TP2

The evolution of surface conditions on Venus has recently made a return to the forefront of planetary sciences questions. Due to both the striking similarities and the obvious differences between Earth and Venus, understanding Venus might hold some of the keys to how terrestrial planets become habitable, either in our solar system or beyond. The question of the origin and persistence of water at the surface/in the atmosphere of Venus determines, in a large part what the planet's evolutionary path has been. The critical difference between Earth and Venus might even be settled during their primordial evolution. Since no sample of Venus can be studied yet, as would be the case for Earth, we turn on alternative methods of investigation. We track the evolution of volatiles at the surface of the planet during its history, since the end of the magma ocean phase. We compare these scenarios with present-day observation and derive limits on maximum amounts of volatiles in the atmosphere of Venus through time, on volatile exchanges, and on water delivery.  

We have developed coupled numerical simulations of the evolution of Venus, modeling mechanisms that govern its surface conditions and atmosphere composition. Currently, the simulations include modeling of mantle dynamics, core evolution, volcanism, surface alteration, atmospheric escape (both hydrodynamic and non-thermal), greenhouse effect, and the feedback mechanisms between the interior and the atmosphere of the planet. Focusing on Late Accretion, we have modeled the effects of large meteoritic impacts on long term evolution through three aspects: atmosphere erosion, volatile delivery and mantle dynamics perturbation due to energy transfer.  The models are constrained by present-day observation and atmosphere composition, with the requirement that scenarios fit reasonnably the current state of the planet.

We produce scenarios that fit present-day conditions and feature both early mobile lid regime (akin to plate tectonics) as well as late episodic lid regime with resurfacing events. However, water outgassing during late evolution could be dampened by high surface pressures. Therefore, it is during the early history of Venus, in particular, that we observe the largest volatile exchanges. That era seems to have large repercussions on long term evolution and present-day state, as it determines volatile inventories and repartition.

The effects of impacts dominate the volatile and mantle evolution during Late Accretion. Large impacts are shown to have essential consequences for volatile repartition. The atmosphere erosion they cause is marginal and doesn’t deplete the atmosphere as much as swarms of smaller bodies, they instead act as a significant source of volatiles. Indeed, if Late Accretion is mainly composed of volatile-rich bodies; it is very difficult to reach the observed present-day state of Venus; instead the atmosphere may become too wet. Likewise, the likely mass received by Venus during volatile-rich Late Accretion, if completely outgassed into the planet's atmosphere, could lead to masses of CO₂ and N₂ 3-6 times higher than observed at present-day.

Simulations show that the maximum contribution of wet material impactors (carbon-chondrites-like) is about 5-10% (mass.) of the total accreted mass during Late Accretion (the larger portion of the Late accretion being composed of enstatite-chondrite-like bodies). In less volatile rich scenarios, water brought by collisions is then lost, either quickly or over billions of years. A small amount of water is then slowly reinserted in the atmosphere by volcanic outgassing.

In wet scenarios, water is efficiently brought to the surface of Venus and loss mechanisms are not able to remove it later, through solid surface oxidation and atmospheric escape. This then leads to water-rich atmosphere, unlike what we observe today.

Those results are consistent over a large range of simulations with variations of late accretion timing, impactors mass-size distribution, composition, efficiency, mantle parameters and so on. Water should have been delivered early to the terrestrial planets in the solar system, during main accretion, before the last giant impact, as is suggested for Earth from isotopic measurements. 

Acknowledgments: CG acknowledges support from the FNRS ET-HOME project and Brussels Free University. CG further acknowledges support from the CLEVER Planets group, supported by NASA.

How to cite: Gillmann, C., Golabek, G., Raymond, S., Tackley, P., Schoenbaechler, M., Dehant, V., and Debaille, V.: The Consequences of Late Accretion Volatile Delivery and Loss Mechanisms on Venus’ Evolution, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-62, https://doi.org/10.5194/epsc2022-62, 2022.

Venus appears to be an “alien” planet drastically and surprisingly different from the Earth. The early space missions revealed the world with remarkably hot, dense, cloudy, and very dynamic atmosphere filled with toxic species likely of volcanic origin. During more than 8 years of operations ESA’s Venus Express spacecraft performed a global survey of the atmosphere and plasma environment of our near neighbour. The mission delivered comprehensive data on the temperature structure, the atmospheric composition, the cloud morphology, the atmospheric dynamics, the solar wind interaction and the escape processes. Vertical profiles of the atmospheric temperature showed strong latitudinal trend in the mesosphere and upper troposphere correlated with the changes in the cloud top structure and suggesting convective instability in the main cloud deck at 50-60 km. Observations revealed significant latitudinal variations and temporal changes in the global cloud top morphology, which modulate the solar energy deposited in the atmosphere. The cloud top altitude varies from ~72 km in the low and middle latitudes to ~64 km in the polar region, correlated with decrease of the aerosol scale height from 4 ± 1.6 km to 1.7 ± 2.4 km, marking vast polar depression. UV imaging showed for the first time the middle latitudes and polar regions in unprecedented detail. In particular, the eye of the Southern polar vortex was found to be a strongly variable feature with complex dynamics.

Solar occultation observations and deep atmosphere spectroscopy in spectral transparency “windows” mapped distribution of the major trace gases H₂O, SO₂, CO, COS and their variations above and below the clouds, revealing key features of the dynamical and chemical processes at work. A strong, an order of magnitude, increase in SO₂ cloud top abundance with subsequent return to the previous concentration was monitored by Venus Express specrometres. This phenomenon can be explained either by a mighty volcanic eruption or atmospheric dynamics.

