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Venus/Titan‐type superrotation driven by stratospheric heating and intermittency seen in the superrotation dynamics are investigated using an idealized general circulation model in a high Rossby number regime (Ro = 7.5 to 23 for the strongest zonal jet) where the superrotation is formed by the meridional circulation and equatorward eddy momentum flux. When the jet core has a Rossby number of ∼23 on a slowly rotating or small planet, fast planetary‐scale Rossby waves are transiently amplified by both barotropic and baroclinic energy conversion and intermittently produce equatorward eddy momentum fluxes. At high latitudes, poleward eddy momentum transport also occurs when the poleward heat flux of baroclinic eddies is strong. On such a slowly rotating or small‐sized planet, equatorial superrotation is developed efficiently by weak, intermittent equatorward momentum flux in the presence of polar indirect circulation and the speed of the zonal flow is roughly constant over the low‐ and mid‐latitudes. In contrast, on a relatively fast rotating or large‐sized planet when the Rossby number is ∼7.5 for the jet core, although the zonal jets and equatorward eddy momentum fluxes intensify, equatorial superrotation is not developed efficiently (i.e., the superrotation intensity and its equatorial efficiency are small). Strong equatorward eddy momentum fluxes are produced continuously by slow barotropic Rossby waves on the equatorward flanks of the jets developed by the strong meridional circulation. The poleward heat fluxes of baroclinic waves are negligible because it is much smaller than the heat flux of the zonal‐mean meridional circulation. Plain Language Summary: Superrotation has been observed in planetary atmospheres and its dynamics have been investigated in previous studies. However, Venus/Titan‐type superrotation driven by stratospheric heating is not fully understood. The Venus/Titan‐type superrotation and intermittency of the dynamical process are elucidated using an idealized general circulation model with large Rossby numbers (Ro = 7.5 to 23) defined by the ratio of inertial force to Coriolis force. This work confirms that (i) the results are equivalent for the same Rossby number regardless of whether due to planetary rotation or size, and (ii) the superrotation mechanism caused by the meridional circulation and equatorward eddy momentum flux is a fundamental process commonly seen in the high Ro regime. Based on the sensitivity experiments with the planetary rotation or size altered, we discuss how the superrotation is maintained and compile its dynamics using the Rossby number. The superrotation is developed efficiently by weak, intermittent equatorward eddy momentum flux on a small‐sized or slowly rotating planet with a high Rossby number. In contrast, although zonal jets and continuous eddy momentum fluxes intensify on a relatively large‐sized or fast‐rotating planet with a relatively low Rossby number, the equatorial superrotation is not efficiently developed. Key Points: Rossby number dependence of Venus/Titan‐type superrotation and its related intermittency is elucidated using an idealized general circulation modelSuperrotation is developed efficiently by weak, intermittent equatorward eddy momentum flux for high Rossby numberEquatorial superrotation is not efficiently developed for low Rossby number, though zonal jets intensify at high latitudes [ABSTRACT FROM AUTHOR]

The concept of residence time of energy in a planetary atmosphere τ푅, recently introduced and computed for the Earth's atmosphere (Osácar et al., 2020), is here extended to the atmospheres of Venus, Mars and Titan. After a global thermal perturbation, τ푅is the time scale the atmosphere needs to return to equilibrium. The residence times of energy in the atmospheres of Venus, Earth, Mars and Titan have been computed. In the cases of Venus, Mars and Titan, these are mere lower bounds due to a lack of some energy data. [ABSTRACT FROM AUTHOR]

The abundance of SO dimers (SO)2 in the upper atmosphere of Venus and their implications for the enigmatic ultraviolet absorption has been investigated in several studies over the past few years. However, the photochemistry of sulfur species in the upper atmosphere of Venus is still not well understood and the identity of the missing ultraviolet absorber(s) remains unknown. Here we update an existing photochemical model of Venus' upper atmosphere by including the photochemistry of SO dimers. Although the spectral absorption profile of SO dimers fits the unknown absorber, their abundance is found to be too low for them to contribute significantly to the absorption. It is more likely that their photolysis and/or reaction products could contribute more substantively. Reactions of SO dimers are found to be important sources of S2O, and possibly higher order SnO species and polysulfur, Sn. All of these species absorb in the critical ultraviolet region and are expected to be found in both the aerosol and gas phase. indicating that in-situ high resolution aerosol mass spectrometry might be a useful technique for identifying the ultraviolet absorber on Venus. Photochemistry of sulfur species in the upper Venus atmosphere is not well understood and the identity of ultraviolet (UV) absorber(s) remain unknown. Here, the authors show that sulfur monoxide dimer chemistry is a possible source of polysulfur, which could be responsible for the UV absorption. [ABSTRACT FROM AUTHOR]

Utilizing the in situ observations of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) and the magnetometer (MAG) onboard Venus Express, we report evidence of crossing the ion diffusion region of magnetic reconnection. Evidence of magnetic reconnection is based on two cases recorded by Venus Express in the Venusian magnetotail. In both cases, the variations of the magnetic field components are consistent with the classical picture of crossing the ion diffusion region. Our evidence is also supported by observed ion flows whose directions and speeds agree with expected characteristics of reconnection outflow. The reconnection crossing cases demonstrate that magnetic reconnection can appear in both ± E-hemispheres in the Venusian magnetotail. The Venusian magnetotail provides a unique space laboratory for the investigation of the reconnection process. Plain Language Summary Magnetic reconnection is known as an important process that transforms magnetic energy into the kinetic and thermal energy of plasma, and has been frequently observed in the Earth's magnetosphere. In contrast to Earth, Venus lacks an intrinsic magnetic field and magnetic reconnection in the space environment of Venus has been less investigated. A previous study by T. L. Zhang et al. (2012, https://doi.org/10.1126/science.1217013) demonstrated that magnetic reconnection can occur in the Venusian magnetotail. However, in situ observation of the ion diffusion region has not yet been reported. With a comprehensive survey of the plasma and magnetic field measurements of Venus Express, we report the first in situ evidence of crossing the ion diffusion region in the Venusian magnetotail. Our results confirm the existence of reconnection in the Venusian magnetotail and suggest that magnetic reconnection could play an important role in the plasma dynamics of the Venusian magnetotail. [ABSTRACT FROM AUTHOR]

