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The terrestrial planet Venus is classified by astronomers as an inferior planet because it is located closer to the Sun than the Earth. Venus orbits the Sun at a mean distance of 108.21 Million Km and receives an average annual solar irradiance of 2601.3 W/m 2 , which is 1.911 times that of the Earth. A set of linked forward and inverse climate modelling studies were undertaken to determine whether a process of atmospheric energy retention and recycling could be established by a mechanism of energy partition between the solid illuminated surface and an overlying fully transparent, non-greenhouse gas atmosphere. Further, that this atmospheric process could then be used to account for the observed discrepancy between the average annual solar insolation flux and the surface tropospheric average annual temperature for Venus. Using a geometric climate model with a globular shape that preserves the key fundamental property of an illuminated globe, namely the presence on its surface of the dual environments of both a lit and an unlit hemisphere; we established that the internal energy flux within our climate model is constrained by a process of energy partition at the surface interface between the illuminated ground and the overlying air. The dual environment model we have designed permits the exploration and verification of the fundamental role that the atmospheric processes of thermal conduction and convection have in establishing and maintaining surface thermal enhancement within the troposphere of this terrestrial planet. We believe that the duality of energy partition ratio between the lit and unlit hemispheres applied to the model, fully accounts for the extreme atmospheric “greenhouse effect” of the planet Venus. We show that it is the meteorological process of air mass movement and energy recycling through the mechanism of convection and atmospheric advection, associated with the latitudinal hemisphere encompassing Hadley Cell that accounts for the planet’s observed enhanced atmospheric surface warming. Using our model, we explore the form, nature and geological timing of the climatic transition that turned Venus from a paleo water world into a high-temperature, high-pressure carbon dioxide world.

Solar balloons are a promising platform for providing multi-hour flights in and above the upper cloud layer of Venus. The temperature and pressure profiles from 55–75 km above the surface of Venus are very similar to Earth’s from sea level to approximately 30 km, the site of numerous terrestrial solar balloon missions. Additionally, Venus’s highly reflective cloud layer can provide a higher intensity of reflected solar radiation. An ideal solar balloon envelope incorporates a lightweight material that has a high absorbtivity in the visual spectrum, and a low emissivity in the infrared spectrum. The envelope then absorbs direct, reflected, and diffuse radiation, as well as infrared radiation, and heats up the internal balloon air through conduction, resulting in passive flight without the need for an external heat source or lifting gas. This work builds on previous high altitude and solar balloon models and adapts them for Venus’ atmosphere to explore their expected payload mass capacity and flight times. The possible equilibrium float altitudes for various system masses and solar zenith angles are compared between Earth and Venus. Finally, an Earth simulation is compared to terrestrial solar balloon mission data to validate the model and further demonstrate the feasibility of solar balloon flight on Venus.

Although terrestrial wireless communications often must function under harsh environmental conditions, there are peculiar demands on communications systems for planetary exploration. For example, the mil-spec electronics temperature range is generally regarded as −55–+125 °C. A probe on the surface of Venus will experience a nearly constant operational temperature of +460 °C. Conversely, the temperature of Europa at the equator never exceeds ≈−140 °C, and the temperature at the poles never exceeds ≈−220 °C. The (physical layer) communications channel for each represents unique challenges, which are described. For example, RF opacity of the toxic Venus atmosphere is inversely proportional to wavelength ${(}\mathit{\lambda}{)}$ squared, imposing an upper limit to a viable lander-to-orbiter link frequency. Similarly, communicating from Europa’s presumed deeply buried liquid ocean through a thick, briny (electrically conductive) ice layer renders a conventional RF link useless. Plus, Europa receives approximately 5.4 Sv of radiation per day, roughly 1,000 times the average annual dose experienced by humans on Earth (only a fraction of that comes from outer space).

The antifriction properties have been determined experimentally for a carbon–carbon composite in the course of sliding friction against 40Kh13 steel in an environment of carbon dioxide. Changes in the friction coefficient upon heating to 800°C have been investigated in the velocity ranges from 0.05 to 0.25 m/s at a contact pressure ranging within 0.5–1 MPa. The novelty of the investigation consists in determining the tribotechnical properties of a little-studied friction pair that is promising for use in aerospace technology. Particular attention is paid to the tribotechnical properties of the friction pair at 500°C. Based on the studies, the friction coefficient is recommended for the design of plain bearings and hinges for spacecraft intended for operation in the atmosphere of Venus.

The radio occultation measurements of the signal intensity (λ = 32 cm) of the Venera-15 and -16 satellites, carried out from October 16 to October 31, 1983, are used to analyze the activity of internal waves in the northern polar atmosphere of Venus. Observations of the intensity of radio waves provide important information about the fine-scale structure of the planet’s atmosphere. Comparison of radio occultation measurements and the results of the standard wave theory shows that small-scale fluctuations of the received signal intensity are caused by the spectrum of vertically propagating internal gravity waves. The vertical length of these fluctuations at altitudes of more than 61.5 km is about ~1 km. The model developed for the radiative damping of intensity fluctuations with altitude in the atmosphere of Venus assumes that the intrinsic frequencies of the identified internal waves (measured in a frame of reference moving together with the undisturbed flow) in the sessions under study vary from 3.5 × 10–4 to 9.5 × 10–4 rad/s, and the ratio of horizontal and vertical wavelengths is in the range from 57 to 21.

