W. et al., J. Geophys. Res., 97(E10), 16,055– 16,067, (1992) [4] James, P.B., et al., 118, 859–875, (2013). [5] Ji-ménez-Díaz, A., et al., Icarus 260 (2015): 215-231. [6] Lang, N.P., and López, I., Geological Society, London, Special Pub-lications 401.1 (2015): 77-95. [7] Gülcher, A.J.P., et al., Nat. Geo. 13.8 (2020): 547-554.
Acknowledgement: This research was supported by the European Union NextGenerationEU pro-gramme and the 2023 STARS Grants@Unipd pro-gramme “HECATE”.
How to cite: De Toffoli, B. and Mazzarini, F.: Subsurface Architecture of Coronae, Venus , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17486, https://doi.org/10.5194/egusphere-egu25-17486, 2025.
Venus is similar to Earth in terms of mass and size and is sometimes also referred to as "Earth's twin". Nevertheless, there are some significant differences between the two planets such as their atmospheric mass and composition, geophysical activity, rotation, and magnetic field. The origins for the differences between the two planets are still unknown. Since giant impacts are expected to be common in the early evolution of the solar system, it is likely that Venus also experienced an impact. Giant impacts on Venus have likely played an important role in shaping its geological and atmospheric evolution, impacting factors such as volcanic activity and surface composition. Investigating such impact events could provide an improved understanding of Venus' present-day characteristics. Furthermore, contrasting the consequences of impacts on Venus and on other terrestrial planets like Earth and Mars provides a comparative framework for analyzing their histories, and valuable insights into the underlying factors that influence the evolution and the internal structure of terrestrial planets.In this research we explore a range of possible impacts on Venus and investigate their effects on Venus evolution. We present results from ultra-high resolution simulations of giant impacts on Venus using Smoothed Particle Hydrodynamics (SPH). Venus' interior pre-impact is assumed to consist of an iron core (30% of Venus' mass) and a forsterite mantle (70% of Venus' mass), where the planetary mass is set to be Venus' current mass. We also consider models where Venus has a primordial atmosphere with a mass of 1% of Venus' mass. We allow for different atmospheric compositions including: hydrogen, hydrogen-helium, water, CO and CO2. For the impactors we assume differentiated bodies with masses ranging from 1e-4 - 0.1 Earth masses. Impact velocities vary between 10 and 30 km/s, which translates to roughly 1 - 3 times Venus' escape velocity. We also consider different impact geometries (head-on and oblique) and a range of pre-impact rotation rates for Venus. We show how different impact conditions lead to different post-impact composition, thermal profiles and rotation periods. We also quantify atmospheric losses caused by the impacts in various scenarios, most relevant for highly energetic collisions. Finally, we use the impact results to infer the post-impact thermal profile of Venus and explore how it affects Venus' long-term thermal evolution and current-state internal structure. We then identify the impact scenarios that are most consistent with Venus' observed properties. Our research clearly demonstrates that an exploration of giant impacts on Venus can provide valuable insights into the fundamental processes shaping terrestrial planets. This understanding not only enhances our comprehension of planetary evolution within our solar system but also extends to terrestrial exoplanets.
How to cite: Bussmann, M., Helled, R., Gillmann, C., Tackley, P., Reinhardt, C., and Stadel, J.: Giant Impacts on Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17467, https://doi.org/10.5194/egusphere-egu25-17467, 2025.