This work examines the planetary wave-induced variability within the upper mesosphere/lower thermosphere of Venus by utilizing the Venus Thermospheric General Circulation Model (VTGCM). Rossby and Kelvin wave perturbations are driven by variations in the geopotential height of the VTGCM lower boundary (~70 km). A suite of simulations was conducted to examine the impact of the individual and combined waves propagating from two different lower boundary conditions (uniform and varying). The Kelvin wave is the more dominant wave which produces the most variability. The combination of the Kelvin and Rossby waves provides a maximum temperature amplitude of 13 K at 92 km and maximum zonal wind amplitude of 23 m/s at 102 km. The combined waves overall are able to propagate up to 125 km. Most of the variation within the temperature, winds, and composition occurs between 70 and 110 km. The varying lower boundary increases the magnitude of the wave deposition and atmospheric responses, but weakly changes the propagation altitude. The thermal variation due to the planetary waves does not reproduce most observed variations. The simulated O2 IR nightglow emission is sensitive to the waves with respect to intensity and local time, but lacks latitudinal variation. The integrated intensity ranges from 1.2 MR to 1.65 MR and the local time ranges from 0.33 local time to 23.6 local time. Overall, planetary waves do affect the atmospheric structure, but there are still large observed variations that planetary waves alone cannot explain (i.e., thermal structure). [ABSTRACT FROM AUTHOR]

Positive streamer discharges have been studied and modelled extensively in air. Here we study positive streamers in CO2 with and without oxygen admixtures; they are relevant for current high voltage technology as well as for discharges in the atmosphere of Venus. We discuss that no efficient photoionization mechanism is known for gases with a large CO2 fraction, as photons in the relevant energy range are rapidly absorbed. Hence positive streamers can propagate only due to some other source of free electrons ahead of the ionization front. Therefore we study positive streamer propagation in CO2 with different levels of background ionization to provide these free electrons. The effect of replacing photoionization by background ionization is studied with simulations in air. Simulating streamers in background fields of 16 to 20 kV cm−1 at standard temperature and pressure within a gap of 6.4 cm, we find that streamer propagation is rather insensitive to the level of photoionization or background ionization. We also discuss that the results depend not only on the value of breakdown field and applied electric field, and on preionization or photoionization, but also on the electron mobility μ(E) and the effective ionization coefficient αeff(E), that are gas-dependent functions of the electron energy or the electric field. [ABSTRACT FROM AUTHOR]

A new method of calculation of equilibrium compositions of single-phase multicomponent systems in a wide range of temperatures, pressures, and elemental compositions is proposed. It is based on the minimization of the integral characteristic of the slope of the thermodynamic potential surface in the space of coordinates of chemical reactions. The proposed algorithm is applied to the definition of area of the thermodynamic stability of freons in volcanic gases and to the construction of the equilibrium profiles of the height distribution of sulphur-containing components of Venusian atmosphere. A new method of calculation of equilibrium compositions of single-phase multicomponent systems in a wide range of temperatures, pressures, and elemental compositions is proposed. The proposed algorithm is applied to the definition of area of the thermodynamic stability of freons in volcanic gases and to the construction of the equilibrium profiles of the height distribution of sulphur-containing components of Venusian atmosphere. [ABSTRACT FROM AUTHOR]

The article presents aspects of the use of inflatable decelerators in the design of spacecraft (SC) intended for the study of the atmosphere of Venus. The results of the aerothermodynamics calculations and justification of the thermal protection of SC with decelerators are given. Their advantages over conventional descent modules during aerodynamic deceleration in the planet's atmosphere are shown. [ABSTRACT FROM AUTHOR]

Superrotation is a dynamical regime where the atmosphere circulates around the planet in the direction of planetary rotation with excess angular momentum in the equatorial region. Superrotation is known to exist in the atmospheres of Venus, Titan, Jupiter, and Saturn in the solar system. Some of the exoplanets also exhibit superrotation. Our understanding of superrotation in a framework of circulation regimes of the atmospheres of terrestrial planets is in progress thanks to the development of numerical models; a global instability involving planetary-scale waves seems to play a key role, and the dynamical state depends on the Rossby number, a measure of the relative importance of the inertial and Coriolis forces, and the thermal inertia of the atmosphere. Recent general circulation models of Venus's and Titan's atmospheres demonstrated the importance of horizontal waves in the angular momentum transport in these atmospheres and also an additional contribution of thermal tides in Venus's atmosphere. The atmospheres of Jupiter and Saturn also exhibit strong superrotation. Recent gravity data suggests that these superrotational flows extend deep into the planet, yet currently no single mechanism has been identified as driving this superrotation. Moreover, atmospheric circulation models of tidally locked, strongly irradiated exoplanets have long predicted the existence of equatorial superrotation in their atmospheres, which has been attributed to the result of the strong day-night thermal forcing. As predicted, recent Doppler observations and infrared phase curves of hot Jupiters appear to confirm the presence of superrotation on these objects. [ABSTRACT FROM AUTHOR]

Low lunar gravity is not able to hold much atmosphere presumably created by degassing its solid body. Not like massive rocky planets-Venus, Earth, and Mars. They have atmospheres with their masses roughly proportional to their orbital frequencies (more frequency-more expelled volatiles from the planets depths by systematic wave shaking). Nevertheless, very thin exosphere is observed around the Moon. Its origin is related to the solar wind destructive action in the very thin surface film, meteorite impacts and, likely, due to constant trembling in the microwave diapason (modulated diapason due to the Moon orbiting around Earth and in Galaxy). By various methods in the lunar exosphere are found Argon 20000-100000 atoms in cm3, helium 500-30000, neon up to 20000; sodium 70, potassium 17, hydrogen fever than 17 atoms in cm3; methane and carbon also were found. There is a kind of equilibrium between supply of atoms from the solid lunar body and expelling them to space. Another result of constant trembling is in regolith layering. [ABSTRACT FROM AUTHOR]