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.

Materials used in the fabrication of landers for Venus exploration need to be carefully selected to assure functional durability throughout anticipated prolonged future mission durations in the har...

The spectroscopy of cis-OSSO and trans-OSSO is explored and put into the context of the Venusian atmosphere, along with other sulfur compounds potentially present there, namely, S2O, C1-S2O2, trigonal-S2O2, and S3. UV-vis spectra were calculated using the nuclear ensemble approach. The calculated OSSO spectra are shown to match well with the 320-400 nm near-UV absorption previously measured on Venus, and we discuss the challenges of assigning OSSO as the Venusian near-UV absorber. The largest source of uncertainty is getting accurate concentrations of sulfur monoxide (3SO) in the upper cloud layer of Venus (60-70 km altitude) since the 3SO self-reaction is what causes cis- and trans-OSSO to form. Additionally, we employed the matrix-isolation technique to trap OSSO formed by microwave discharging a gas mixture of argon and SO2 and then depositing the mixture onto a cold window (6-12 K). Anharmonic vibrational transition frequencies and intensities were calculated at the coupled cluster level to corroborate the matrix-isolation FTIR spectra. The computationally calculated UV-vis and experimentally recorded IR spectra presented in this work aid future attempts at detecting these sulfur compounds in the Venusian atmosphere.

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.

Explaining super-rotation on Venus The solid surface of Venus rotates very slowly, once every 243 days, but its thick atmosphere circles the planet in just 4 days. This phenomenon, known as super-rotation, requires a continuous input of angular momentum, from an unknown source, to overcome friction with the surface. Horinouchi et al. mapped the planet's winds using ultraviolet observations of Venus' clouds from the orbiting Akatsuki spacecraft (see the Perspective by Lebonnois). They incorporated these data into a global model of angular momentum transport in the atmosphere, finding that the super-rotation is maintained through thermal tides driven by solar heating. Science , this issue p. 405 ; see also p. 363

Despite the harsh conditions in the atmosphere of Venus, the possibility for an aerial habitable zone exists. A thermal habitable zone is predicted to exist at an altitude range of 62 to 48 km, above which temperatures drop below the lower thermal limit of cell growth and below which temperatures exceed the evaporation temperature. Many biocidal factors must be considered for the complete definition of an aerial habitable zone; in this study we consider the constraint specifically from the perspective of biocidal solar ultraviolet (UV) intensity in the atmosphere. We simulated the penetration of solar ultraviolet and visible light through the atmosphere using a radiative transfer model, to determine the spectral environment (and thus the UV biocidal effect) as a function of altitude in the atmosphere of Venus. At the top of the thermal aerial habitable zone (62 km) the incoming solar irradiance creates a severely challenging UV environment, with extremophiles such as Deinococcus radiodurans expected to be able to endure these UV conditions for approximately 80 s. At an altitude of around 59 km the biologically-weighted UV irradiance drops below that calculated for the Archean Earth, and continues to fall with decreasing altitude until at 54 km it is less than that found currently at the surface of Earth. Crucially, longer wavelength photosynthetically active light continues to penetrate to these altitudes and below, resulting in a solar radiation environment in the venusian atmosphere below around 54 km that screens biologically-damaging UV radiation yet permits the process of photosynthesis. Whilst not claiming to suggest the existence of an aerial habitable zone in general, by considering thermal conditions, ionising radiation and the UV flux environment of the venusian cloud deck alone, we define a potential habitable zone that extends from 59 km to 48 km. This region should form the focus of future remote and in situ astrobiological investigations of Venus.

Small, expendable drop probes are an attractive method for making measurements in the lower atmosphere of Venus, \,augmenting the capabilities of orbiters or aerial platforms that must remain in the benign temperature region above 50 km altitude. However, probe miniaturization is impeded by the need to provide thermal and pressure protection for conventional payloads. This paper determines the minimum mass limits for an insulated pressure vessel probe that operates all the way to the Venusian surface. Scaling laws for the probe performance and mass of major system components are explicitly derived using a simple model that captures the relevant physics. Streamlining the probe is found to be a highly effective strategy for lowering the system mass, but it also reduces the time available for data collection and transmission. Tradeoffs, guidelines and design charts are presented for an array of miniaturized probes. Total system masses on the order of 5 kilograms are plausible with streamlined probes if the desired science measurements can be performed faster than a standard Venus descent timeline.