One can separate the atmospheric evolution of Venus into two epochs. The first epoch lasts from the final accreted planet 4.5 Gyr ago to the "last" resurfacing that occurred about 200-1000 Myr ago. The second epoch lasts from this resurfacing event until today. The evolution of Venus’ atmosphere during the beginning of the first epoch was exposed by very high solar EUV flux values, probably, water that was produced from the interaction between a primordial atmosphere and a magma ocean, water that was incorporated into the planet’s accretion from carbonaceous chondrites or a mixture of both sources. The different water sources have different initial D to H ratios, which could have been fractionated due to atmospheric escape. Here we will investigate how thermal escape processes may have affected or modified water-based initial D/H ratios after the planet’s origin to the last resurfacing a few hundred Myr ago. By knowing the loss rates of H2O from the planet’s origin to the time when the "last" resurfacing occurred, including the corresponding D/H ratio, allows us to make statements about the planet's water balance, since the ratio evolution during the above-mentioned second epoch is dominated by photochemical non-thermal H and D loss processes.
How to cite: Lammer, H., Scherf, M., Erkaev, N. V., Johnstone, C., Van Looveren, G., Kislyakova, K. G., Weichbold, F., Constatinou, T., Woitke, P., Rimma, P., Ferrus, M., Eminger, P., and Nemeckova, K.: The evolution of Venus’ early water inventory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15793, https://doi.org/10.5194/egusphere-egu25-15793, 2025.
The neutral heating efficiency is commonly defined as the ratio of the net local gas-heating rate to the rate of solar radiative energy absorption. It is a crucial parameter that determines the upper atmospheric temperature and the thermal escape rate on both solar system bodies and exoplanets. In this study, we construct a one-dimensional photochemical model to compute the neutral heating efficiency in the dayside Venusian upper atmosphere. This calculation involves a complex network of microscopic processes, including photon and photoelectron impact processes, as well as exothermic chemical reactions. Our calculations indicate that the major heat sources in the Venusian atmosphere are the photodissociation of CO2 at lower altitudes and the dissociative recombination of O2+ at higher altitudes. During solar maximum, the neutral heating efficiency remains relatively constant at approximately 35% between 110 and 160 km, declining to 20% near 220 km. Furthermore, we find that the heating efficiency at higher altitudes is enhanced by increased concentrations of background H2, attributable to a higher abundance of O2+.
How to cite: Niu, D. and Cui, J.: Neutral Heating Efficiency in the Dayside Venusian Upper Atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14833, https://doi.org/10.5194/egusphere-egu25-14833, 2025.
Radiative Transfer (RT) modeling is an essential tool to understand planetary atmospheres. In the coming decade, several missions to Venus are planned that aim to image Venus nightside thermal emission in the NIR spectral windows [1]. The NIR wavelength range of 0.8–1.2 µm contains spectral windows where Venus’ surface thermal emission radiation is detectable from space, paving the way for surface and near-surface atmosphere studies in these bands [2]. In order to process the data from these missions once they are available, RT modeling of the Venusian atmosphere is a necessary first step. The Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus (SPICAV) suite on board Venus Express made observations of Venus’ nightside in the spectral range of 0.65–1.7 µm [3] and provides a good baseline for a comparison with synthetic spectra. These spectra are based on molecular absorption cross-sections which in turn are governed by the line list chosen for the model. The HIgh-resolution TRANsmission molecular absorption database (HITRAN) is a frequently used line database in RT modeling [4]. Several Venus atmospheric studies (e.g., [5]), however, have relied on the database of [2] for CO2 lines, referred to as “Hot CO2” from here on. Newer line databases have been developed for high temperature atmospheres which are yet to be applied to Venusian atmospheric studies [4]. As part of this work we model nadir radiances for the Venusian atmosphere in the NIR range using a DISORT [7] algorithm and compare them to radiances produced with existing RT schemes used for modeling atmospheres (e.g., Planetary Spectrum Generator (PSG) [8]). In this work:
- We compare radiances produced considering absorption from relevant species present in the Venusian atmosphere using different line-lists: HITRAN 2020, HITEMP, Hot CO2 [2,4,6].
- We compare our modeled radiances to the observed SPICAV dataset
- We make further comments and predictions regarding parameters that need to be fine-tuned in order to reproduce the observed spectra from SPICAV.