Venus is an exceptional natural experiment to test our understanding of atmospheric sulfur chemistry. Previous modeling efforts have focused on understanding either the middle or lower atmosphere. In this work, we performed the first full atmosphere analysis of the chemical transport processes on Venus from the surface to 110 km using a 1‐D diffusion model with photochemistry. We focused on the cycling of chemical species between the upper and lower atmospheres and interactions between distinct species groups including SO x, CO x + OCS, chlorides, NO x, O x, and S x. We tested different eddy diffusivity profiles and investigated their influences on the vertical profiles of important species. We find that the assumed boundary conditions in previous models strongly impacted their simulation results. This has a particularly large effect for SO 2. We find the high SO 2 abundance in the lower atmosphere is readily transported into the middle atmosphere, far exceeding observed values. This implies some yet unknown chemistry or process limiting SO 2 mixing. We summarize outstanding questions raised by this work and note chemical reactions that should be the highest priority for future laboratory studies and ab initio calculations. Plain Language Summary: Venus's atmosphere can be broadly separated into lower and middle regions, separated by a thick cloud deck. Chemistry in the lower atmosphere is controlled by the high temperatures below the clouds. In the middle atmosphere, photochemistry stimulated by solar UV radiation is dominant. Previous works have modeled either the lower or middle atmosphere to understand these chemical processes. In this work, we create a single model that encompasses both regions to understand how chemical species are cycled. We find that the large abundance of SO 2 in the lower atmosphere is transported into the middle atmosphere, far exceeding what is observed. We argue that this suggests some as of yet unknown chemistry or process that is limiting the SO 2 flux from the lower atmosphere. Key Points: We perform the first thorough analysis of a Venus atmospheric chemistry model that extends from the surface to 110 kmSome previously proposed chemical pathways break down when more complete chemistry is usedTo match observed abundances SO 2 must be inhibited from diffusing through the clouds by some unknown process [ABSTRACT FROM AUTHOR]

We present the results of our numerical simulations of the general circulation in the atmosphere of a hypothetical super-Earth within a model based on the solution of the complete system of hydrodynamic equations. The MIPT/PGI GCM model used for our computations has already been successfully adopted to describe the general circulation of the atmosphere of Venus. The model features high resolution and the absence of linear viscosity. The atmospheric gas is a mixture of gases in some constant proportion and the influence of the aerosol component on the equation of state may be neglected. The Newtonian relaxation scheme is used to describe the processes related to heat transfer. We have found that the westerly zonal superrotation, which can manifest itself in the form of equatorial and two mid-latitude jets, is the main mechanism of circulation in the atmosphere. The positions and intensities of the mid-latitude jets are largely determined by the molecular weight of the atmosphere and the equator–pole temperature contrast. We show the trends reflecting these changes. In the case of a tidally locked super-Earth we also detect a stable equatorial jet perturbed by a Kelvin wave. The intensity of the perturbations has been found to increase with decreasing molecular weight of the atmosphere. We perform our simulations in the framework of a simple greenhouse model. [ABSTRACT FROM AUTHOR]

Venus is Earth's closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth's sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years. The oxygen isotope composition of Venus is currently unknown. However, this single measurement ( Δ 17 O ) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ 17 O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide. Determining the Δ 17 O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ 17 O , this would favour the classic, lower energy, giant impact scenario. We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered. Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a "Grab and Go" strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, "vacuum-cleaner" device) to ensure success. Surface operations would take no longer than one hour. Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth's planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems. [ABSTRACT FROM AUTHOR]

Low‐intensity high‐temperature (LIHT) solar cells are needed for extended photovoltaic power generation in both the lower atmosphere as well as at the surface of Venus. Double‐junction GaInP/GaAs solar cells that may be able to operate and survive, with suitable encapsulation, for several weeks on the 465°C Venus surface have been developed. These solar cells have been optimized for operation under the Venus solar spectrum, which is different from that of the Earth. [ABSTRACT FROM AUTHOR]

We mapped the distribution of the 365‐nm albedo of the Venus atmosphere over the years 2006–2014, using images acquired by the Venus Monitoring Camera (VMC) on board Venus Express. We selected all images with a global view of Venus to investigate how the albedo depends on longitude. Bertaux et al. (2016, https://doi.org/10.1002/2015JE004958) reported a peak in albedo around 100° longitude and speculated on an association with the Aphrodite Terra mountains. We show that this peak is most likely an artifact, resulting from long‐term albedo variations coupled with considerable temporal gaps in data sampling over longitude. We also used a subset of images to investigate how the albedo depends on local time, selecting only south pole viewing images of the dayside (local times 7–17 hr). Akatsuki observed mountain‐induced waves in the late afternoon at 283 nm and 10 μm (Fukuhara et al., 2017, https://doi.org/10.1038/ngeo2873). We expect that the presence of such waves may introduce 365‐nm albedo variations with a periodicity of one solar day (116.75 Earth days). We searched for such a periodicity peak at 15:30–16:00 local time and low latitudes but did not find it. In conclusion, we find that temporal albedo variations, both short and long term, dominate any systematic variations with longitude and local time. The nature of VMC dayside observations limits regular data sampling along longitudes, so longitudinal variations, if they exist, are difficult to extract. We conclude that any influence by the Venus surface on 365‐nm albedo is negligible within this data set. Plain Language Summary: Recently, it was reported that mountains on the surface of Venus can affect the atmosphere at the altitude of the cloud tops (70 km). For example, the brightness of the clouds (albedo) in images made by the Venus Express spacecraft at ultraviolet wavelengths (365 nm) was suspected to peak over a high mountain, Aphrodite Terra. We searched for such surface effects using the Venus Express images taken at 365 nm over the years 2006–2014. We found that the albedo was strongly variable over this period and that different longitudes were systematically imaged at different times. It is therefore not possible to uncover the influence of mountains on the albedo, and we believe that the reported albedo peak near Aphrodite Terra is most likely not real. Another spacecraft, Akatsuki, observed global‐scale atmospheric waves in the late afternoon that are originated by mountains. We also searched for albedo changes at the same latitude with a period of one solar day (116.75 Earth days) that might be linked with these atmospheric waves but did not find any period above the noise level. We conclude that the influence of mountains on the 365‐nm albedo is too weak to be recognized in Venus Express images. Key Points: Temporal variations of the 365‐nm albedo of Venus dominate over any systematic variations along longitude or over local timeWe found no systematic influence by mountains on the 365‐nm albedo distribution, in contrast to a previous report [ABSTRACT FROM AUTHOR]