To evaluate a recent hypothesis of species stratification in the Venus lower atmosphere, a time-dependent, three-dimensional model is proposed for studying turbulent mixing of many species in the Venus lower atmosphere. This model is based on fundamental physics embedding non-equilibrium thermodynamics, the Onsager classical relationship between fluxes and forces, high-pressure transport property calculation and a real-gas equation of state. The conservation equations are self-contained, with no need for coefficients based on parametrizations to match Venus observations. The rationale for solving these equations in relatively small spatial domains at different altitudes in the Venus lower atmosphere is presented. The equations are solved in a temporal mixing layer configuration that is eminently suited to investigate turbulent mixing between two streams of different composition. The adopted simulation method is Direct Numerical Simulation (DNS). A substantial database of DNS realizations is generated for mixtures of two and seven species, with different levels of initial stratification, and at the realistic conditions of pressures and temperatures in the Venus lower atmosphere at three altitudes. High density-gradient magnitude regions (HDGM) are shown to form under initial high stratification conditions, with larger gradient values obtained at low altitudes where supercritical conditions occur. Independent of the altitude lower than 50 km, under low stratification conditions, mixing produces a more uniform spatial distribution of the density than at higher initial stratification. Under low initial stratification conditions, the influence of the minor species on the global behavior of the flow seems to be negligible. At high initial stratification conditions, differences in diffusion of various species play an important role in determining the mixture characteristics. The hypothesis of chemical species separation is discussed in the light of the present results which do not support the existence of stable species separation in the lower Venus atmosphere, independent of the number of species or the altitude.

Мы разработали оригинальный метод идентификации дискретных волновых событий и восстановления характеристик внутренних гравитационных волн (ВГВ), используя анализ индивидуального высотного профиля температуры, плотности или квадрата частоты Брента-Вяйсяля в атмосфере планет земной группы. Радиационное затухание в атмосфере Венеры на высотах более ~65 км является основным процессом диссипации внутренних волн с вертикальной длиной волны, We developed an original method for identifying discrete wave events and reconstructing the characteristics of internal gravity waves (IGWs) using the analysis of an individual altitude profile of temperature, density, or Brunt-Vaisala frequency squared in the atmosphere of terrestrial planets. Radiative attenuation in the atmosphere of Venus above ~65 km is the main dissipation process for internal waves with vertical wavelength

Planetary-scale 4-day Kelvin-type waves at the cloud top of the Venus atmosphere have been reported from the 1980s, and their significance for atmospheric dynamics has been pointed out. However, these waves have not been reproduced in Venus atmospheric general circulation models (VGCMs). Recently, horizontal winds associated with the planetary-scale waves at the cloud top have been obtained from cloud images taken by cameras onboard Venus orbiters, which could enable us to clarify the structure and roles of Kelvin-type waves. In order to examine this possibility, our team carried out an idealized observing system simulation experiment (OSSE) with a data assimilation system which we developed. The wind velocity data provided by a CCSR/NIES (Center for Climate System Research/National Institute for Environmental Studies) VGCM where equatorial Kelvin-type waves were assumed below the cloud bottom was used as idealized observations. Results show that 4-day planetary-scale Kelvin-type waves are successfully reproduced if the wind velocity between 15&deg, S and 15&deg, N latitudes is assimilated every 6 h at 70 km altitude. It is strongly suggested that the Kelvin-type waves could be reproduced and investigated by the data assimilation with the horizontal wind data derived from Akatsuki ultraviolet images. The present results also contribute to planning future missions for understanding planetary atmospheres.

Compared to the diversity seen in exoplanets, Venus is a veritable astrophysical twin of the Earth, however its global cloud layer truncates features in transmission spectroscopy, masking its non-Earth-like nature. Observational indicators that can distinguish an exo-Venus from an exo-Earth must therefore survive above the cloud layer. The above-cloud atmosphere is dominated by photochemistry, which depends on the spectrum of the host star and therefore changes between stellar systems. We explore the systematic changes in photochemistry above the clouds of Venus-like exoplanets orbiting K-Dwarf or M-Dwarf host stars, using a recently validated model of the full Venus atmosphere (0-115 km) and stellar spectra from the MUSCLES Treasury survey. SO2, OCS and H2S are key gas species in Venus-like planets that are not present in Earth-like planets, and could therefore act as observational discriminants if their atmospheric abundances are high enough to be detected. We find that SO2, OCS and H2S all survive above the cloud layer when irradiated by the coolest K-Dwarf and all seven M-Dwarfs, whereas these species are heavily photochemically depleted above the clouds of Venus. The production of sulfuric acid molecules that form the cloud layer decreases for decreasing stellar effective temperature. Less steady-state photochemical oxygen and ozone forms with decreasing stellar effective temperature, and the effect of chlorine-catalysed reaction cycles diminish in favour of HOx and SOx catalysed cycles. We conclude that trace sulfur gases will be prime observational indicators of Venus-like exoplanets around M-Dwarf host stars, potentially capable of distinguishing an exo-Venus from an exo-Earth., 30 pages, 15 figures, 2 tables, accepted for publication in The Astrophysical Journal