Tracking of cloud features provided the most complete characterization of the mean atmospheric circulation as well as its variability. Low and middle latitudes show an almost constant with latitude zonal wind speed at the cloud tops and vertical wind shear of 2-3 m/s/km. Surprisingly the zonal wind speed was found to correlate with topography decreasing from 110±16 m/s above lowlands to 84±20 m/s at Aphrodite Terra suggesting decelerating effect of topographic highs. Towards the pole, the wind speed drops quickly and the apparent vertical shear vanishes. The meridional cloud top wind has poleward direction with the wind speed ranging from about 0 m/s at equator to about 15 m/s in the middle latitudes. A reverse equatorward flow was found about 20 km deeper in the middle cloud suggesting existence of a Hadley cell or action of thermal tides at the cloud level. Comparison of the thermal wind field derived from temperature sounding to the cloud-tracked winds confirms the validity of cyclostrophic balance, at least in the latitude range from 30S to 70S. The observations are supported by the General Circulation Models.

Venus Express detected and mapped non-LTE infrared emissions in the lines of O₂, NO, CO₂, OH originating near the mesopause at 95-105 km. The data show that the peak intensity occurs in average close to the anti-solar point for O₂ emission, which is consistent with current models of the thermospheric circulation. For almost complete solar cycle the Venus Express instruments continuously monitored the induced magnetic field and plasma environment and established the global escape rates of 3·10²⁴s⁻¹, 7·10²⁴s⁻¹, 8·10²²s⁻¹ for O⁺, H⁺, and He⁺ ions and identified the main acceleration process. For the first time it was shown that the reconnection process takes place in the tail of a non-magnetized body. It was confirmed that the lightning tentatively detected by Pioneer-Venus Orbiter indeed occurs on Venus.

Thermal mapping of the surface in the near-IR spectral “windows” on the night side indicated the presence of recent volcanism on the planet, as does the high and strongly variable SO₂ abundance. Variations in the thermal emissivity of the surface observed by the VIRTIS imaging spectrometer indicated compositional differences in lava flows at three hotspots. These anomalies were interpreted as a lack of surface weathering suggesting the flows to be younger than 2.5 million years indicating that Venus is actively resurfacing. The VMC camera provided evidence of transient bright spots on the surface that are consistent with the extrusion of lava flows that locally cause significantly elevated surface temperatures. The very strong spatial correlation of the transient bright spots with the extremely young Ganiki Chasma, their similarity to locations of rift-associated volcanism on Earth, provide strong evidence of their volcanic origin and suggests that Venus is currently geodynamically active.

Alongside observations of Earth, Mars and Titan, observation of Venus allows the opportunity to study geophysical processes in a wide range of parameter space. Furthermore, Venus can be considered as an archetype of terrestrial exoplanets that emphasizes an important link to the quickly growing field of exoplanets research.

The talk will give an overview of the Venus Express findings including recent results of data analysis, outline outstanding unsolved problems and provide a bridge, via the Akatsuki mission, to the missions to come in 2030s: EnVision, VERITAS and DAVINCI.

How to cite: Titov, D., Straume-Lindner, A. G., and Wilson, C.: Venus Express as precursor of the Venus Decade, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1120, https://doi.org/10.5194/epsc2022-1120, 2022.

VERITAS is a NASA Discovery mission that was selected on June 2, 2021 and is a partnership between scientists and engineers at NASA/JPL and with the German (DLR), Italian (ASI) and French Space Agencies (CNES). VERITAS would carry two instruments, VISAR, an X-band interferometric radar provided by NASA/JPL with contributions from ASI and DLR, and VEM, an infrared spectrometer provided by DLR. Data from these two instruments would be combined with gravity science data obtained from telecom tracking data to investigate tectonic style and ongoing volcanism. Science data is collected in two phases after arriving at Venus after a 7-month cruise from Earth. During the second phase of science data collections VERITAS plans to collect radar data for image generation, topographic mapping and targeted repeat pass radar interferometry observations to measure surface deformation .

VERITAS has two phases of science operation. The first science phase (SP1) for VEM operations occurs during a 4-month interruption in the middle of 16 month aerobraking phase, which is needed to achieve the desired circular orbit needed for Science Phase 2 observations of both the VISAR and VEM instruments. The final nearly circular polar orbit used for SP2 varies between 180 and 255 km in altitude. SP2 lasts for 4 Venus sidereal days or ‘cycles’, each of which is 243 days in duration owing to the very slow rotation rate of Venus. The orbit is designed as a frozen eccentricity orbit so that its trajectory nearly repeats from cycle to cycle to facilitate repeat pass radar observations.

VISAR nominally collects data for 11 orbits on both ascending and descending passes followed by 5 orbits of data downlink to Earth. Data is processed onboard to multi-looked imagery and interferograms to reduce the data downlink volume up to 1000 fold. The exception to this is when repeat pass radar interferometry (RPI) data is collected for targeted sites on the surface. Since RPI sites are 200 km (along-track) × 200 km (cross-track) in extent, raw data for 20 consecutive orbits (Venus rotates 10 km at the equator during a VERITAS orbit) are needed to map a site. Raw data are downlinked for processing on Earth. Downlinked data volume as well as ∆V and other operational considerations limit the number of RPI sites to approximately12-18.

Fig. 1: VISAR flight configuration and observing geometry are optimized for InSAR DEM acquisition with baseline separation B = 3.1 m.