One popular view of Venus' climate history describes a world that has spent much of its life with surface liquid water, plate tectonics, and a stable temperate climate. Part of the basis for this optimistic scenario is the high deuterium to hydrogen ratio from the Pioneer Venus mission that was interpreted to imply Venus had a shallow ocean's worth of water throughout much of its history. Another view is that Venus had a long‐lived (∼100 million years) primordial magma ocean with a CO2 and steam atmosphere. Venus' long‐lived steam atmosphere would sufficient time to dissociate most of the water vapor, allow significant hydrogen escape, and oxidize the magma ocean. A third scenario is that Venus had surface water and habitable conditions early in its history for a short period of time (<1 Gyr), but that a moist/runaway greenhouse took effect because of a gradually warming Sun, leaving the planet desiccated ever since. Using a general circulation model, we demonstrate the viability of the first scenario using the few observational constraints available. We further speculate that large igneous provinces and the global resurfacing hundreds of millions of years ago played key roles in ending the clement period in its history and presenting the Venus we see today. The results have implications for what astronomers term "the habitable zone," and if Venus‐like exoplanets exist with clement conditions akin to modern Earth, we propose to place them in what we term the "optimistic Venus zone." Plain Language Summary: We have little data on our neighbor Venus to help us understand its climate history. Yet Earth and Venus are sister worlds: They initially formed close to one another and have nearly the same mass and radius. Despite the differences in their current atmospheres and surface temperatures, they likely have similar bulk compositions, making comparison between them extremely valuable for illuminating their distinct climate histories. We analyze our present data on Venus alongside knowledge about Earth's climate history to make a number of exciting claims. Evaluating several snapshots in time over the past 4+ billion years, we show that Venus could have sustained liquid water and moderate temperatures for most of this period. Cloud feedbacks from a slowly rotating world with surface liquid water reservoirs were the keys to keeping the planet clement. Contrast this with its current surface temperature of 450° and an atmosphere dominated by carbon dioxide and nitrogen. Our results demonstrate that it was not the gradual warming of the Sun over the eons that contributed to Venus present hothouse state. Rather, we speculate that large igneous provinces and the global resurfacing hundreds of millions of years ago played key roles in ending the clement period in its history. Key Points: Venus could have had habitable conditions for nearly 3 billion yearsSurface liquid water is required for any habitable scenarioSolar insolation through time is not a crucial factor if a carbonate‐silicate cycle is in action [ABSTRACT FROM AUTHOR]

The present atmosphere of Venus contains almost no water, but recent measurements indicate that in its early history, Venus had an Earth‐like ocean. Understanding how the Venusian atmosphere evolved is important not only for Venus itself but also for understanding the evolution of other planetary atmospheres. In this study, we quantify the escape rates of oxygen ions from the present Venus to infer the past of the Venusian atmosphere. We show that an extrapolation of the current escape rates back in time leads to the total escape of 0.02–0.6 m of a global equivalent layer of water. This implies that the loss of ions to space, inferred from the present state, cannot account for the loss of an historical Earth‐like ocean. We find that the O+ escape rate increases with solar wind energy flux, where more energy available leads to a higher escape rate. Oppositely, the escape rate decreases slightly with increased extreme ultraviolet radiation (EUV) flux, though the small variation of EUV flux over the measured solar cycle may explain the weak dependency. These results indicate that there is not enough energy transferred from the solar wind to Venus' upper atmosphere that can lead to the escape of the atmosphere over the past 3.9 billion years. This means that the Venusian atmosphere did not have as much water in its atmosphere as previously assumed or the present‐day escape rates do not represent the historical escape rates at Venus. Otherwise, some other mechanisms have acted to more effectively remove the water from the Venusian atmosphere. Plain Language Summary: Today, Venus only has small amounts of water in its atmosphere. In its early history, Venus presumably contained an Earth‐like ocean of several meters. The evolution of the atmosphere may have been caused by escape of atmospheric content to space. In this study, we investigate how much the escape of oxygen ions to space could have affected the atmospheric evolution for Venus from measurements of the present‐day escape rates. Using measurements of oxygen ions in the vicinity of Venus, we show that the amount of energy available in the solar wind to be transferred to the upper atmosphere of Venus determines how much of the atmosphere escapes. From the evolution of the energy in the solar wind over the past 3.9 billion years, together with the relation between the solar wind energy and oxygen ion escape, we show that in total, about 0.02–0.6 m of water depth, if spread equally over the entire Venusian surface, was lost. This indicates that either Venus did not have as much water as previously assumed or the current escape rates are not representative of the historical escape rates. Otherwise, some other mechanisms must have acted to more effectively remove the water from Venus. Key Points: The current escape of O+ from Venus is energy limited not source limitedThe extrapolated mass loss through ion escape accounts for 6 mbar of the current Venusian atmosphereThe total mass loss from ion escape cannot account for the loss of a large water inventory at Venus [ABSTRACT FROM AUTHOR]

The vertical coupling between the cloud‐level atmosphere and the thermosphere of Venus was investigated using 365 nm images obtained by the Ultraviolet Imager on board Akatsuki and oxygen atom 135.6 nm dayglow intensities obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics on board the space telescope Hisaki. Simultaneous observations revealed a common periodicity of ~3.6 Earth days in the cloud‐tracked velocity, the cloud brightness, and the airglow intensity. The oscillation at the cloud level is attributed to a planetary‐scale Kelvin wave. A one‐dimensional linear wave model showed that the Kelvin wave cannot propagate from the cloud level to the thermosphere because of radiative damping. The modeling also revealed that a small‐scale gravity waves having wavelengths of <1,000 km can reach the thermosphere on the dawnside and that they are strongly attenuated on the duskside because of the difference in the background winds with vertical shears. We further developed a one‐dimensional photochemical model to investigate the response of the airglow intensity to the change of the eddy diffusion coefficient, which is expected to increase with the wave amplitude. The model showed that a 3.6‐day oscillation of the diffusion coefficient with an amplitude of ~300 m2 s−1 explains the observed airglow intensity variation. A possible cause of the 3.6‐day period is the filtering of gravity wave fluxes by the Kelvin wave‐induced wind. Plain Language Summary: The circulation of the thermosphere of Venus is thought to be strongly affected by momentum transport from the lower atmosphere associated with atmospheric waves; the wind speed observed in the thermosphere was slower than that calculated in numerical models. However, there have been no evidence for such vertical propagation of waves from lower atmosphere through the thermosphere. In this study, the interaction between the cloud‐level atmosphere and the thermosphere of Venus was investigated by simultaneous observations using the Venus orbiter Akatsuki and the Earth‐orbiting space telescope Hisaki. We have identified the same periodicity of ~3.6 Earth days in the cloud‐top wind and the thermospheric airglow emission. Simplified models demonstrated that small‐scale gravity waves can propagate to the thermosphere and that the modulation of gravity wave fluxes by a Kelvin wave might explain the observed periodicity common to the two altitude regions. These results suggest that the gravity waves are responsible for the vertical coupling between cloud‐level atmosphere and the thermosphere. Key Points: Simultaneous observations by a Venus orbiter and an Earth‐orbiting space telescope were conducted in June 2017A common periodicity in the cloud‐level atmosphere and the thermosphere was detectedModel calculations showed that the thermospheric periodicity can be attributed to vertical propagation of small‐scale gravity waves [ABSTRACT FROM AUTHOR]