A cloud opacity contrast feature that has been called a “long-lived sharp disruption” has been seen in the atmosphere of Venus in the near-infrared using Akatsuki’s IR2 camera, most clearly at equatorial latitudes. This feature was found to have a consistent planet-circling period of 4.9 days, and subsequent searches of past imagery revealed that it has probably existed for at least 30 years, the duration of near-infrared investigation of the deep atmosphere of Venus. Guided by the remarkably consistent morphological appearance of this feature, we have identified at least one previous instance of it in the Venus Express Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) data. We take advantage of the spectroscopic capabilities of VIRTIS to retrieve atmospheric parameters in the vicinity of this feature that cannot be retrieved using the limited filter selection on board Akatsuki. We find that the changes in measurable quantities, such as cloud particle acid mass fraction, water vapor, carbon monoxide, cloud base altitude, and particle size, suggest that the changes that take place in the vicinity of this feature are restricted to the lower clouds of Venus (below 50 km). We hypothesize that further evolution of this feature (over timescales of days to weeks) results in measurable variations in these parameters at altitudes in the middle clouds of Venus (50–57 km), lending credence to its identification as a baroclinic trough or Kelvin front.

The detection of phosphine (PH3) in the atmosphere of Venus has been recently reported based on millimeter-wave radio observations (Greaves et al. 2020), and its re-analyses (Greaves et al. 2021a/b). In this Matters Arising we perform an independent reanalysis, identifying several issues in the interpretation of the spectroscopic data. As a result, we determine sensitive upper-limits for PH3 in Venus' atmosphere (>75 km, above the cloud decks) that are discrepant with the findings in G2020 and G2021a/b. The measurements target the fundamental first rotational transition of PH3 (J=1-0) at 266.944513 GHz, which was observed with the James Clerk Maxwell Telescope (JCMT) in June 2017 and with the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2019. This line's center is near the SO2 (J=309,21-318,24) transition at 266.943329 GHz (only 1.3 km/s away from the PH3 line) which represents a potential source of contamination. The JCMT and ALMA data, as presented in G2020, are at spectral resolutions comparable to the frequency separation of the two lines. Moreover, the spectral features identified are several km/s in width, and therefore do not permit distinct spectroscopic separation of the candidate spectral lines of PH3 and SO2. We present the radiative transfer modelling we have performed and then discuss the ALMA and JCMT analyses in turn.

Several chemicals which could be relevant for life processes are found in the upper atmosphere of Venus (H2S, OCS, SO2, NH4Cl, NH2COOHN4 and H2O). Moreover, the atmosphere instability and the reason for the high ultraviolet (UV) heterogeneous absorption between 320 and 400 nm in the top cloud layer and mesosphere (~ 40-70 Km) are still disputed phenomena. These scientific points could be further studied by small UV Raman and fluorescence instruments mounted in a small lander platform (< 20 kg) being send to Venus. In this current article we will propose an optical payload mission, which could be useful to give more information on these scientific questions. This study proposes a feasibility analysis for launching a small probe device that includes an emitting laser, a receiving telescope and a detector. The goal of this theoretical mission (UV-BIOmarker Mapper for Venus AtmosPhere or UV-BIOMAP) will be to analyse the laser-emitted and further absorption of UV light in the Venus atmosphere, and to verify the possible presence of biomarkers. The current state of the art of the required technologies to be implemented would allow a more cost-efficient and easy to develop mission, compared with previously completed Venus probes. This article will be focused on the required science and optical payload devices needed for solving these issues. Requirements for mass and power budgets for the optical payload will be analysed to ensure that the mission can be carried out at relatively low cost while still accomplishing the scientific goals of revealing the composition of Venus’s atmosphere in more detail and the reason for the heterogeneous UV absorption in the planet’s top cloud layer and mesosphere.

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.

Using an in-house developed one dimensional photo-chemical model (1D-PCM), which considers production and loss of 11 ions namely, CO 2 + , CO + , C + , N 2 + , N + , He + , O + ( 2 D ) , O + ( 2 P ) , O + ( 4 S ) , O 2 + and NO + , characteristics of the V2 layer in the Venus ionosphere has been studied. It is noted that existing ionospheric model for the Venus ionosphere, such as the IonA (Ionization in Atmospheres) model, not only over/under estimate the peak electron density of V2 layer, it also has significant departures from the observations on the solar zenith angle and solar activity control. The IonA model uses VenusGRAM model (Venus Global Reference Atmosphere Model) as input for the neutral density and temperature and considers Venus atmosphere consisting of CO2, O, and N2 molecules only. Further, it oversimplifies the ion chemistry by assuming Venus ionosphere to have O 2 + as the only dominant ion species. Using VTS3 model, an empirical model based on measurements from Orbiter Neutral Mass Spectrometer on Pioneer Venus Orbiter (PVO) which considers profiles of six neutrals (CO2, O, CO, He, N, and N2), we modified IonA model, named as IonA-VTS3, to find that it reproduced the altitude of V2 peak electron density (hmV2) quite well. However, the model still lacked in reproducing observed peak V2 electron density (NmV2). The in-house developed one dimensional photo-chemical model (1D-PCM) not only estimated NmV2 accurately, the hmV2 was also reproduced quite well. Comparison of Venera and PVO radio occultation measurements with 1D-PCM and IonA-VTS3 calculations reveals the role of complex chemical reactions in determining the features of peak altitude and density of V2 layer during different solar activity periods. We surmised that differences in the observed and IonA modeled peak V2 layer altitudes were due to the limitations associated with VenusGRAM neutral density model. It shows that variations in the neutral density controls the V2 layer peak density height. 1D-PCM calculations also showed that the complex chemistry including production and loss reactions of 11 ions could reproduce the variations in the peak density of Venusian ionosphere during different solar activity conditions. It suggests that the ion-chemistry has wider control over the peak plasma density in the Venus ionosphere.