Venus is expected to be active today. VERITAS requires detection of 2-cm deformations for spatial scales of 1 km (e.g., fault creep) and 2 cm at 40 m horizontal postings for small-scale (e.g., volcanic) features. To access which deformation signals would be discernible given the expected amount of atmospheric noise we simulated volcanic deformation using various localized, spherical sources (a.k.a. Mogi sources) for a range of source depth and delta volumes. We assumed Earth-like magma chambers at depths of 2-28 km and delta volumes of 1-48 km³, in reasonable agreement with the few Venusian volcanoes for which these parameters can be estimated. Figure 2 shows that inflation above magma chambers at a range of depths, even including atmospheric variability, produces a readily discernible deformation exceeding 2 cm, assuming 1.5 cm of atmospheric distortion at 200 km length scale.

Fig. 2: Deformations above 2 cm are detectable with VISAR RPI techniques, after accounting for observed S02 variability. Left: Fringe patterns (2 cm of deformation per color cycle) for 30 Mogi point sources with atmospheric distortion superimposed. Right: De formation above or near the detectability limit are shown as green dots; those obscured by atmospheric distortion are red.

Radar image, topographic and RPI data along with data from the VEM instrument and gravity measurements to answer three essential science questions: 1) What processes shape rocky planet evolution? 2) What geologic processes are currently active? and 3) Is there evidence of past and present interior water? VERITAS’ VISAR instruments is integral to endind many 30-year-old debates for Venus, such as whether volcanism has been steady or catastrophic, why it lacks terrestrial-style plate tectonics, how it loses its heat, and if it has continents.

A portion of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

How to cite: Hensley, S., Smrekar, S., Campbell, B., Mastrogiuseppe, M., Perkovic-Martin, D., Younis, M., and Zebker, H.: VERITAS Radar Observations at Venus, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-751, https://doi.org/10.5194/epsc2022-751, 2022.

EnVision was selected as ESA's 5th Medium-class mission in the Agency's Cosmic Vision plan, targeting a launch in the early 2030s. EnVision's overarching science questions are to explore the full range of geoscientific processes operating on Venus. It will investigate Venus from its inner core to its atmosphere at an unprecedented scale of resolution, characterising in particular core and mantle structure, signs of past geologic processes, and looking for evidence of past liquid water. Far more than a simple radar mission, this suite of investigations works together to comprehensively assess surface and subsurface geological processes, interior geophysics and geodynamics, and atmospheric pathways of key volcanogenic gases, which together illuminate how and why Venus turned out so differently to Earth. Recent modeling studies strongly suggest that the evolution of the atmosphere and interior of Venus are coupled, emphasizing the need to study the atmosphere, surface, and interior of Venus as a system. 

EnVision is an ESA Venus orbiter mission formulated in collaboration with NASA; As a key partner in the mission, NASA provides the Synthetic Aperture Radar, VenSAR. The EnVision payload consists of five instruments provided by European and US institutions. The five instruments comprise a comprehensive measurement suite spanning infrared, ultraviolet- visible, microwave and high frequency wavelengths, complemented by the Radio Science investigation exploiting the spacecraft TT&C system. All instruments in the payload have substantial heritage and robust margins relative to the requirements with designs suitable for operation in the Venus environment. This suite of instruments was chosen to meet the broad spectrum of measurement requirements needed to support EnVision science investigations.

How to cite: Widemann, T., Straume-Lindner, A. G., Ocampo, A. C., Voirin, T., Vandaele, A. C., Moreira, A., Campbell, B., Dumoulin, C., Marcq, E., Gilli, G., Helbert, J., Kiefer, W., Carter, L., Bruzzone, L., Mason, P., Hensley, S., and Bocanegra-Bahamon, T.: EnVision: understanding why our closest neighbour is so different, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1097, https://doi.org/10.5194/epsc2022-1097, 2022.

EnVision is a Venus orbiter mission that will determine the nature and current state of geological processes on Venus in the present era, measure how those processes generate and sustain the inhospitable atmosphere and climate of Venus, and piece together the sequence of events – the geological history – that led to that current state. Envision was selected in June 2021 to become the next M-Class mission of ESA's Cosmic Vision Programme. To full fill the science objectives, EnVision employs a suite of instruments optimised for observations from Venus orbit, including an imaging radar for high-resolution surface mapping (provided by NASA), a sounding radar for discerning the geometry of the near subsurface, a multispectral infrared camera capturing the composition of surficial rocks and atmospheric composition, and an infrared and ultraviolet spectrometer, complemented by radio science experiments, to identify the pathways of important volcanogenic gases (water vapour, sulphur dioxide, and others) from the lower atmosphere up and into the clouds and in the upper atmosphere. The radoscience experiment also exploits the precise orbit determination to measure the gravity field and probe the deep interior structure of Venus. Figure 1 shows the instrument payload integrated onto the spacecraft and the country and organization responsible for each payload element. The Synthetic Aperture Radar, VenSAR, will image pre-selected regions of interest at a resolution of 30 m/pixel, and subregions at 10 m/pixel. EnVision will be the first Venus mission hosting a Subsurface Radar Sounder, SRS, characterizing the vertical structure and stratigraphy of geological units including volcanic flows. The spectrometer suite, VenSpec, will obtain global maps of surface emissivity in six wavelength bands using one ultraviolet on the dayside, and five near-infrared spectral transparency windows in the nightside atmosphere, to constrain surface mineralogy and inform evolutionary scenarios; and measure variations of SO2, SO and linked gases in the mesosphere. These variations will be further linked to tropospheric variations and volcanism. The Radio Science Experiment uses the spacecraft-Earth radio link for gravity mapping and atmospheric profiling. EnVision is planned to be launched on an Ariane 62 in 2031 with back-up launch dates in 2032 and 2033. An interplanetary cruise is followed by orbit insertion and then circularisation by aerobraking to achieve the nominal science orbit, a low quasi-polar Venus orbit. NASA is contributing the VenSAR instrument and supplies DSN support. The other payload instruments are contributed by ESA member states, with ASI, DLR, BelSPO, and CNES leading the procurement of SRS, VenSpec-M, VenSpec-H, the USO and VenSpec-U instruments respectively.

