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Based on the successful landings of landing modules (LM) on the surface and the introduction of aerostat probes (AP) into the air, the feasibility of exploring Venus by an AP drifting in the cloud layer of its atmosphere using short-term descents and landings on its surface has been substantiated. Mathematical modeling was performed to confirm the feasibility of short-term AP drops with a scientific package (SP) in a thermostatted compartment for sampling soil, aerosols and gases and remote sensing (RS) in various regions remote from each other near the surface of the planet Venus for their analysis during a long drift at the height of the cloud layer. Using the example of individual SP devices for geochemical and geophysical studies of Venusian rocks, the scenario and capabilities of AP are shown, which significantly expand both the range of scientific tasks to be solved and the capabilities of the scientific equipment itself. [ABSTRACT FROM AUTHOR]

The relatively unconstrained internal structure of Venus is a missing piece in our understanding of the formation and evolution of the Solar System. Detection of seismic waves generated by venusquakes is crucial to determine the seismic structure of Venus' interior, as recently shown by the new seismic and geodetic constraints on Mars' interior obtained by the InSight mission. In the next decade multiple missions will fly to Venus to explore its tectonic and volcanic activity, but they will not be able to conclusively detect seismic waves, despite their potential to detect fault movements. Looking toward the next fleet of Venus missions after the ones already decided, various concepts to measure seismic waves have been proposed. These detection methods include typical geophysical ground sensors already deployed on Earth, the Moon, and Mars; pressure sensors on balloons; and imagers of high altitude emissions (airglow) on orbiters. The latter two methods target the detection of the infrasound signals generated by seismic waves and amplified during their upward propagation. Here, we provide a first comparison between the detection capabilities of these different measurement techniques and recent estimates of Venus' seismic activity. In addition, we discuss the performance requirements and measurement durations required to detect seismic waves with the various detection methods. Our study clearly presents the advantages and limitations of the different seismic wave detection techniques and can be used to drive the design of future mission concepts aiming to study the seismicity of Venus. Plain Language Summary: We do not really know what the interior of Venus looks like. Even the first‐order structure of the size of Venus' core is plagued with large uncertainties. For other planets, such as the Earth and Mars, the interior structure is much better constrained. This is largely thanks to the seismological investigations performed on these planets that revealed their interior structure by studying the seismic waves caused by quakes. In the next decade, new missions will fly to Venus to explore its tectonic and volcanic activity, which is interesting to estimate seismicity. But these missions will not be able to detect any seismic waves. In order to help design future mission concepts, we discuss instruments that could record seismic waves, as already used on the Earth, the Moon, and Mars; instruments on balloons that could float in the Venusian atmosphere; and instruments on spacecrafts that monitor the variations of atmospheric emissions caused by seismic waves originating at the surface. We compare all these different techniques with each other and with recent estimates of Venus' seismic activity to see which of them works best in different scenarios. Key Points: The capabilities of various measurement concepts to detect quakes on Venus are estimated and compared to recent Venus seismicity estimatesGround sensors are limited by their short measurement duration, but also by an atmosphere induced noise that may be above their self noiseAtmospheric seismology concepts are limited to large quake magnitudes, and airglow imagers are favored relative to balloon measurements [ABSTRACT FROM AUTHOR]