著者人数: 13名, Accepted: 2018-11-28, 資料番号: SA1180242000

Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, favorable chemical ingredients and energy pathways. If life ever developed on, or was transported to, early Venus from elsewhere, it might have thrived, expanded and then survived the changes that have led to an inhospitable surface on Venus today. The Venus cloud layer may provide a refugium for extant life that persisted from an earlier more habitable surface environment. We introduce the Venus Life Equation - a theory and evidence-based approach to calculate the probability of extant life on Venus, L, using three primary factors of life: Origination, Robustness, and Continuity, or L = O x R x C. We evaluate each of these factors using our current understanding of Earth and Venus environmental conditions from the Archaean to the present. We find that the probability of origination of life on Venus would be similar to that of the Earth and argue that the other factors should be nonzero, comparable to other promising astrobiological targets in the solar system. The Venus Life Equation also identifies poorly understood aspects of Venus that can be addressed by direct observations with future exploration missions., Revision resubmitted after review to Astrobiology for Venus Special issue. 37 pages, 4 figures. Shorter version submitted as white paper in shortened form to Planetary and Astrobiology Decadal Survey

This is a white paper submitted to the Planetary Science and Astrobiology Decadal Survey. The deep atmosphere of Venus is largely unexplored and yet may harbor clues to the evolutionary pathways for a major silicate planet with implications across the solar system and beyond. In situ data is needed to resolve significant open questions related to the evolution and present-state of Venus, including questions of Venus' possibly early habitability and current volcanic outgassing. Deep atmosphere "probe-based" in situ missions carrying analytical suites of instruments are now implementable in the upcoming decade (before 2030), and will both reveal answers to fundamental questions on Venus and help connect Venus to exoplanet analogs to be observed in the JWST era of astrophysics.

One of the most important questions in planetary science is the origin of the current Venus atmosphere, its relationship and coupling to Venus’ geologic and geodynamic evolution, andwhy it is so different from that of the Earth. We specifically address the following question:Does the eruption of the total volume of extrusive volcanic deposits observed in the exposed geologic record of Venus contribute significantly to the current atmosphere through volatile release during emplacement of the extruded lavas? To address this question, we used the observed geologic and stratigraphic record of volcanic units and features, and their volumes, as revealed by Magellan (1; their Fig. 26 and Table 5). We converted the volumes of the main volcanic units to lava/magma masses using a density of 3000 kg m-3. Next, we chose the upperthickness values, and added the contributions from allof the units; summing the values of the "total eruptives" gives the absolute upper limit estimate of the mass of documented volcanics that could contribute to the atmosphere, 7.335 x 1020 kg. We then compare this with the current mass of the Venus atmosphere (4.8 x 1020 kg). We find that in order to make the current atmosphere from the above volcanics, the magma would have to consist of 65.4% by mass volatiles, which is, of course, impossible. We conclude that the grand totalof the currently documented volcanics can not have produced other than a very small fraction of the current atmosphere.Exsolution of volatiles during volcanic eruptions is significantly dependent on surface atmospheric pressure (2-3). However, the total volumeof lava erupted in the period of global volcanic resurfacingis still insufficient to produce the CO2atmosphere observed today, even if the ambient atmospheric pressure at that time was only 50% of what it is today. Therefore, a very significant part of the current CO2atmosphere must have been inherited from a time prior to the observed geologic record, sometime in the first ~80% of Venus history. Furthermore, the total volumeof lava erupted in the stratigraphically youngest period of the observed record (1) is insufficient to account for the current abundance of SO2 in the atmosphere; thus, it seems highly unlikely that current and recently ongoing volcanism could be maintaining the currently observed ‘elevated’ levels of SO2 in the atmosphere (4). In addition, because of the fundamental effect of atmospheric pressure on the quantity of volatiles that will be degassed, varying the nature of the mantle melts over a wide range of magma compositions and mantle fO2 appears to have minimal influence on the outcome. We conclude that the current Venus atmosphere must be a “fossil atmosphere”, largely inherited from a previous epoch in Venus history, and if so, may provide significant insight into the conditions during the first 80% of Venus history.(1) Ivanov and Head (2013) Plan. Space Sci. 84, 66; (2) Gaillard & Scaillet, 2014, EPSL 403, 307; (3) Head & Wilson, 1986, JGR 91, 9407;(4)Esposito, 1984, Science 223, 1072.