Spectroscopic solar occultation measurements by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus/Solar Occultation at Infrared instrument (SPICAV/SOIR) onboard the Venus Express orbiter gave new data about upper haze aerosol properties, its vertical distribution and spatial and temporal variations. Early study with three channels of SPICAV/SOIR instrument using a few selected orbits indicated presence of two aerosol modes in particle size distribution (Wilquet et al., 2009). Analysis of aerosol properties from the SPICAV−IR spectrometer for the whole Venus Express data set obtained from May 2006 till November 2014 has proved it for some occultations (Luginin et al., 2016). In this work, we report retrieval of the upper haze (81–100 km) aerosol properties from 101 simultaneous SPICAV−UV and –IR solar occultation sessions acquired between March 2007 and January 2013. A joint analysis of the data from two spectrometers allowed us to characterize the size distribution ∼10 km higher in the atmosphere compared to previous analysis and to detect bimodal distribution in ∼50% of observations previously believed to be unimodal. At altitudes 81–92 km bimodality is observed in >50% of cases. Mode 2 particles are detected up to 98 km and mode 1 up to 100 km. Mean radius equals 0.14 ± 0.03 μm for mode 1 and 0.78 ± 0.18 μ m for mode 2. Number density profiles for both modes of particles exponentially decrease with altitude, starting from 50 cm−3 and 0.3 cm−3 at 82 km for mode 1 and mode 2, respectively, and reaching 3 cm−3 at 98 km for mode 1 and 0.03 cm−3 at 94 km for mode 2. • At altitudes 81–92 km bimodal distribution was observed in >50% of observations. • The mean effective radii are 0.14 ± 0.03 μm for mode 1 and 0.78 ± 0.18 μm for mode 2. • Number density profiles for both modes exponentially decrease with altitude. • Effective variance of mode 1 reaches 0.4 at <84 km and 0.03–0.15 at higher altitudes. • Effective variance of mode 2 is almost constant with height with mean value 0.04 ± 0.02. [ABSTRACT FROM AUTHOR]

This study investigates the impact of model input parameters on the characteristic features of the dayside V 2 layer in the Venus ionosphere using an in-house developed one-dimensional photochemical model (1D-PCM) and observations from Venus Express radio science experiments (VeRa). 1D-PCM is simulated for different combinations of neutral density models (VTS3, a global empirical model of the Venus Thermosphere, and VenusGRAM, the Venus Global Reference Atmospheric Model), solar flux models (Solar 2000 (S2K), and observations by SEE (Solar EUV Experiment) onboard the NASA's TIMED, the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics, satellite). The hmV 2 (height of the V 2 layer plasma density) is found to be better reproduced in VTS3-SEE and VTS3-S2K pairs of combination, indicating that VTS3 is a more representative model for Venusian neutral density. The nmV 2 (peak plasma density of the V 2 layer) remains consistently higher when using SEE data for solar fluxes, but the model deviates significantly for Solar Zenith Angles (SZA) between 65 ∘ and 85 ∘ , possibly due to differences in neutral density at high SZA where the temperature is lower than predicted by the neutral density model. Quantitative analysis reveals that errors in the 1D-PCM, with deviations of 1 to 2 km in hmV 2 and 5%–10% difference in nmV 2 between the model and observations, could be due to uncertainties in the neutral density and solar flux models. Comparison with the Transplanet model suggests that accounting for input uncertainties can improve the model's ability to reproduce observations. This study provides insights into the influence of input parameters on the Venus ionosphere and highlights the importance of considering uncertainties in modeling studies. • The electron density profiles are derived from the frequency residuals of VeRa observations. • The 1D-PCM reproduces features of the V 2 within the uncertainty limit. • The deviation between the observation and the model is maximum at large solar zenith angles. • The VTS3 neutral density model is a better representative of the Venusian atmosphere. [ABSTRACT FROM AUTHOR]

The magnetized supersonic solar wind, when flowing around planets, forms a magnetic barrier near the streamlined surface. The main feature of the magnetic barrier is that the magnetic pressure prevails over the plasma pressure. The Hall-MHD model is used to simulate the magnetic barrier in the case of solar wind flow around the atmosphere of Venus. The obtained numerical results are compared with an analytical approximation of the magnetic barrier thickness, which expresses the dependence of the magnetic barrier on solar wind parameters. Particular attention is paid to the physical reasons for the asymmetry of the magnetic barrier caused by the Hall effects, which are mainly concentrated in the boundary layer near the ionopause, where the electric current has a maximum strength. An additional source of asymmetry is also considered, which acts in the same direction and is associated with the influence of the normal component of the electric field on the specific behavior of new atmospheric ions. It is shown that solar wind protons are loaded by new atmospheric ions mainly in the E + hemisphere. In the case of more intense loading, the boundary of the magnetic barrier and the shock wave are located farther from the ionopause. • Hall-MHD effects cause a strong magnetic field asymmetry near the Venus ionopause. • Hall-related changes in magnetic and plasma pressures are opposite to each other. • Asymmetry due to Hall effects near Venus increases as solar wind density decreases. • The finite Larmor radius of ions causes an asymmetry additional to the Hall effect. [ABSTRACT FROM AUTHOR]