Venus' surface and interior dynamics remain largely unconstrained, due in great part to the major obstacles to exploration imposed by its 470°C, 90 bar surface conditions and its thick, opaque atmosphere. Flyby and orbiter‐based thermal emission data provide opportunities to characterize the surface composition of Venus. However, robust interpretations of such data depend on understanding interactions between the planet's surface basaltic rocks and its caustic carbon dioxide (CO2)‐dominant atmosphere, containing trace amounts of sulfur dioxide (SO2). Several studies, using remote sensing, thermodynamic modeling, and laboratory experiments, have placed constraints on basaltic alteration mineralogy and rates. However, constraints on the effects of SO2‐bearing reactions on basalts with diverse compositions remain incomplete. Here, we present new data from a series of gas‐solid reaction experiments, in which samples of two basalt compositions were reacted in an SO2‐bearing CO2 atmosphere, at relevant Venus temperatures, pressure, and oxygen fugacity. Reacted specimens were analyzed by scanning electron microscopy and scanning transmission electron microscopy using sample cross‐sections produced with focused ion beam milling. Surface alteration products were characterized, and their abundances estimated; subsurface cation concentrations were mapped to show the depth of alteration. We demonstrate that the initial development of reaction products progresses rapidly over the course of 30‐day runs. Alkaline basalt samples are coated by Na‐sulfate (likely thenardite, Na2SO4) and amorphous calcium carbonate (CaCO3) alteration products, and tholeiitic basalt samples are primarily covered by anhydrite (CaSO4), Fe‐oxide (FexOy: likely magnetite, Fe3O4), and other minor phases. These mineralogies differ from previous experiments in CO2‐only atmospheres. Plain Language Summary: Surface features on Venus, such as volcanic landforms, and their ages can be studied to infer the planet's interior properties. Venus' thick, opaque atmosphere and extreme temperature and pressure limit a detailed study of its surface. Fortunately, sensors aboard Venus‐orbiting spacecraft can "see" its surface using select wavelengths of light to provide opportunities to interpret the composition of its surface. However, these interpretations rely on understanding how Venus' atmosphere might chemically interact with the surface and what mineral products may result. This is not yet fully understood despite the results of several prior studies with objectives similar to ours. Here, we share the results from experiments that mimic these chemical reactions. We used rock types such as those known to be on the surface of Venus and subjected them to relevant temperatures and pressure and a blend of two reactive gases, carbon dioxide and sulfur dioxide, to model Venus' atmosphere. After the experiments, we examined the rocks with microscopic instruments that allowed us to characterize chemical changes from their surfaces to their interiors. Our interpretations suggest that these reactions occur rapidly and that the compositions of the mineral coatings produced are dictated by the rocks' slightly different compositions. Key Points: Basalts experimentally altered under Venus P‐T conditions and a CO2–SO2 atmosphere produce reaction products of Ca‐ and Na‐sulfates, and Fe‐oxidesAlteration products and the advancement of alteration were strongly dependent upon the compositions of the solid reactantsThe rates at which basalts altered in a CO2–SO2 atmosphere were greater than rates in a CO2‐only atmosphere [ABSTRACT FROM AUTHOR]

Accurate spectroscopic parameters have been obtained for the identification of the [H, Cl, S, O] molecular system in the Venus atmosphere using computational methods. These calculations employed both standard and explicitly correlated coupled cluster techniques. All isomers possess C1 symmetry, with HOSCl being the most stable isomer. Only HOSCl and trigonal-HSOCl isomers are thermodynamically stable relative to the first dissociation limit HCl + SO. Fundamental modes of the lowest three isomers exhibit many anharmonic resonances, resulting in complex spectra. All isomers are found to be stable in the visible region as the calculation of vertical energy transition indicates. No electronic states were found to strongly absorb in the near UV–vis region. [ABSTRACT FROM AUTHOR]

The formation of the stable layer below about 2 x 106 Pa pressure level (about 20 km altitude) of the atmosphere of Venus detected by in situ observations is investigated by the use of a radiative-convective equilibrium model. We demonstrate that, assuming mixing ratio profiles of absorbers to be at the upper limits of the observed ranges for H2O and SO2 and the lower limit for CO, a stable layer forms as a radiative-convective equilibrium state, but its stability is lower than the observed one. Also, increasing the continuum absorption coefficient of CO2 and/or H2O, which are not well constrained observationally or experimentally, results in the formation of a stable layer whose stability is comparable to the observed one. These results suggest a practical method to form the stable layer in the dynamical models of the Venus atmosphere. Further, these results indicate that the important targets of future observations and laboratory measurements are to obtain more precise profiles of the mixing ratios of H2O, CO, and SO2 in the Venus atmosphere, and to determine the continuum absorption coefficients of those. [ABSTRACT FROM AUTHOR]