International audience; A numerical simulation of the upper atmosphere of Venus is carried out with an improved version of the Institut Pierre-Simon Laplace (IPSL) full-physics Venus General Circulation Model (GCM). This simulation reveals the organization of the atmospheric circulation at an altitude above 80 km in unprecedented detail. Converging flow towards the antisolar point results in supersonic wind speeds and generates a shock-like feature past the terminator at altitudes above 110 km. This shock-like feature greatly decreases nightside thermospheric wind speeds, favoring atmospheric variability on a hourly timescale in the nightside of the thermosphere. A 5-day period Kelvin wave originating in the cloud deck is found to substantially impact the Venusian upper atmosphere circulation. As the Kelvin wave impacts the nightside, the poleward meridional circulation is enhanced. Consequently, recombined molecular oxygen is periodically ejected to high latitudes, explaining the characteristics of the various observations of oxygen nightglow at 1,27 µm. An analysis of the simulated 1,27µm oxygen nightglow shows that it is not necessarily a good tracer of the upper atmospheric dynamics, since contributions from chemical processes and vertical transport often prevail over horizontal transport. Moreover, dayside atomic oxygen abundances also vary periodically as the Kelvin wave momentarily decreases horizontal wind speeds and enhances atomic oxygen abundances, explaining the observations of EUV oxygen dayglow. Despite the nitrogen chemistry not being currently included in the IPSL Venus GCM, the apparent maximum NO nightglow shifted towards the morning terminator might be explained by the simulated structure of winds.

The purpose of studying the Venus’s atmosphere is to model and simulate Venus’s environment. One of the key parameters of the Venus’s atmosphere is diffusion coefficient. Experimental measurements of diffusion coefficients are particularly difficult under Venus’s environmental conditions. Molecular dynamics have become an important method for studying the properties and dynamics of microscopic systems. In this paper, the equilibrium molecular dynamics (EMD) simulations are used to calculate the interdiffusion coefficients of carbon dioxide (CO2) and nitrogen (N2) at room temperature and pressure in combination with Darken's equation. And the results are compared with experimental values and empirical equations to verify the rationality of the calculation method and the accuracy of the results. The interdiffusion coefficients of trace gases on the surface of Venus for the CO2 system in different states and the CO2-N2 interdiffusion coefficients with altitude in the Venus environment are given. The results show that the diffusion coefficients of the gases on the surface of Venus are two orders of magnitude smaller than those in the Earth's atmosphere and molecular dynamics simulations can well predict the diffusion characteristics of the Venus’s atmosphere and support the simulation of the Venus’s surface environment and the Venus’s atmosphere model.

The exploration of the surface geology of Venus has been hampered by its inhospitable conditions and thick and opaque atmosphere. Fundamental properties, such as crustal composition and heterogenei...

Phosphine (PH3) is proposed to be a possible biomarker in planetary atmospheres and has been claimed to have been observed in the atmosphere of Venus, sparking interest in the habitability of Venus’s atmosphere. Observations of another biomarker, methane (CH4), have been reported several times in the atmosphere of Mars, hinting at the possibility of a past or present biosphere. The Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter has a spectral range that includes several absorption lines of PH3 with line strengths comparable to previously observed CH4 lines. The signature of PH3 was not observed in the 192 observations made over a full Martian year of observations, and here we report upper limits of 0.1–0.6 ppbv.

International audience; The nighttime ozone and sulfur dioxide distributions were analyzed using the entire SPICAV‐UV/Venus Express stellar occultation dataset. After the discovery of an ozone layer at 100 km in the mesosphere reported by Montmessin et al. (2011), 132 other detections were made during the entire 8 years long observing period of the SPICAV UV instrument. In the rare detections the peak abundances of O3 accumulating in the mesosphere are observed with densities from 107 to 108 molecules⋅cm‐3 at 85‐110 km. The ozone layer is estimated to vary from 1 ppbv to 30 ppbv at 85‐95 km while at 95‐105 km the VMR is expected within an interval from 6 ppbv to 120 ppbv. Below 93 km, a puzzling decrease of mixing ratio is observed toward midnight at 30°N. Our work also provides an improved sequel to the analysis of the sulfur dioxide survey previously made in the upper mesosphere by Belyaev et al. (2017). On average, the SO2 content is found to remain constant throughout the vertical profile at a value of around 135±21 ppbv between 85 and 100 km. Rapid and large variations prevent to conclude firmly on any time or space pattern of SO2.

The 1970s were an extraordinarily productive time for Venus research, with space missions making the first direct measurements in its atmosphere and on its surface. The Soviet Union was spectacularly successful, landing a series of spacecraft that sent home the first up-close views of our neighboring world. Venera 7 became the first spacecraft to successfully soft-land on another planet and transmit a signal back to Earth; it made in situ environmental measurements of a broiling, 475∘C surface with a pressure ninety times that at sea level on Earth. The follow-up Venera 8 mission proved that the lower atmosphere of Venus was relatively clear and that its surface rocks were compositionally similar to the basaltic rocks of our own planet. In October 1975, Venera 9 radioed back to Earth the first photographs taken at the surface of Venus, revealing an expanse of plate-like rocks showing no evidence of erosion. Later in the decade, the Americans flew both spacecraft in the Pioneer Venus series, one of which continued relaying data back to Earth for almost 15 years. These missions yielded new insights into the composition and structure of the Venus atmosphere, as well as providing the first global map of the planet’s surface, gleaned from radar measurements.