References:
[1] Allen D. A. et al. (1984) Nature, 307, 222–224
[2] Pollack J. B. et al. (1993) Icarus, 103, 1–42
[3] Korablev O. et al. (2006) J. Geophys. Res. 111(E9)
[4] Gordon I. E. et al. (2022) J. Quant. Spectrosc. Radiat. Transfer, 277, 107949
[5] Bézard B. et al. (2011) Icarus, 216(1), 173–83
[6] Rothman L. S. et al. (2010) J. Quant. Spectrosc. & Radiat. Transfer, 111(12-13), 2139–2150
[7] Stamnes et al. (1988) Applied Optics, 27(12), 2502-2509
[8] Villanueva G. L. et al. (2018) J. Quant. Spectrosc. & Radiat. Transfer, 217, 86 – 104
How to cite: Das, A., Mueller, N., Schreier, F., Kappel, D., Grenfell, J. L., Rauer, H., Plesa, A.-C., and Helbert, J.: Radiative Transfer Modeling of Venus - A comparison of line databases, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18202, https://doi.org/10.5194/egusphere-egu25-18202, 2025.
In this work, we show that Venus’ aerosols possess a complex chemical composition and contain previously underestimated reservoirs of water and iron sulfate. These assessments are based on re-analyses of data acquired in Venus’ atmosphere in 1978 by the Pioneer Venus Large Probe (PVLP). Data from the Large Probe Neutral Mass Spectrometer (LNMS) and Gas Chromatograph (LGC) are consistent with evolved gas analysis. During descent through the clouds, aerosols likely collected into the intake inlet assemblies of the LNMS and LGC. The collected aerosols then differentially decomposed through the increasingly hot atmosphere and released gases into the LNMS and LGC. Our treatment of LNMS data indicates that aerosols from ~ 51-48 km contain sulfuric acid (H2SO4) and iron sulfate(s) (e.g., Fe2(SO4)3) in similar masses (~ 1 mg m-3) and 3-fold higher abundances of H2O (~ 3 mg m-3). The substantial aerosol-phase H2O likely arises from hydrates such as hydrated sulfates of iron and magnesium. Our inferred total aerosol mass loading, H2SO4 mass loading, and relative abundances of H2SO4 and H2O in the volatile fraction of the aerosol (sulfuric acid solution) are consistent with all preceding measurements. We suggest that all direct measurements conducted in Venus’ clouds – to date – sampled and analyzed the cloud aerosols. Aerosol-phase H2O was likely measured by the LNMS, LGC (Oyama et al., JGR, 85, 1980), Venera 13 and 14 gas chromatographs (Gel'man et al., Cosm. Res., 17, 1980, Mukhin et al., Sov. Astron. Let., 8, 1982), Venera 13 and 14 hygrometers (Surkov et al., Sov. Astron. Lett.l, 8, 1982), and Vega 1 and 2 moisture meters (Surkov et al., JGR Solid Earth, 91, 1986) – which independently measured high abundances of water in the clouds. Aerosol-phase iron was likely measured by the LNMS and suggested by X-ray radiometric data from Venera 12 (Petryanov et al., Soviet Physics Doklady, 260, 1981) and Vega 1 and 2 (Andreichikov et al., Cosm. Res., 25, 1987). Hence, these combined assessments highlight reservoirs of bulk water, iron sulfate, and possible cosmic materials (e.g., Fe and Mg) in Venus’ aerosols. This aerosol composition presents new considerations for Venus’ cloud chemistry, spectroscopy (e.g., refractive index and UV absorption), and habitability assessments. Further, these results apply to the upcoming DAVINCI mission and Venus Orbiter Mission, which plan to sample within and above the clouds, respectively.
How to cite: Mogul, R., Zolotov, M., Way, M., and Limaye, S.: Venus’ Aerosol Composition Extracted from Pioneer Venus Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2625, https://doi.org/10.5194/egusphere-egu25-2625, 2025.