The current study explores the dynamic interaction between Interplanetary coronal mass ejections (ICMEs) and the induced magnetosphere of Venus, utilizing measurements from the Venus Express (VEX) mission. We have investigated 16 ICME events during the period 2006–2013. The altitude of the inbound bow shock and ionopause at Venus are comprehensively studied during the passage of these ICMEs. The ionosphere is found to be highly magnetized due to the very high magnetic pressure of the induced magnetosphere. Remarkably, the altitude of the ionopause is found to be significantly changed as compared to the previous quiet day due to the increased solar wind dynamic pressure Pdyn $\left({P}_{\mathit{dyn}}\right)$. The ratio of the altitude of ionopause and magnitude of the magnetic field (∣B∣) $(\vert B\vert)$ at ionopause on the event days to the quiet days shows a strong anti‐correlation which indicates the ionopause height is inversely related to the magnetic field. Intriguingly, the position of the bow shock exhibited minimal deviations compared to typical quiet days, underscoring that, during ICME events, the ionopause location is more responsive to solar wind pressure fluctuations than the bow shock location. Additionally, the heavy‐ion density near and above the ionopause is found to be significantly higher than that observed on previous quiet days. This substantial increase implies that ICMEs can induce atmospheric loss in Venus's atmosphere and also cause a significant reduction in the ionopause location. Key Points: The ionopause is found to be significantly changed during the passage of ICMEs compared to the quiet time valuesThe bow shock position exhibited minimal deviations during the event compared to typical quiet daysThe heavy‐ion density near and above the ionopause is significantly higher during ICMEs compared to previous quiet days [ABSTRACT FROM AUTHOR]

The article discusses several scientific studies published in the Proceedings of the National Academy of Sciences of the United States of America. One study examines the possibility of evolutionary rescue in a population of Magellanic penguins in Argentina, finding that the population has not undergone adaptive changes in body size over time. Another study analyzes the isotopic ratio of water vapor in the atmosphere of Venus, suggesting that condensation of sulfuric acid aerosols may explain the unexpected increase in the deuterium to hydrogen ratio. A computational model is used in a study on woody vine growth in forests, predicting that increases in CO2 and longer dry seasons could lead to an upsurge in liana infestation and a decrease in forest biomass. Lastly, a study on global agricultural greenhouse gas emissions finds that emission intensity has decreased globally over time, but has stagnated in recent years, highlighting the need for reductions in livestock production and improvements in global trade to mitigate emissions. [Extracted from the article]

The clouds have a great impact on Venus's energy budget and climate evolution, but its three‐dimensional structure is still not well understood. Here we incorporate a simple Venus cloud physics scheme into a flexible GCM to investigate the three‐dimensional cloud spatial variability. Our simulations show good agreement with observations in terms of the vertical profiles of clouds and H2SO4 vapor. H2O vapor is overestimated above the clouds due to efficient transport in the cloud region. The cloud top decreases as latitude increases, qualitatively consistent with Venus Express observations. The underlying mechanism is the combination of H2SO4 chemical production and meridional circulation. The mixing ratios of H2SO4 at 50–60 km and H2O vapors in the main cloud deck basically exhibit maxima around the equator, due to the effect of temperature's control on the saturation vapor mixing ratios of the two species. The cloud mass distribution is subject to both H2SO4 chemical production and dynamical transport and shows a pattern that peaks around the equator in the upper cloud while peaks at mid‐high latitudes in the middle cloud. At low latitudes, H2SO4 and H2O vapors, cloud mass loading and acidity show semidiurnal variations at different altitude ranges, which can be validated against future missions. Our model emphasizes the complexity of the Venus climate system and the great need for more observations and simulations to unravel its spatial variability and underlying atmospheric and/or geological processes. Plain Language Summary: On Venus, highly reflective clouds cover the surface entirely. This means that the clouds greatly impact Venus's current and, very likely, past energy budget. Therefore, understanding the Venus clouds is essential to constructing a full paradigm of the Venus climate and evolution. However, due to the lack of both three‐dimensional, long‐term observations and comprehensive climate models, the cloud spatial structure and its impact on atmospheric processes remain elusive. Here, we construct a three‐dimensional climate model that includes cloud physics and simple chemistry as the first step toward fully understanding the Venus clouds. Our simulated vertical profiles of the Venus clouds agree well with observations. We find that the condensable gases, sulfuric acid and water vapors in the cloud region become more abundant in the lower latitudes due to the temperature difference over different latitudes. The cloud top becomes lower as it approaches the polar region, and the underpinning processes are related to sulfuric acid chemical production and meridional circulation. The equatorial cloud structure shows semidiurnal features, which are related to the excited thermal tides in the Venus atmosphere. Our study is preparing for future Venus missions like EnVision, to maximize their science returns. Key Points: We construct a Venus climate model with cloud physics, and the cloud vertical structure agrees with observationsH2SO4 and H2O vapors in the middle cloud basically follow their SVMRs and show higher concentrations at low latitudesThe semidiurnal thermal tide affects H2SO4 and H2O vapors, cloud mass loading and acidity at different altitudes [ABSTRACT FROM AUTHOR]