It is proposed to use "lifting body" type of a lander, which has a permissible complication of the structure, compared with a ballistic type of a lander, and lift-to-drag ratio sufficient for solving the existing maneuvering tasks during the descent in the Venus atmosphere in order to achieve the desired landing area. Possible descent trajectories for a lander of this type are considered, including the possibility of making maximum lateral maneuver, while taking into account long-period trajectories with multiple immersions into the dense layers of the atmosphere, a comparison of these trajectories with the descent trajectory of a traditionally used ballistic type of a lander is also made. The use of a maneuverable lander will enable wide outreach of landing areas, as well as decrease the acting loads and widen the range of scientific tasks and research being carried out.

The exploration of the surface geology of Venus has been hampered by its inhospitable conditions and thick and opaque atmosphere. Fundamental properties, such as crustal composition and heterogenei...

Context: ALMA observations of Venus at 267 GHz have been presented in the literature that show the apparent presence of phosphine (PH3) in its atmosphere. Phosphine has currently no evident production routes on the planet's surface or in its atmosphere. Aims: The aim of this work is to assess the statistical reliability of the line detection by independent re-analysis of the ALMA data. Methods: The ALMA data were reduced as in the published study, following the provided scripts. First the spectral analysis presented in the study was reproduced and assessed. Subsequently, the spectrum was statistically evaluated, including its dependence on selected ALMA baselines. Results: We find that the 12th-order polynomial fit to the spectral passband utilised in the published study leads to spurious results. Following their recipe, five other >10 sigma lines can be produced in absorption or emission within 60 km/s from the PH3 1-0 transition frequency by suppressing the surrounding noise. Our independent analysis shows a feature near the PH3 frequency at a ~2 sigma level, below the common threshold for statistical significance. Since the spectral data have a non-Gaussian distribution, we consider a feature at such level as statistically unreliable that cannot be linked to a false positive probability. Conclusions: We find that the published 267-GHz ALMA data provide no statistical evidence for phosphine in the atmosphere of Venus., Accepted for publication in A&A after minor revisions

A model of the Venusian atmosphere examines the production of phosphorus via interactions of cosmic rays and solar particles with sulfur and argon. It is estimated that the stable isotope Phosphorus-31 has been generated between 23.7 and 67.7 micrograms per day given the present atmosphere of Venus and the variability in the flux of cosmic rays. If the maximum amount of phosphorus were converted into phosphine, the corresponding cosmogenic upper limit for phosphine production would be 74.3 +/− 0.8 micrograms per day. Assuming the maximum phosphorus is converted into phosphine with no losses over time, our simulations show that the cosmogenic production of phosphine cannot account for the 20 ppb concentrations reported by Greaves et al. (2020) . Gamma rays and neutrons resulting from cosmic ray interactions are also examined just after they leave the planet.

Although Venus is a terrestrial planet similar to Earth, its atmospheric circulation is much different and poorly characterized1. Winds at the cloud top have been measured predominantly on the dayside. Prominent poleward drifts have been observed with dayside cloud tracking and interpreted to be caused by thermal tides and a Hadley circulation2–4; however, the lack of nightside measurements over broad latitudes has prevented the unambiguous characterization of these components. Here we obtain cloud-tracked winds at all local times using thermal infrared images taken by the Venus orbiter Akatsuki, which is sensitive to an altitude of about 65 kilometres5. Prominent equatorward flows are found on the nightside, resulting in null meridional velocities when these are zonally averaged. The velocity structure of the thermal tides was determined without the influence of the Hadley circulation. The semidiurnal tide was found to have an amplitude large enough to contribute to the maintenance of the atmospheric superrotation. The weakness of the mean meridional flow at the cloud top implies that the poleward branch of the Hadley circulation exists above the cloud top and that the equatorward branch exists in the clouds. Our results should shed light on atmospheric superrotation in other celestial bodies. Cloud-top thermal images obtained by the Akatsuki orbiter show that Venus has almost null mean meridional circulation at the cloud top, because poleward circulation on the dayside is offset by equatorward circulation on the nightside.

The potential detection of phosphine in the atmosphere of Venus has reignited interest in the possibility of life aloft in this environment. If the cloud decks of Venus are indeed an abode of life, it should reside in the "habitable zone" between ~ 50-60 km altitude, roughly coincident with the middle cloud deck, where the temperature and pressure (but not the atmospheric composition) are similar to conditions at the Earth's surface. We map out a precursor astrobiological mission to search for such putative lifeforms in situ with instrument balloons, which could be delivered to Venus via launch opportunities in 2022-2023. This mission would collect aerosol and dust samples by means of small balloons floating in the Venusian cloud deck and directly scrutinize whether they include any apparent biological materials and, if so, their shapes, sizes, and motility. Our balloon mission would also be equipped with a miniature mass spectrometer that should permit the detection of complex organic molecules. The mission is augmented by contextual cameras to search for macroscopic signatures of life in the Venusian atmospheric habitable zone. Finally, mass and power constraints permitting, radio interferometric determinations of the motion of the balloons in Venusian winds, together with in situ temperature and pressure measurements, will provide valuable insights into the poorly understood meteorology of the middle cloud region., Comment: Published in The Astrophysical Journal Letters; 10 pages; 2 figures; 2 tables