Figure 1 EnVision' s payload instruments integrated onto the spacecraft

How to cite: Straume-Lindner, A.-G., Buchwald, R., Crouzet, P.-E., Titov, D., Voirin, T., and Wielders, A.: EnVision: An ESA Medium-class mission to Venus in collaboration with NASA, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-196, https://doi.org/10.5194/epsc2022-196, 2022.

The VenSpec instrument suite on the EnVision mission consists of three channels: VenSpec-M, VenSpec-H, VenSpec-U, and the Central Control Unit (CCU).

VenSpec-H will be dedicated to high-resolution atmospheric measurements. The main objective of the VenSpec- H instrument is to detect and quantify SO2, H2O and HDO in both the troposphere and the mesosphere, to enable characterization of volcanic plumes and other sources of gas exchange with the surface of Venus, complementing VenSAR and VenSpec-M surface, SRS subsurface observations and VenSpec-U observations in the upper cloud layer. A nadir pointed high-resolution infrared spectrometer is the ideal instrument for these observations in different spectral windows between 1 and 2.5 microns, that permit measurements of the troposphere during the night, and of the mesosphere during the day. VenSpec-U will monitor sulphur-bearing minor species (mainly SO and SO2) and the yet unknown UV absorber in Venusian upper clouds and just above. It will therefore complement the two other channels by investigating how the upper atmosphere interacts with the lower atmosphere, and especially characterize to which extent outgassing processes such as volcanic plumes are able to disturb the atmosphere through the thick Venusian clouds. The twin channel (0.2 nm in high-resolution, 2 nm in low-resolution) spectral imager in the 190-380 nm range able to operate in nadir is ideally suited to such a task.

VenSpec-M will provide near-global compositional data on rock types, weathering, and crustal evolution by mapping the Venus surface in five atmospheric windows. The broadest window at 1.02 μm is mapped with two filters to obtain information on the shape of the window. Additional filters are used to remove clouds, water, and stray light. VenSpec-M will use the methodology pioneered by VIRTIS on Venus Express but with more and wider spectral bands, the NASA VERITAS VIRSAR and Envision VenSAR-derived DEMs, and EnVision’s lower orbit compared to Venus Express to deliver near-global multichannel spectroscopy with wider spectral coverage and an order of magnitude improvement in sensitivity. It will obtain repeated imagery of surface thermal emission, constraining current rates of volcanic activity following earlier observations from Venus Express. In combination with the observations provided by the identical VEM instrument on the NASA VERITAS mission VenSpec-M will provide more than a decade of monitoring for volcanic activity, as well as search for surface changes.

In combination, VenSpec spectrometers will provide unprecedented insights into the current state of Venus and its past evolution. VenSpec will perform a comprehensive search for volcanic activity by targeting atmospheric signatures, thermal signatures and compositional signatures, as well as a global map of surface composition. VenSpec will be key to studying the coupled system of surface and atmosphere on Venus following the holistic approach of Envision.

How to cite: Helbert, J., Vandaele, A.-C., Marcq, E., Roberts, S., Neefs, E., Erwin, J., Guignan, G., Lustrement, B., Peter, G., Rockstein, S., Wolff, F., Alemanno, G., Lara, L., Castro, J., Lasue, J., and Vinatier, S. and the The VenSpec team: The VenSpec suite on the ESA Envision mission – a holistic investigation of the coupled surface atmosphere system of Venus, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-374, https://doi.org/10.5194/epsc2022-374, 2022.

EnVision has been selected in the M5 call of ESA’s Cosmic Vision program as the next European led mission to Venus. It is dedicated to unravel some of the numerous open questions about Venus' past, current state and future and will help to understand why Venus and Earth evolved so differently.

The Radio Science Experiment (RSE) on EnVision will perform extensive studies of the gravitational field but also Radio Occultations to sense the Venus atmosphere and ionosphere at a high vertical resolution of only a few hundred metres. These radio occultations provide electron density profiles in the ionosphere and atmospheric density, temperature and pressure profiles in the upper troposphere and mesosphere (~40 – 90 km). Additionally, they allow to study the H₂SO₄ absorption in the Venus cloud layer.

The first radio occultation experiment at Venus was conducted during the Mariner 5 flyby in 1967, followed by Mariner 10, several Venera missions, Magellan, and the Pioneer Venus Orbiter, and Akatsuki. The most extensive radio occultation study of the Venus atmosphere so far was carried out by the VeRa experiment on Venus Express.

EnVision will use two coherent frequencies (X- and Ka-band) to separate dispersive and nondispersive effects. This allows to distinguish between ionospheric wave structures and other noise induced effects in the ionosphere.

The use of Ka-band, which has never been used to sense the Venus atmosphere before, allows to study the H₂SO₄ absorption in the Venus cloud layer due to its high sensitivity to sulfuric acid absorption. Ka-band is also sensitive to liquid H₂SO₄ which provides the opportunity (in combination with X-band) to distinguish between gaseous and liquid H₂SO₄ absorption features on Venus for the very first time.

The short orbital period of EnVision in combination with its very small orbital inclination allows to cover all latitudes, longitudes, local times and solar zenith angles on Venus. Especially short-term variations caused by atmospheric waves can be identified to study traveling or stationary small scale atmospheric structures.

How to cite: Tellmann, S., Oschlisniok, J., Pätzold, M., Dumoulin, C., and Rosenblatt, P.: Radio Sounding of the Venusian Atmosphere and Ionosphere with EnVision, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-860, https://doi.org/10.5194/epsc2022-860, 2022.