The Venus atmosphere Superrotation (SR) is successfully simulated with the high‐resolution (1.25° × 1.25° in longitude and latitude) runs of the Venus Planetary Climate Model (PCM). The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 and 8.5 days. The simulation reproduces long‐term quasi‐periodic oscillation of the zonal wind and primary planetary‐scale wave seen in observations. These oscillations occur with a period of 163–222 days, although their existence is still debated in observations. The Rossby waves show similarity in wave characteristics and angular momentum (AM) transport due to Rossby‐Kelvin instability by comparing the 5.65‐day wave in Venus PCM with the 5.8‐day wave simulated by AFES‐Venus, another Venus General Circulation Model. Similarities are also evident between the 8.5‐day wave in Venus PCM and the 7‐day wave obtained in AFES‐Venus. The long‐term variations in the AM budget indicate that the 5.65‐day wave is the dominant factor of the oscillation on the SR, and the 8.5‐day wave plays a secondary role. When the 5.65‐day wave grows, its AM and heat transport are enhanced and accelerate (decelerate) the lower‐cloud equatorial jet (cloud‐top mid‐latitude jets). Meanwhile, the 8.5‐day wave weakens, reducing its deceleration effect on the lower‐cloud equator. This further suppresses the meridional gradient of the background wind and weakens instability, leading to the decay of the 5.65‐day wave. And vice versa when the 5.65‐day wave decays. Plain Language Summary: On Venus, large‐scale waves in the atmosphere play a crucial role in maintaining its fast westward‐moving atmosphere, known as superrotation (SR). Previous observations suggest that there might be long‐term variations in the SR. We simulated the Venusian SR using a high‐resolution atmospheric computer model to understand the mechanism behind this phenomenon. The simulation reproduced the variations in SR and the main large‐scale waves observed in reality. Among these waves, the one with a 5.65‐day period is the strongest wave in the upper clouds of Venus, in addition to the atmospheric thermal tides. In the simulations, the SR always varies with the changes in the 5.65‐day wave. This result indicates that the 5.65‐day wave significantly influences SR, possibly explaining the long‐term variations observed in SR. Key Points: Rossby‐Kelvin instability wave mode and their angular momentum (AM) transport to super‐rotation are robust in at least 2 Venus General Circulation ModelsLong‐term quasi‐periodic (163–222 days) variations in the superrotation and dominant wave simulated by Venus Planetary Climate Model are close to observationsDynamically conserved AM from circulation, 5.65‐day, and 8.5‐day waves drives quasi‐periodic variations of the local jets [ABSTRACT FROM AUTHOR]

This paper introduces the new Venus global ionosphere‐thermosphere model (V‐GITM) which incorporates the terrestrial GITM framework with Venus‐specific parameters, ion‐neutral chemistry, and radiative processes in order to simulate some of the observable features regarding the temperatures, composition, and dynamical structure of the Venus atmosphere from 70 to 170 km. Atmospheric processes are included based upon formulations used in previous Venus GCMs, several augmentations exist, such as improved horizontal and vertical momentum equations and tracking exothermic chemistry. Explicitly solving the momentum equations allows for the exploration of its dynamical effects on the day‐night structure. In addition, V‐GITM's use of exothermic chemistry instead of a strong heating efficiency accounts for the heating due to the solar EUV while producing comparable temperatures to empirical models. V‐GITM neutral temperatures and neutral‐ion densities are compared to upper atmosphere measurements obtained from Pioneer Venus and Venus Express. V‐GITM demonstrates asymmetric horizontal wind velocities through the cloud tops to the middle thermosphere and explains the mechanisms for sustaining the wind structure. In addition, V‐GITM produces reasonable dayside ion densities and shows that the neutral winds can carry the ions to the nightside via an experiment advecting O2+ ${\mathrm{O}}_{2}^{+}$. Plain Language Summary: We present a new, state‐of‐the‐art Venus global circulation model, the Venus global ionosphere thermosphere model. The new model will be useful for answering unknown questions about Venus' atmosphere, the physics of CO2 rich planets, and Venus missions utilizing the aerobraking maneuver. We performed many model simulations and compared the results to some of the existing Venus data sets to assess the accuracy of the model. The results showed that the dayside extreme ultraviolet heating can be captured using the dominant ion‐neutral chemistry rather than relying on simplified legacy methods. Furthermore, the cloud layer below the thermosphere has a unique wind pattern and its impact on the thermospheric temperatures and winds were explored. This work also revealed that the thin nightside ionosphere forms as a result of the transport of a single ion species. Key Points: A new, non‐hydrostatic Venus ionosphere‐thermosphere model is introduced with new physics not previously included in Venus GCMsSimulations during solar minimum conditions are used for data‐model comparisons of the temperatures, plasma, and neutral densitiesThe influence of the retrograde superrotating zonal flow is explored in relation to how it affects the neutral temperature and velocities [ABSTRACT FROM AUTHOR]