The CO2(010)–O(3P) vibrational energy transfer (VET) efficiency is a key input to aeronomical models of the energy budget of the upper atmospheres of Earth, Venus, and Mars. This work addresses the physical mechanisms responsible for the high efficiency of the VET process at the thermal energies existing in the terrestrial upper atmosphere (150 K≤=T≤=550 K). We present a quantum-mechanical study of the process within a reduced-dimensionality approach. In this model, all the particles remain along a plane and the O(3P) atom collides along the C2v symmetry axis of CO2, which can present bending oscillations around the linear arrangement, while the stretching C–O coordinates are kept fixed at their equilibrium values. Two kinds of scattering calculations are performed on high-quality ab initio potential energy surfaces (PESs). In the first approach, the calculations are carried out separately for each one of the three PESs correlating to O(3P). In the second approach, nonadiabatic effects induced by spin-orbit couplings (SOC) are also accounted for. The results presented here provide an explanation to some of the questions raised by the experiments and aeronomical observations. At thermal energies, nonadiabatic transitions induced by SOC play a key role in causing large VET efficiencies, the process being highly sensitive to the initial fine-structure level of oxygen. At higher energies, the two above-mentioned approaches tend to coincide towards an impulsive Landau-Teller mechanism of the vibrational to translational (V-T) energy transfer. [ABSTRACT FROM AUTHOR]

Seismology on Venus has long eluded planetary scientists due to extreme temperature and pressure conditions on its surface, which most electronics cannot withstand for mission durations required for ground-based seismic studies. We show that infrasonic (low-frequency) pressure fluctuations, generated as a result of ground motion, produced by an artificial seismic source known as a seismic hammer, and recorded using sensitive microbarometers deployed on a tethered balloon, are able to replicate the frequency content of ground motion. We also show that weak, artificial seismic activity thus produced may be geolocated by using multiple airborne barometers. The success of this technique paves the way for balloon-based aero-seismology, leading to a potentially revolutionary method to perform seismic studies from a remote airborne station on the earth and solar system objects with substantial atmospheres such as Venus and Titan. [ABSTRACT FROM AUTHOR]

Longwave Infrared Camera (LIR) on board Akatsuki first revealed the global structure of the thermal tides in the upper cloud layer of Venus. The data were acquired over three Venusian years, and the analysis was done over the areas from the equator to the midlatitudes in both hemispheres and over the whole local time. Thermal tides at two vertical levels were analyzed by comparing data at two different emission angles. Dynamical wave modes consisting of tides were identified; the diurnal tide consisted mainly of Rossby‐wave and gravity‐wave modes, while the semidiurnal tide predominantly consisted of a gravity‐wave mode. The revealed vertical structures were roughly consistent with the above wave modes, but some discrepancy remained if the waves were supposed to be monochromatic. In turn, the heating profile that excites the tidal waves can be constrained to match this discrepancy, which would greatly advance the understanding of the Venusian atmosphere. Plain Language Summary: On Venus, the atmosphere circulates 60 times faster than the solid body of Venus; this phenomenon is called "superrotation," and it is one of the mysteries of the Venusian atmosphere. To maintain the fast circulation, thermal tides, which are global‐scale atmospheric waves excited by solar heating, have been considered a very important candidate because they have the ability of accelerating the atmosphere through propagating. A midinfrared camera onboard the Japanese Venus orbiter, Akatsuki, can capture temperature perturbations due to the thermal tides in the upper cloud level (60‐ to 70‐km altitude), and it revealed their global and vertical structures with a long‐term observation (more than three Venusian years) for the first time. Interestingly, we found that the location of the maximum temperature at the cloud top level was different from noon where solar energy input is at a maximum. In addition, the location was shifted toward the morning side as the sensing altitude increased. This finding is an evidence of the vertical traveling of the thermal tides, indicating the wave's atmospheric acceleration. Key Points: Akatsuki/LIR revealed the global structures of thermal tides across the equator in the upper cloud layer of Venus for the first timeUsing the emission angle dependence of LIR's sensing altitude, upward propagation of the semidiurnal tide was confirmedWave types consisting of the thermal tides were identified [ABSTRACT FROM AUTHOR]

The current goals of the astrobiology community are focused on developing a framework for the detection of biosignatures, or evidence thereof, on objects inside and outside of our solar system. A fundamental aspect of understanding the limits of habitable environments (surface liquid water) and detectable signatures thereof is the study of where the boundaries of such environments can occur. Such studies provide the basis for understanding how a once inhabitable planet might come to be uninhabitable. The archetype of such a planet is arguably Earth's sibling planet, Venus. Given the need to define the conditions that can rule out bio-related signatures of exoplanets, Venus provides a unique opportunity to explore the processes that led to a completely uninhabitable environment by our current definition of the term. Here we review the current state of knowledge regarding Venus, particularly in the context of remote-sensing techniques that are being or will be employed in the search for and characterization of exoplanets. We discuss candidate Venus analogs identified by the Kepler and TESS exoplanet missions and provide an update to exoplanet demographics that can be placed in the potential runaway greenhouse regime where Venus analogs are thought to reside. We list several major outstanding questions regarding the Venus environment and the relevance of those questions to understanding the atmospheres and interior structure of exoplanets. Finally, we outline the path toward a deeper analysis of our sibling planet and the synergy to exoplanetary science. [ABSTRACT FROM AUTHOR]