Venus Dynamics Tracer (VdT) is a proposal for a multi-balloon mission to Venus that was submitted as a response to the ESA call for new M-class missions. This presentation discusses the science questions that could be addressed using two balloons at different altitudes in Venus atmosphere together with an orbiter. The main goal of VdT is to reveal how the atmospheric motion in the Venus atmosphere is driven by the energy originating from absorption of solar radiation. VdT achieves this by in situ measurements in two major regions where driving “motors” are located: Firstly, the cloud layer where visible light is absorbed and drives the vertical motions of the air. Secondly, the upper atmosphere where EUV is absorbed both by neutrals and ions and where energy and momentum are transferred between them. VdT combines the in situ measurements by two balloons at different altitudes in the atmosphere with in situ and remote sensing observations from an orbiter. The mission aims to answer the following questions: 1. What are the roles of the vertical and meridional circulation in maintaining major atmospheric dynamics near the clouds, including the superrotation? and 2. What is the global dynamics of ions and neutrals in the upper atmosphere?

VdT has only 50 kg scientific payload but enables break-through science by a unique distribution of the payload: 40 kg on an orbiter and 5 kg each on two atmospheric balloons. The presentation describes and motivates the suggested payload.

How to cite: Stenberg Wieser, G. and Persson, M.: Venus Dynamics Tracer - exploring Venus with balloons, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-588, https://doi.org/10.5194/epsc2022-588, 2022.

The possibility of life in the lower Venusian atmosphere has been given serious scientific consideration for many decades (Sagan, 1961; Cockell, 1999; Grinspoon, 1997; Schulze-Makuch and Irwin, 2002; Schulze-Makuch et al., 2004; Limaye et al., 2018; Limaye et al., 2021; Seager et al., 2021; Bains et al. 2021; Schulze-Makuch, 2021). More recently the idea has come to the forefront of astrobiological attention due to the claimed detection of the biomarker phosphine in the Venusian atmosphere (Greaves et al., 2021a). Whether or not phosphine has been detected is controversial; and if it has, it's significance is also controversial (Villanueva et al., 2021; Lincowski et al., 2021; Greaves et al., 2021b), as is the notion that life can exist in the Venusian atmosphere at all (Kasting and Harman, 2021).

If there is life in the clouds, it almost certainly resides within liquid droplets in the atmosphere (Schulze-Makuch and Irwin, 2004; Irwin and Schulze-Makuch, 2011; Schulze-Makuch, 2021), and most likely within mode 3 particles. Mode 3 particles are aerosols enriched in the lower cloud layer, about the size that would be expected for microbes if covered by a layer of inorganic compounds – including elemental sulfur and hydrophilic filaments. The Venus Pioneer probe made an attempt to identify the interior of these particles in the late 1980s, but unfortunately the pyrolyzer to crack open the particles jammed. This was unfortunate because an organic interior would have been a strong indication for possible life. Even if the cloud particles are not organic and show no evidence of living organisms, they would reveal critical insights about the natural history of Venus.  

Only new missions will provide clarity on whether the Venusian clouds are habitable and could possibly host living organisms. Two missions by NASA and one by ESA are currently in the planning stages to obtain more insights on the environmental conditions and potential habitability of the Venusian clouds. The results of these missions will surely reveal many important insights, but we propose here the more direct approach of collecting cloud droplets within the Venusian atmosphere with a return to Earth for their analysis. We have considered both an in-situ life detection and a sample return approach to resolve the question of whether the lower Venusian atmosphere may contain life.  Critical to both approaches is that the interior of the cloud droplet particles be analyzed.  The obvious instrument for the molecular analysis would be a gas chromatograph mass spectrometer (GC-MS) similar to the one used by the Curiosity Rover on Mars but including such an instrument for an in-situ life detection experiment would likely be weight-prohibitive.

Thus, we conclude that a sample return mission would seem to be more appropriate as this would also allow a much more detailed investigation of the cloud particles. If organic compounds are detected, a detailed analysis of the molecules and possible macromolecules can be conducted to determine whether the biochemical building blocks of Venusian life differ from those of life on Earth.  If not, we will obtain important insights about the natural history of Venus. Of the different mission approaches for a sample return which have been proposed, we have concluded that the NUVOLE SRS mission architecture based on a glider concept (Sindoni et al., 2021) is currently the most suitable approach.

References:

Bains W., Petkowski J.J., et al. (2021) Production of ammonia makes Venusian clouds habitable and explains observed cloud-level chemical anomalies. Proc. Natl. Acad. Sci. USA, 118.

Cockell C. S. (1999) Life on Venus. Planet. Space Sci., 47: 1487-1501.

Greaves J.S., Richards A.M.S., et al. (2021a) Phosphine gas in the cloud decks of Venus. Nature Astronomy, 5: 655-664.

Greaves J.S., Richards A.M.S., et al. (2021b) Addendum: Phosphine gas in the cloud deck of Venus. Nature Astronomy, 5: 726-728.

Grinspoon D.H. (1997) Venus Revealed: A New Look Below the Clouds of Our Mysterious Twin Planet. Perseus Publishing, Cambridge, Massachusetts.

Irwin L. N., and Schulze-Makuch D. (2011) Cosmic Biology: How Life Could Evolve on Other Worlds. Praxis, New York.

Kasting J.F., and Harman C.E. (2021) Venus might never have been habitable. Nature, 598: 259-260.

Limaye S.S., Mogul R., et al. (2021) Venus, an Astrobiology Target. Astrobiology, 21: 1163-1185.

Limaye S. S., Mogul R., et al. (2018) Venus' Spectral Signatures and the Potential for Life in the Clouds. Astrobiology, 18: 1181-1198.