Sulfur–chlorine cycles play a role in the atmosphere of Venus. It is thought that many sulfur–chlorine bearing molecules could be present in Venus's atmosphere and play an important role in its chemical processes. The goal of this work is to provide new insight into the electronic structure and spectroscopy of the [Cl, S, S, O] molecular system. Eight isomers could be formed, but only three were found to be thermodynamically stable relative to the first dissociation limit. We spectroscopically characterized the two lowest energy stable isomers, C1–ClSSO and trans-ClSSO, using the accurate CCSD(T)-F12/aug-cc-pVTZ method. The dipole moments of the two lowest energy stable isomers are predicted to be 1.90 and 1.60 debye, respectively. The C1–ClSSO isomer is suitable for laser induced fluorescence detection since the lowest excited electronic states absorb in the visible, ∼610 nm, and near UV region, 330 nm. We mapped the evolution of the low-lying excited electronic states along the ClS, SS, and SO bond lengths to find that the production of ClS, SO, or S2O is plausible, whereas the production of ClS2 is not allowed. [ABSTRACT FROM AUTHOR]

The Venusian atmosphere hosts a 10 km deep convective layer that has been studied by various spacecrafts. However, the impact of the strong vertical mixing on the chemistry of this region is still unknown. This study presents the first realistic coupling between resolved small‐scale turbulence and a chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well‐mixed. Vertical eddy diffusion due to resolved convection motions was estimated, ranging from 102 to 104 m2/s for the 48–55 km convective layer, several orders of magnitude above the typically used value. In the 48–55 km convective layer, the impact of the small‐scale turbulence on the cloud layer boundaries was between 200 m and 1 km. The impact of turbulence on cloud chemistry is consistent with Venus Express/Visible and Infrared Thermal Imaging Spectrometer observations. The observability at the cloud‐top of small‐scale turbulence by VenSpec‐U spectrometer would be challenging. Plain Language Summary: Venus hosts a global sulfuric acid cloud layer between 45 and 70 km. A convective layer is present between roughly 50 and 60 km, with its variability in latitude and local time assessed by observation, with a thicker layer at high latitude and at night. One question that remains unclear is how this turbulence mixes momentum, heat, and chemical species. Especially, the impact of the strong vertical mixing on the chemistry of this region is still unknown. To investigate this topic, we use a convection‐resolving model coupled for the first time with a realistic chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well‐mixed. 1D and global circulation models use the so‐called vertical eddy diffusion approach to represent turbulent motion, quantified in our model and underestimated in chemistry models. The small‐scale turbulence in the cloud layer causes a variation in the altitude of the top and bottom boundaries of the cloud. Our model shows that the impact of turbulence on cloud chemistry corresponds well to what has been observed by satellites. In the future, the EnVision mission will be able to observe chemical species at the small turbulence scales. Key Points: Estimation for the first time of the spatial and temporal variability of chemical species due to vertical mixingQuantification of the vertical eddy diffusion coefficient, order of magnitude above typical used valuesCloud‐top altitudes change by 0.2–1 km due to vertical convective mixing and gravity waves [ABSTRACT FROM AUTHOR]