Balloon systems show great promise for exploring the atmospheres of extra-terrestrial bodies in the solar system. The balloon system concept was demonstrated by the aerostats aboard the Vega 1 and 2 missions sent to Venus. Such systems glean propulsion from atmospheric winds, and at present are unable to travel in a direction perpendicular to the direction of the wind, limiting their exploration potential. A control system capable of modifying the system trajectory by traveling in a direction perpendicular to the direction of the wind is desired to increase exploration potential as well as to perform tasks such as maintaining latitude. A balloon and sail system which can use wind velocity and density gradients to produce a guiding force perpendicular to the velocity of the wind is discussed here. Such a guidance system is passive in nature and requires little power for actuation and control. It was previously demonstrated that such a control system is capable of generating guiding velocities of several meters per second within the Venusian atmosphere. Furthermore, this control system was shown to be capable of achieving sufficient control for the majority of the latitudes on Venus. This work builds on previous results and demonstrates the benefits of being able to generate guiding velocities via a sail system by viewing the trajectories taken by planetary balloon systems employing such a system. First, a description of the system model is given. Next, for the atmospheres of Venus and Titan, trajectory control is demonstrated for various sail parameters, such as sail size and mass. The benefit of such control is shown by the ability to achieve various latitudes of interest for a given flight duration. These latitudes are chosen based on geographic features, such as lakes on Titan. Finally, a PI controller is added to the model to demonstrate rudimentary control of the balloon system for maintaining and changing latitudes. A brief discussion regarding the control law of the system is also provided. • Tether and sail guidance systems can provide latitude control for balloon missions. • The equilibrium model must be solved while solving for balloon system trajectories. • Meridional winds can be overcome by increasing tether length and sail mass. • Sail attitude and lift coefficient saturation limit the influence of the sail. [ABSTRACT FROM AUTHOR]

The Venus atmosphere is of significant interest yet only rudimentary solid data have been gathered about its composition and chemistry. These measurements are scattered through time and place and are limited by parameters such as resolution and error margins as well as reinterpretations. This paper presents an extensive compilation of published in situ data for the atmospheric composition of Venus. It also includes remotely gathered measurements and some extrapolated and modeled data for the lower atmosphere. The composition tables are divided in four categories: noble gases, reactive gases, noble, and nonnoble isotopes. These tables were first presented in 2016 within the scientific heritage appendix of the Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission proposal. These tables provide respective measurements, error margins, techniques, altitudes, instruments, mission, and references. The objective of this paper is to provide a simple, comprehensive list of available measurements to date, in particular the in situ data, to serve as a quick overall Venus atmosphere data reference. Key Points: This paper presents tables that provide a comprehensive listing of Venus atmospheric dataThe data covers measurements gathered in situ in the Venus atmosphereA discussion of measurement definition is provided for data clarity [ABSTRACT FROM AUTHOR]

We explore the dominant modes of variability in the observed albedo at the cloud tops of Venus using Akatsuki UVI 283 nm and 365 nm observations, which are sensitive to SO2 and unknown UV absorber distributions respectively. The observations, taken over the period Dec. 2016 to May 2018, consist of images of the dayside of Venus, most often observed at intervals of two hours, but interspersed with longer gaps. The orbit of the spacecraft does not allow for continuous observation of the full dayside and the unobserved regions cause significant gaps in the datasets. Each dataset is subdivided into three subsets for three observing periods, the unobserved data are interpolated, and each subset is then subjected to a principal component analysis to find six oscillating patterns in the albedo. Principal components in all three periods show similar morphologies at 283 nm, but are much more variable at 365 nm. Some spatial patterns and the timescales of these modes correspond to well-known physical processes in the atmosphere of Venus such as the ~4-day Kelvin wave, 5-day Rossby waves, and the overturning circulation, while others defy a simple explanation. We also a find a hemispheric mode that is not well understood and discuss its implications. [ABSTRACT FROM AUTHOR]

Venus is the closest and most similar planet to Earth in the whole solar system, yet, basic measurements are missing. The atmospheric composition has been studied to some extent with the Pioneer Venus Orbiter mission and the more recent Venus Express, however, the concentration of many species and their isotopic ratios are not yet known with satisfying accuracy. Especially when it comes to the heavy noble gases as Kr and Xe, there is little to no collected data in this field. These elements form a key link to the reconstruction of the atmospheric evolution, which would deliver crucial information on the formation of Earth-like bodies. Knowing the abundances of the noble gases may allow us to answer the question why Venus did not evolve to a potentially habitable planet like its neighbour Earth. This paper presents a meta-study of existing observations of Venus' upper atmosphere and exosphere and an exospheric model of the thermal and hot atmosphere of Venus above the homopause. Mass spectra for possible future Venus missions are predicted, as for example the EnVision mission of ESA. The main focus are the heavy noble gases and requirements for the trajectories are proposed. In addition, mass spectra and recommended integration times for the Venus flyby of ESA's JUICE mission are derived. • Kr and Xe can be measured in Venus' atmosphere during an aerobraking operation. • Xenon is detectable in Venus' atmosphere with a 1 s integration below 123 km. • Krypton is detectable in Venus' atmosphere with a 1 s integration below 135 km. [ABSTRACT FROM AUTHOR]

Impacts of horizontal winds assimilation on thermal tides are investigated by using the Venus atmospheric general circulation model for the Earth Simulator local ensemble transform Kalman filter data assimilation system. The assimilated data are horizontal winds derived from Venus ultraviolet images taken by the Venus Monitoring Camera onboard the Venus Express orbiter. The results show that three‐dimensional structures of the thermal tides are significantly improved not only in the horizontal winds but also in the temperature field, even though the observations are available only at the cloud top level on the southern dayside hemisphere approximately once an Earth day. The reproduced temperature fields agree well with recent radio occultation measurements of the Venus Climate Orbiter Akatsuki. The zonal mean fields of the zonal wind and temperature are also improved globally. This study would enable reanalysis of past Venus observations. Key Points: Three‐dimensional structures of the thermal tides are significantly improved by the data assimilation of horizontal winds derived from Venus UV imagesReproduced temperature fields agree well with those obtained by radio occultation measurements of AkatsukiZonally averaged atmospheric structures are improved globally even though the observations are very limited in space and time [ABSTRACT FROM AUTHOR]