Lincowski A.P., Meadows V.S., et al. (2021) Claimed detection of PH3 in the clouds of Venus is consistent with mesospheric SO2. Astrophys. J. Lett., 908: L44.

Sagan C. (1961) The planet Venus. Science, 133: 849-858.

Schulze-Makuch D. (2021) The case (or not) for life in the Venusian clouds. Life, 11: 255. https://doi.org/10.3390/life11030255.

Schulze-Makuch D., Grinspoon D.H., et al. (2004) A sulfur-based survival strategy for putative phototrophic life in the Venusian atmosphere. Astrobiology, 4: 11-18.

Schulze-Makuch D., and Irwin L.N. (2002) Reassessing the possibility of life on Venus: proposal for an astrobiology mission. Astrobiology, 2: 197-202.

Schulze-Makuch D., and Irwin L.N. (2004) Life in the Universe: Expectations and Constraints. Springer-Verlag, Berlin.

Seager S., Petkowski J.J., et al. (2021) The Venusian lower atmosphere haze as a depot for desiccated microbial life: A proposed life cycle for persistence of the Venusian aerial biosphere. Astrobiology, 21: 1206-1223.

Sindoni E., Vignaud P., et al. (2021) Feasibility study of a Venus atmosphere sample retrieval mission. In: 72nd International Astronautical Congress (IAC), IAC-21-A2.5.2., Dubai, United Arab Emirates.

Villanueva G.L., Cordiner M., et al. (2021) No evidence of phosphine in the atmosphere of Venus from independent analyses. Nature Astronomy, 5: 631-635.

How to cite: Schulze-Makuch, D., Irwin, L., and Irwin, T.: The Case for a Mission to Return Cloud Particles from the Lower Atmosphere of Venus, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-77, https://doi.org/10.5194/epsc2022-77, 2022.

One of the most informative ways of studying the interior structure and geodynamics of terrestrial planets is the joint investigation of gravity and topography data. In the case of Venus, this is in fact one of the only sources of information about the planet's interior, along with the lack of an active dynamo (e.g., Phillips and Russell, 1987), estimations of the moment of inertia (Margot et al., 2021) and tidal love numbers (Konopliv and Yoder, 1996). The firsts global gravity-topography analyses of Venus revealed unique characteristics. For long wavelengths, the planet presents correlations which are considerably higher than for Earth (Sjogren et al., 1980). Moreover, the apparent depth of compensation is large, globally deeper than 100 km (e.g., Kiefer et al., 1986). By analyzing the wavelength-dependent ratio between gravity and topography, the so-called spectral admittance, Kiefer et al. 1986 concluded that Venus' long-wavelength topography is mostly supported dynamically, i.e., by convective flows in the mantle.

Although today we know that some Venusian highlands, such as the crustal plateaus (e.g., Simons et al., 1997, Maia and Wieczorek, 2022) and Ishtar Terra (e.g., Kucinskas et al., 1996), are more consistent with being in a state of isostasy with significant variations on crustal thickness, it is broadly accepted that dynamic compensation is important on a global scale, notably at long wavelengths. Hence, one can attempt to predict Venus' gravity field and surface displacement using a geophysical model of mantle convection and how this couples to the surface. One of the most used instantaneous dynamic loading models was developed by Hager and Clayton (1989), where mantle flows, triggered by density anomalies, depend on radial viscosity variations.  On Venus, this model has been adopted to estimate mantle mass anomalies maps and to investigate the planet's mantle viscosity profile (e.g., Herrick and Phillips, 1992; Pauer et al. 2006; James et al. 2013).  Herrick and Phillips (1992) conclude that Venus mantle is consistent with a constant viscosity profile while Pauer et al. (2006) suggests that Venus could be more similar to Earth, where the mantle viscosity increases with depth and with a possible low-viscosity zone in the upper mantle.

These studies investigate the global topography and gravity signals to make their predictions. However, there are major highlands on Venus, such as Ovda, Thetis and Ishtar Terra, that are inconsistent with dynamic support. Using the Hager and Clayton (1989) dynamic model we do a new mantle viscosity investigation that excludes those areas where the gravity and topography signals are best modeled by a combination of Airy isostasy and lithospheric flexure. Our study is performed in the spectral domain and a multitaper spatio-spectral localization approach (Wieczorek and Simons, 2007) is adopted to suppress the signals of Ishtar Terra and Western Aphrodite Terra. The figure below shows a comparison between Venus global spectral admittance and correlation and the tapered estimations. There is a clear increase in admittance and correlation when the localization tapers are applied, specially for long wavelengths where dynamic loading is expected to dominate. The difference is largely attributed to the high elevations associated with the highlands that are near a state of isostasy, and hence have low associated gravity signals.

Regarding the dynamic modeling, we consider a viscosity profile with four layers, where the viscosity and depth of each layer are randomly sampled following a log-uniform and a uniform distribution, respectively. After computing the predicted topography and gravity field, we multiply the data by several different orthogonal localization windows and calculate the predicted admittance.  The misfits between observations and predictions are computed in order determine the accepted models and constrain the mantle viscosity structure.

The range of models that properly fit the observed admittance can be roughly divided into two groups, illustrated in figure below. The first is overall characterized by a layer of relative low viscosity beneath the lithosphere with maximum thickness of about 400 km, followed by an increase of viscosity with depth down to the core-mantle boundary. The second set of models does not present a clear viscosity boundary between the lithosphere and the underlying mantle and, as for the first group, the viscosity tends to increase with depth. In this scenario, however, a large number of models present a basal low viscosity zone in the mantle with thicknesses ranging from about 300 to 1000 km. In the next steps of our study, we intend to pinpoint what is the most likely viscosity structure of Venus’ mantle, interpreting the results in the framework of a Bayesian analysis to assess the likelihood of each of these scenarios and considering the physical implications of the different models.