The collisionless nature of planetary magnetospheres means that electromagnetic forces are fundamental in controlling the flow of energy and momentum through these systems. We use Pioneer Venus Orbiter (PVO) observations to demonstrate that the magnetic pumping process can be active at Venus, in analogy to its recent discovery at Mars. The presented case study demonstrates the framework for how the process can work at Venus, and the results of a statistical analysis show that the ambient plasma conditions support the process being active. Magnetic pumping enables low frequency magnetosonic waves to heat ambient ionospheric electrons and provides a mechanism that couples the solar wind to the Venusian ionosphere. This is the first time the magnetic pumping process has been discussed at Venus. Plain Language Summary: Our Sun emits a stream of particles outward into our solar system, known as the solar wind. When these particles encounter planets and other bodies (such as comets), they either collide with the body (as happens with our Moon) or are deflected around the obstacle, similar to how water in a stream flows around a rock (this happens at most planets, including Earth, Venus and Mars). Understanding the physical forces that control this deflection enable us to understand how the Sun interacts with the planets in our solar system. We use in situ measurements made by the Pioneer Venus Orbiter spacecraft, which orbited the planet Venus, to investigate one specific process, known as "magnetic pumping." This process allows energy from the solar wind to flow into the Venusian atmosphere. We provide a case study demonstrating how this process can operate at Venus, and show that the average conditions in the near Venus space environment can support this process in a more general sense. Key Points: A case study demonstrates how the magnetic pumping process operates at VenusStatistical analysis of the plasma conditions at Venus support the notion that magnetic pumping can operate thereMagnetic pumping provides an avenue for the solar wind to couple to the Venusian ionosphere and heat ionospheric electrons [ABSTRACT FROM AUTHOR]

We use in situ plasma observations made by the Pioneer Venus Orbiter spacecraft to show for the first time that magnetosonic waves can couple the solar wind to the upper ionosphere and deposit energy there. The waves are generated upstream of Venus, are advected into the shock and propagate across the draped magnetic field, through the magnetosheath and into the dayside upper ionosphere. The magnetosonic waves damp in the upper ionosphere in a region where physical collisions are rare, and electromagnetic forces must control this damping. The waves damp when the ionospheric heavy ion density is a few thousand cm−3 and wave‐particle interactions with the dominant O+ ions are postulated as the damping mechanism. Estimates of ion heating rates show that 1%–5% of the O+ ion distribution function could be heated to escape energy in 10–40 s. Plain Language Summary: Our Sun emits a stream of charged particles radially outward into our Solar system, known as the solar wind. When the solar wind encounters obstacles such as planets and comets, a variety of forces may act to divert the flow around the obstacle, much like when flowing water in a stream encounters a rock and is diverted around it. This study uses measurements made by a spacecraft that orbited Venus, known as Pioneer Venus Orbiter, to investigate some of the side effects that can arise when the solar wind flow is diverted around Venus. We show for the first time how a particular pathway allows energy to be deposited from the flowing solar wind into the Venusian atmosphere, and that this energy can be deposited quickly enough to significantly impact the particles in the atmosphere. The characteristics observed in this study at Venus are similar to those at Mars where this process has also been observed, suggesting that the solar wind can interact with the two planets in similar ways in this respect. Key Points: Magnetosonic waves propagate from upstream into the dayside upper ionosphere of VenusMagnetosonic waves are damped by wave‐particle interactions with heavy ionospheric ionsSubsequent ion heating rates could heat 1%–5% of the ion distribution function to escape energy in 10–40 s [ABSTRACT FROM AUTHOR]

The document "Venus: Evolution Through Time" is a collection of papers that provide an overview of the evolution of Venus and its differences from Earth. The papers discuss various aspects of Venus, including its formation, composition, geodynamic state, tectonics, and volcanism. They also explore the history and characteristics of Venus' atmosphere, including the presence of volatiles and the possibility of past water on the planet's surface. The authors emphasize the need for further research and exploration, and highlight upcoming missions that will provide new data and insights into Venus' history and current activity. The document acknowledges the support received and the contributions of the reviewers. [Extracted from the article]