The Venusian atmosphere is covered by clouds with superrotating winds whose accelerating mechanism is still not well understood. The fastest winds, occurring at the cloud tops (∼70‐km height), have been studied for decades, thanks to their visual contrast in dayside ultraviolet images. The middle clouds (∼50–55 km) can be observed at near‐infrared wavelengths (800–950 nm), although with very low contrast. Here we present the first extensive analysis of their morphology and motions at lower latitudes along 2016 with 900‐nm images from the IR1 camera onboard Akatsuki. The middle clouds exhibit hemispherical asymmetries every 4–5 days, sharp discontinuities in elongated "hook‐like" stripes, and large contrasts (3–21%) probably associated with large changes in the optical thickness. Zonal winds obtained with IR1 images and with ground‐based observations reveal mean zonal winds peaking at the equator, while their combination with Venus Express unveils long‐term variations of 20 m/s along 10 years. Plain Language Summary: The atmosphere Venus is surprisingly fast with velocities 60 times faster than the solid globe of Venus. This atmospheric phenomenon is called superrotation and its mechanisms are yet unexplained for the scientists. The Japanese space mission Akatsuki from the Japan Aerospace Exploration Agency arrived at Venus in December 2015 to try to unveil this mystery. Among its instruments, the camera IR1 was prepared to observe the middle clouds of Venus (50–55 km over the surface), which are the most unknown and hardest to observe since they normally exhibit very low contrast in the images. Thanks to the images from the camera IR1, we have observed with high spatial resolution the middle clouds of Venus along the first year of observations of Akatsuki, discovering that they exhibit higher contrasts than expected and a wide variety of cloud patterns unrelated to what we observe at the top of the clouds (70 km above the surface). Finally, the motions of the middle clouds obtained through the combination of images from Akatsuki, amateur observers and the past mission Venus Express, have allowed to reconstruct a composite of the winds of Venus along 10 years, unveiling that the superrotation may be subject to long‐term variabilities unreported before. Key Points: First extensive study (more than a year) of the middle clouds of Venus at low latitudes combining Akatsuki and ground‐based observationsCloud morphologies observed at high spatial resolution and with high contrasts suggest important differences between middle and upper cloudsMiddle cloud winds peak at the equator and have long‐term variations when compared with results from previous missions [ABSTRACT FROM AUTHOR]

Highlights • Solar-locked and geographical atmospheric structures on Venus are investigated. • The present study evaluates differences between zonal and dayside averages. • Indirect circulation is formed at high latitudes by thermal tide and baroclinic waves. • Stationary modification of middle-atmospheric structure is forced by topography. • Solar-locked wind fields are compared with the Akatsuki UV cloud tracked ones. Abstract Solar-locked and geographical atmospheric structures of daily averaged wind and temperature on Venus were investigated using an atmospheric general circulation model with Venusian topography and a two-stream radiative code and were compared with wind fields obtained from the Akatsuki ultraviolet imager. The horizontal wind fields simulated around the subsolar region are similar to the observed ones at the cloud top. Mid-latitude jets of ∼120 m s–1 and an equatorial fast flow of ∼90 m s–1 are formed around the cloud top. A poleward flow of >8 m s–1 is formed above the cloud layer, where solar heating is strong. Around the cloud top, a poleward flow of ∼1 m s–1 is confined within the equatorward flank of the jet core, whereas an indirect circulation is formed in the jet core by the eddy heat fluxes owing to the thermal tide and baroclinic waves. In solar-fixed coordinates, the subsolar-to-antisolar circulation is predominant around the cloud top. Thus, differences are significant between the zonal and dayside averages of the meridional wind and its related fluxes within the cloud layer. This suggests the zonal mean meridional wind of the Hadley circulation, eddy momentum, and heat fluxes from the one-side hemisphere must be estimated carefully. In the experiment including topography, a near-surface subrotation is formed in latitudinal zones over high land and mountains, a weakly stable layer is formed at 10–20 km at low latitudes, and the zonal wind is weakened at the cloud top over the Aphrodite Terra. Regional stationary modification of the atmospheric structure due to topographical waves appears in the cloud layer. [ABSTRACT FROM AUTHOR]

Highlights • The rock analyzed at the Venera 8 landing site is thought to be silicic. • Fractional crystallization of Venusian basalt can produce the theoretical Venera 8 rock. • It is possible that sialic crust was encountered at the Venera 8 landing site. Abstract The surface rock composition measured by gamma (γ)-ray spectrometry at the Venera 8 landing site has anomalously high Th (6.5 ± 2.2 ppm) and U (2.2 ± 0.7 ppm) concentrations with respect to the material analyzed at other landing sites (Vega 1, Vega 2, Venera 9, Venera 10). A calculated bulk rock composition of Venera 8, constrained by the measured Th, U and K 2 O (4.0 ± 1.2 wt%) contents, is similar to silicic to intermediate rocks (diorite/granodiorite) that are typical of terrestrial convergent margins (magnesian, calc-alkalic). In this study, major and trace elemental modeling is applied in order to determine if the calculated whole rock composition of Venera 8 can be derived from a parental magma composition similar to Venusian basalt. The modeling results indicate that polybaric fractional crystallization of a hydrous (H 2 O = 0.4 wt%) and relatively oxidizing (ΔFMQ + 0.7) parental composition similar to Venera 14 basalt can yield residual silicic liquids that match the calculated Venera 8 whole rock composition. The measured Th and U concentrations can also be reproduced within the data uncertainty. Although Venus lacks modern Earth-style plate tectonics, magnesian, calc-alkalic compositions are common within Archean greenstone belts and some rift settings (Haida Gwaii). Consequently, it is possible that the Venera 8 probe encountered a fragment of crust that resembles a terrestrial greenstone belt. [ABSTRACT FROM AUTHOR]

Highlights • First detection of cloud top ozone in Venus atmosphere (about 1000 times less than Earth). • Ozone presence is restricted to high latitudes (polewards of 50°) in both hemispheres. • Measurements are qualitatively supported by our 3D photochemical model. Abstract After the first sporadic detections of an ozone (O 3) nighttime layer in the 90–100 km altitude range (Montmessin et al., 2011), we report here the discovery of another, permanent ozone layer on Venus, restricted to high latitudes (polewards of 50° both N and S) and located at the upper cloud level near 70 km. This detection was performed during a reanalysis of the whole SPICAV-UV nadir dataset through UV absorption near 250 nm in the backscattered solar light. The O 3 volume mixing ratio peaks in the 10–20 ppbv range, yielding observable column densities in the 0.1–0.5 Dobson units (DU), comparable to nominal values on Mars but much smaller than for Earth (∼ 300 DU). These measurements are supported by our 3D-photochemical model coupled with the LMD-IPSL GCM (Lebonnois et al., 2010), which indicates that the ozone layer identified by SPICAV results from downward transport of O 2 (∼ 50 ppmv) molecules over the poles by the mean meridional circulation. Our findings do not contradict previous upper limits (< 2 ppmv) based on O 2 measurements (Mills, 1999), since they were restricted to lower latitudes only. [ABSTRACT FROM AUTHOR]