Hager, B. and Clayton, R. (1989) Mantle Convection, 657-763; Herrick, R. and Phillips, R. (1992) JGR, 97; James, P. et al. (2013) JGR-Planets, 118; Kiefer et al. (1986) GRL, 13; Konopliv and Yoder (1996) GRL, 23; Kucinskas et al. (1996) JGR, 101; Maia and Wieczorek (2022) JGR-Planets, 127; Margot et al. (2021) Nat Astron; Pauer et al. (2006) JGR, 111; Phillips and Russel (1987); Simons et al. (1997) JGI, 131; Sjogren et al. (1980) JGR, 85; Wieczorek and Simons (2007) J Fourier Anal Appl, 13

How to cite: Maia, J. and Wieczorek, M.: Towards new insights of Venus mantle viscosity structure, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-407, https://doi.org/10.5194/epsc2022-407, 2022.

How to cite: Kulkarni, S., Wilson, C., and Irwin, P.: Investigating the properties of a near-surface cloud layer from Venera 13 and 14 descent probe data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1121, https://doi.org/10.5194/epsc2022-1121, 2022.

The 2-µm infrared camera (IR2) onboard Akatsuki observed a remarkable cloud feature in the Venus' night-side disk, a sharp discontinuity of cloud opacity which subtends latitudinally to some thousands of km (Peralta et al., 2020).  Though obvious and seemingly common in the Venus' atmosphere as similar features can be identified in imagery since the beginning of the night-side observations (Allen and Crawford, 1984), the mechanism of this emormous cloud cover (ECC) has not yet been explained.

To characterize this ECC (aerosol size parameters and column numbers), we have analyzed the Akatsuki/IR2 data, as well as the Venus Express/VIRTIS-M data. Six sets of the Akatsuki/IR2 data (MM-DD = 03-27, 07-22, 08-09, 08-18, 08-27, and 09-06) are measurable with varying photometric uncertainties, due to contaminations from the intense day crescent. Seven VEx/VIRTIS data, as tabulated in Peralta et al. (2020), are also measured by the consistent method with that for IR2 data.
A reference region, which is just west of the discontinuity and is seemingly not affected by the ECC, is defined as the background cloud (BC) region. Radiances at the BC and the ECC regions are measured for two IR2 filter passbands (1.735 and 2.26 µm). They are plotted in the correlation plot (radiance at 2.26 µm in horizontal axis and radiance at 1.735 µm in vertical axis). The BC-to-ECC slope can be used to infer the aerosol size and abundance that changes the BC region to the ECC region.

Comparison of obtained characteristics of the ECC for different observing times will be presented and implication to the possible mechanism of this large-scale phenomenon will be discussed.

How to cite: Satoh, T., Sato, T., Horinouchi, T., Imamura, T., and Hashimoto, G.: A photometric study of the Enormous Cloud Cover seen in theVenus' night-side disk, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1054, https://doi.org/10.5194/epsc2022-1054, 2022.

We report on detection and upper-limit of H₂CO, O₃, NH₃, HCN, N₂O, NO₂, and HO₂ above the cloud deck using the SOIR instrument on-board Venus Express.

The SOIR instrument performs solar occultation measurements in the IR region (2.2 - 4.3 µm) at a resolution of 0.12 cm^-1, the highest of all instruments on board Venus Express. It combines an echelle spectrometer and an AOTF (Acousto-Optical Tunable Filter) for the order selection. SOIR performed more than 1500 solar occultation measurements leading to about two millions spectra.

The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus atmosphere at the terminator in the mesosphere, with an emphasis on vertical distribution of the gases.

In this work, we report detections in the mesosphere, between 60 and 100 km.

Implications for the mesospheric chemistry will also be addressed.

How to cite: Mahieux, A., Robert, S., Mills, F., Trompet, L., Aoki, S., Piccialli, A., Jessup, K. L., and Vandaele, A. C.: Minor species in the Venus mesosphere from SOIR on board Venus Express: detection and upper limit profiles of H2CO, O3, NH3, HCN, N2O, NO2, and HO2, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-921, https://doi.org/10.5194/epsc2022-921, 2022.

Observations of the Venus Climate Orbiter “Akatsuki” provide us with horizontal distributions of the horizontal winds derived from cloud tracking of the Ultraviolet Imager (UVI) and of temperature observed by the Longwave Infrared Camera (LIR). However, these observations are limited in altitude, local time (day or night side), and frequency. Then it is difficult to elucidate the general circulation of the Venus atmosphere, including various temporal and spatial scales, only from observations. In this study, we produced a Venus dataset (analysis) that has high temporal and spatial resolutions by assimilating horizontal winds derived by the Akatsuki observations. At the top of the cloud layer of Venus, there are planetary-scale atmospheric waves that are excited by the solar heating and move with the sun, called the thermal tides. In this presentation, we focused on thermal tides to verify the analysis.

We use the Venus atmospheric data assimilation system “ALEDAS-V" (Sugimoto et al., 2017) [1] for assimilation and the Venus atmospheric general circulation model “AFES-Venus" (Sugimoto et al., 2014) [2] for ensemble forecasts. AFES-Venus is a full nonlinear dynamical GCM on the assumption of hydrostatic balance, designed for the Venus atmosphere. ALEDAS-V uses the Local Ensemble Transform Kalman Filter, and is the first data assimilation system for the Venus atmosphere. We assimilated the cloud top (~70km) zonal and meridional winds obtained by tracking morphology, using Akatsuki UVI data (Horinouchi et al., 2021) [3] from September 1st to December 31st, 2018. The assimilation data (analysis) from October 1st to November 30th, 2018, is analyzed, because the root-mean-square-deviations (RMSD) from FR (free run; the case without data assimilation) are stable.