Exploring the Venusian lower atmosphere is crucial for studying the atmospheric circulation, surface‐atmosphere interactions, and origin and evolution of the Venusian atmosphere and climate. In this study, we investigate the theoretical capabilities of a downward‐looking passive microwave sounder placed in low Venus orbit to measure the temperature, sulfur dioxide (SO2) and gaseous sulfuric acid (H2SO4(g)) profiles. A nonlinear iterative retrieval algorithm combining a radiative transfer (RT) model and an optimal‐estimation‐based inversion algorithm is established. With the RT model adapted to the Venusian atmosphere, simulations under different atmospheric conditions are performed to optimize the selection of frequency channels. The achievable altitude coverage, vertical resolution and corresponding expected precision of the temperature, SO2 and H2SO4(g) retrievals from the multi‐channel brightness temperature measurements are quantified via retrieval simulations. The temperature can be retrieved from the surface of Venus to an altitude of ∼61 km with a precision of 1–3.5 K and a vertical resolution of 6–15 km. A precision of 10%–35% is expected for SO2 in the ∼12–64 km altitude range and with a vertical resolution of 8–19 km. H2SO4(g) can be retrieved in the ∼36–54 km altitude range with a precision of 10%–30% and a vertical resolution of 6–13 km. Plain Language Summary: The hostile environment and thick sulfuric acid clouds make it difficult to measure the lower atmosphere of Venus. Although many attempts have been made, the existing measurements of the lower atmosphere have provided little information about the spatiotemporal distribution and variation in the temperature and sulfur compound profiles. This limits our understanding of the atmospheric circulation, surface‐atmosphere interactions, and origin and evolution of the Venusian atmosphere and climate. In this study, we investigate the theoretical capabilities of a passive microwave sounder placed in low Venus orbit to measure the temperature, sulfur dioxide (SO2) and gaseous sulfuric acid (H2SO4(g)) profiles. By model simulations, the frequency channel selection and performance simulation for the sounder are completed. Simulation results demonstrate that the sounder could provide the required high‐precision, high‐resolution and vertically resolved observations of the temperature, SO2 and H2SO4(g) in the Venusian lower atmosphere. Key Points: The ability of a microwave radiometer to measure the temperature, SO2 and H2SO4(g) profiles in the Venusian lower atmosphere is verifiedThe measurement channels of the radiometer are determined based on radiative transfer simulationsThe expected precision, vertical resolution and achievable altitude coverage are quantified via retrieval simulations [ABSTRACT FROM AUTHOR]

Context. The CO2-dominated thick atmosphere of Venus coexists with an ionosphere that is mainly formed, on the dayside, via the ionization of atmospheric neutrals by solar extreme ultraviolet and soft X-ray photons. Despite extensive modeling efforts that have reproduced the electron distribution reasonably well, we note two main shortcomings with respect to prior studies. The effects of pro-tonation and Coulomb interaction are crucial to unveiling the structure and composition of the Venusian ionosphere. Aims. We evaluate the role of protonated species on the structure of the dayside Venusian ionosphere for the first time. We also evaluate the role of ion-ion Coulomb collisions, which are neglected in many existing models. Methods. Focusing on the solar minimum condition for which the effect of protonation is expected to be more prominent, we constructed a detailed one-dimensional photochemical model for the dayside Venusian ionosphere, incorporating more than 50 ion and neutral species (of which 17 are protonated species), along with the most thorough chemical network to date. We included both ion-neutral and ion-ion Coulomb collisions. Photoelectron impact processes were implemented with a two-stream kinetic model. Results. Our model reproduces the observed electron distribution reasonably well. The model indicates that protonation tends to diverge the ionization flow into more channels via a series of proton transfer reactions along the direction of low to high proton affinities for parent neutrals. In addition, the distribution of O2+ is enhanced by protonation by a factor of nearly 2 at high altitudes, where it is efficiently produced via the reaction between O and OH+. We find that Coulomb collisions influence the topside Venusian ionosphere not only directly by suppressing ion diffusion, but also indirectly by modifying ion chemistry. Two ion groups can be distinguished in terms of the effects of Coulomb collisions: one group preferentially produced at high altitudes and accumulated in the topside ionosphere, which is to be compared with another group that is preferentially produced at low altitudes and, instead, depleted in the topside ionosphere. Conclusions. Both protonation and Coulomb collisions have appreciable impacts on the topside Venusian ionosphere, which account for many of the significant differences in the model ion distribution between this study and early calculations. [ABSTRACT FROM AUTHOR]

As a fundamental physical process in the ionosphere, photoionization and the associated photoelectrons play vital roles in determining the ionospheric electron density and temperature for Earth and other planets with atmospheres such as Mars and Venus. The production and transport of ionospheric photoelectrons have been widely examined on Earth, but relatively less studied for other terrestrial planets, such as Mars and Venus. In this study, a two‐stream photoelectron transport model for Mars and Venus is constructed, in which the photoelectron fluxes, photoelectron heating rates, primary and secondary ionization rates are calculated. The simulated photoelectron fluxes agree with Mars Atmosphere and Volatile Evolution (MAVEN) observations at various altitudes, with the input of solar spectrum irradiance, electron density and temperature, neutral density and temperature observed by MAVEN. Moreover, by parametrically fitting the simulation results for various solar zenith angles and solar activities, we obtain empirical parameterized formulas for ionization and heating efficiencies which can potentially be adapted to planetary ionospheric models for the community. Key Points: A two‐stream model for Venus and Mars provides photoelectron flux, secondary ionization and photoelectron heating ratesThe photoelectron fluxes simulated by the two‐stream model agree with the Mars Atmosphere and Volatile Evolution observationsParameterized models of ionization and heating efficiencies are available for the community [ABSTRACT FROM AUTHOR]