Sulfur dioxide is a radiatively and chemically important trace gas in the atmosphere of Venus and its abundance at the cloud-tops has been observed to vary on interannual to decadal timescales. This variability is thought to come from changes in the strength of convection which transports sulfur dioxide to the cloud-tops, {although} the dynamics behind such convective variability are unknown. Here we propose a new conceptual model for convective variability that links the radiative effects of water abundance at the cloud-base to convective strength within the clouds, which in turn affects water transport within the cloud. The model consists of two coupled equations which are identified as a recharge-discharge oscillator. The solutions of the coupled equations are finite amplitude sustained oscillations in convective strength and cloud-base water abundance on 3-9 year timescales. The characteristic oscillation timescale is given by the geometric mean of the radiative cooling time and the eddy mixing time near the base of the convective clouds., 19 pages, 6 figures, accepted in JGR Planets

This study investigates the global characteristics of the Venus lower atmosphere below the cloud layer. Starting from available data regarding species composition, temperature and pressure, the general thermodynamic and transport properties of the Venus lower atmosphere are first computed at altitudes below the cloud layer. The thermodynamic and transport properties are validated with known data. A thermodynamic stability analysis for a variety of potentially existing mixtures is conducted to highlight the sensitivity of the thermodynamic regime to the variation of the species molar fractions. The limits of thermodynamic stability are represented in the thermodynamic phase diagram of the mixture, and thus regions of phase stability and instability are determined. It is found that the Venus lower-atmosphere thermodynamic regime is located in the stable, single-phase regime, with supercritical conditions occurring in the lower few kilometers, thereby validating ad-hoc expectations which have never envisaged the existence of a two-phase regime at those altitudes. Using thermodynamic and transport-property information thus computed, several non-dimensional numbers are calculated. The Prandtl number is first evaluated. Then, the characteristic Reynolds number is estimated for different assumed length scales, showing that, independent of the length scale, the entire lower atmosphere below the cloud deck is in a fully-turbulent flow regime. Finally, the speed of sound and the Mach number are computed as function of altitude. The information obtained from all these calculations fills a scientific void, and may be crucial for the design of landers on the Venus surface.

The main Venus clouds, covering the entire planet between approx. 50 and 70 km altitude, are believed to consist mostly of liquid sulfuric acid. Below the clouds, the temperature is high enough to evaporate those droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. H2SO4(g) is the main absorber of radio waves as was observed in Mariner, Pioneer Venus, Magellan and Venera radio occultation measurements. Radio wave absorption measurements can be used to derive the amount of H2SO4 as well as to estimate upper limits of SO2 in Venus’ atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. Thanks to the orbit of VEX, a wide range of latitudes and local times was covered so that a global picture of the H2SO4(g) ditribution was obtained. We present H2SO4(g) profiles as well as upper limits of sulfur dioxide near the cloud base derived from the X-band radio signal from the entire Venus Express mission. More than 600 H2SO4(g) profiles show the global sulfuric acid vapor distribution covering the northern and southern hemisphere on the day- and night side of the planet. A distinct latitudinal H2SO4(g) and SO2 variation and a southern northern symmetry are clearly visible. Observations over 8 years allow to study also long-term variations. Indications for temporal H2SO4(g) and SO2 variations are found, at least at northern polar latitudes. The results shall be compared with observations retrieved by other experiments onboard Venus Express. Additionally, the observed H2SO4(g) distribution will be compared with results obtained from a mass transport model.

How the super-rotation of the Venusian atmosphere is maintained is an outstanding question of the Venus science and geophysical fluid dynamics. We tackled it by using data from Akatsuki. Prior to that, we revisited the meridional circulation by using past observational data: downward solar flux from entry probe and satellite-based radiation observation. With a very simple assumption, we obtained a meridional circulation consistent with the earlier studies based on radiative transfer computation. The result allowed us to order-estimate the eddy angular-momentum forcing needed to maintain the present super-rotation. We derived the eddy forcing by using cloud-tracking winds and thermal infrared data from Akatsuki. In particular, we focused on the pivotal question on the maintenance of the presentation, which is how the angular momentum (per unit mass) is supplied at its peak around the equatorial cloud top to compensate the deceleration by the meridional circulation. It was revealed that the thermal tides provide it, acting to accelerate the super-rotation, through both the horizontal and the vertical angular-momentum transport. Other waves and large-scale horizontal turbulence are found to counteract it to a weaker degree, in contrast to the earlier expectation from the classical Gierasch-Rossow-Williams mechanism. This study provided a number of by-products, such as the detection of turbulent motion and spectra of wind disturbances. This study was published recently as Horinouchi et al. 2020, Science, 368 (6489), 405-409 and its online supplementary material.