Figures (a) and (d) show the observed zonal and meridional winds, respectively. The zonal wind has a local minimum near 11 LT (local time) around the equator (Figure a). The meridional wind is the weakest at the equator and increases with latitude, and the amplitude is maximum around noon (Figure d) in the local time direction. Note that these winds obtained from observations exist only the dayside equatorward of 50° latitudes (Figure a and d).

Figures (b) and (e) show the deviations from the zonal means of zonal and meridional winds at an altitude of 70 km in the FR, respectively. For zonal wind, diurnal (zonal wavenumber 1) and semidiurnal (zonal wavenumber 2) tides are dominant at latitudes poleward and equatorward of 30, respectively (Figure b). The zonal wind deviation has a local minimum at 14-15LT, which is ~ 2 hours behind the observation (Figures a and b). The meridional wind deviation is polar and equatorial on the dayside and nightside, respectively (Figure e), and this distribution is consistent with Akatsuki's observation (Figure d).

Figures (c) and (f) show the zonal and meridional winds as a result of assimilation, respectively. The zonal wind in the equatorial region have a local minimum near 11 LT. The assimilation improved the semidiurnal tide closer to the observations (Figures a and c). The meridional wind is not so different from FR. This is probably because FR was originally very similar to observations (Figures d and f). These results are consistent with a previous study by Sugimoto et al. (2019) [4]. In addition, while the observed winds exist only on the dayside, the results of assimilation show that the horizontal winds field is modified significantly even on the nightside. It is suggested that spatially limited data assimilation can improve the general circulation of GCM.

In the future work, we are planning to release the assimilation dataset as the “objective analysis data” of Venus for the first time in the world.

[1] Sugimoto, N., et al. Development of an ensemble Kalman filter data assimilation system for the Venusian atmosphere. Scientific Reports 7(1), 9321 (2017).

[2] Sugimoto, N., et al. Baroclinic instability in the Venus atmosphere simulated by GCM. J. Geophys. Res. Planets 119, 1950–1968 (2014).

[3] Horinouchi, T., et al. Venus Climate Orbiter Akatsuki Cloud Motion Vector Data Set v1.0, JAXA Data Archives and Transmission System (2021).

[4] Sugimoto, N., et al. Impact of data assimilation on thermal tides in the case of Venus Express wind observation. Geophys. Res. Lett. 46, 4573–4580 (2019).

How to cite: Fujisawa, Y., Murakami, S., Sugimoto, N., Takagi, M., Imamura, T., Horinouchi, T., Hashimoto, G. L., Ishiwatari, M., Enomoto, T., Miyoshi, T., Kashimura, H., and Hayashi, Y.-Y.: Thermal tides reproduced in the assimilation results of horizontal winds obtained from Akatsuki UVI observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-309, https://doi.org/10.5194/epsc2022-309, 2022.

RIU-Planetary Reseach has won funding support for the reprocessing and the interpretation of the original raw open-loop occultation data taken by the Pioneer Venus Orbiter radio science experiment ORO from 1979 to 1988. These original raw open-loop data are available from the PDS while original processed atmospheric and ionospheric (temperature and electron density, respectively) profiles from the Venus atmosphere are not. 

We shall apply modern software code together with a new version of the Venus gravity field and newly processed orbit data available as SPICE kernels.

A review of the original data sets showed a variety of observation lengths ranging from a few minutes to about 20 minutes duration. The longer observation sets contain presumably ingress and egress data. We shall present atmospheric and ionospheric profiles processed from exemplary original Pioneer Venus Orbiter raw open-loop data setsand compare them with VEX VeRa radio occultation profiles for comparable observation conditions. 

How to cite: Pätzold, M., Hahn, M., Oschlisniok, J., Peter, K., and Tellmann, S.: Reprocessing Pioneer Venus Orbiter radio occultation data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1141, https://doi.org/10.5194/epsc2022-1141, 2022.

On August 10, 2021, the Mercury-bound BepiColombo spacecraft flew for the second time by Venus for a Gravitationally Assist Maneuver. During this second flyby of Venus, a limited number of instruments were turned on, allowing unique observations of the planet and its environment. Among these instruments, the Mass Spectrum Analyzer (MSA) that is part of the particle analyzer consortium onboard the magnetospheric orbiter (Mio) was able to acquire its first ion composition measurements in space. As a matter of fact, during a limited time interval upon approach of the planet, substantial ion populations were recorded by MSA, with characteristic energies ranging from about 20 eV up to a few hundreds of eVs. Most notably, comparison of the measured Time-Of-Flight spectra with calibration data reveals that these populations are of planetary origin, containing both Oxygen and Carbon ions. The Oxygen observations are to some extent consistent with previous in situ measurements from the ion mass composition sensor onboard Venus Express and Pioneer Venus Orbiter. As for Carbon, we report here the first ever in situ evidences of such an ion species in the near-Venus environment from around 6 planetary radii. Relative to the predominant O+, we show that the abundance of C+ is about ~30%. Furthermore, changes in the orientation of the magnetic field suggest that these planetary ions are located in the distant magnetosheath flank in the immediate vicinity of the bow-shock region.

How to cite: Hadid, L. and the MSA, MIA, MEA and MAG teams: Evidence of planetary carbon and oxygen ions in the outer flank of Venus magnetosheath, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-19, https://doi.org/10.5194/epsc2022-19, 2022.