The tentative detection of ppb levels of phosphine (PH[sub 3]) in the clouds of Venus was extremely surprising, as this reduced gas was not expected to be a component of Venus' oxidized atmosphere. Despite potential confirmation in legacy Pioneer Venus mass spectrometry data, the detection remains controversial. Here we review the potential production of phosphine by gas reactions, surface and sub-surface geochemistry, photochemistry, and other nonequilibrium processes. None of these potential phosphine production pathways is sufficient to explain the presence of phosphine in Venus atmosphere at near the observed abundance. The source of atmospheric PH[sub 3] could be unknown geo- or photochemistry, which would imply that the consensus on Venus' chemistry is significantly incomplete. An even more extreme possibility is that a strictly aerial microbial biosphere produces PH[sub 3]. The detection of phosphine adds to the complexity of chemical processes in the Venusian environment and motivates better quantitation of the gas phase chemistry of phosphorus species and in situ follow-up sampling missions to Venus. [ABSTRACT FROM AUTHOR]

This Letter reports the device and material investigations of enhancement-mode p-GaN-gate AlGaN/GaN high electron mobility transistors (HEMTs) for Venus exploration and other harsh environment applications. The GaN transistor in this work was subjected to prolonged exposure (11 days) in a simulated Venus environment (460 °C, 94 bar, complete chemical environment including CO2/N2/SO2). The mechanisms affecting the transistor performance and structural integrity in harsh environment were analyzed using a variety of experimental, simulation, and modeling techniques, including in situ electrical measurement (e.g., burn-in) and advanced microscopy (e.g., structural deformation). Through transistor, Transmission Line Method (TLM), and Hall-effect measurements vs temperature, it is revealed that the mobility decrease is the primary cause of reduction of on-state performance of this GaN transistor at high temperature. Material analysis of the device under test (DUT) confirmed the absence of foreign elements from the Venus atmosphere. No inter-diffusion of the elements (including the gate metal) was observed. The insights of this work are broadly applicable to the future design, fabrication, and deployment of robust III-N devices for harsh environment operation. [ABSTRACT FROM AUTHOR]

In this work, we focus on plasma discharges produced between two electrodes with a high potential difference, resulting in the ionization of the neutral particles supporting a current in a gaseous medium. At low currents and low temperatures, this process can create luminescent emissions: glow and corona discharges. The parallel plate geometry used in Townsend's theory lets us develop a theoretical formalism, with explicit solutions for the critical voltage effectively reproducing experimental Paschen curves. However, most discharge processes occur in non‐parallel plate geometries, such as discharges between particles in multiphase systems and between cylindrical conductors. Here, we propose a generalization of the classic parallel plate configurations to concentric spherical and coaxial cylindrical geometries in Earth, Mars, Titan, and Venus atmospheres. In a spherical case, a small radius effectively represents a sharp tip rod, while larger, centimeter‐scale radii represent blunted tips. In cylindrical geometries, small radii resemble thin wires. We solve continuity equations in the gap and estimate a critical radius and minimum breakdown voltage that allows the formation of a glow discharge. We show that glow coronæ form more easily in Mars's low‐pressure, CO2‐rich atmosphere than in Earth's high‐pressure, N2‐rich atmosphere. Additionally, we present breakdown criteria for Titan and Venus, two planets where discharge processes have been postulated. We further demonstrate that critical voltage minima occur at 0.5 cm⋅Torr for all three investigated geometries, suggesting easier initiation around millimeter‐size particles in dust and water clouds. This approach could be readily extended to examine other multiphase flows with inertial particles. Plain Language Summary: In this work, we focus on plasma discharges between two electrodes with a high voltage difference. The result is a conversion of the medium from an insulator to a conductor. At low currents and low temperatures, this process can create luminescent emissions: the so‐called glow and corona discharges. Here, we propose a generalization of Townsend's classic parallel plate configurations to concentric spheres and coaxial cylinders more likely to be encountered as particles in Earth, Mars, Venus, and Titan atmospheres. We computationally solve the continuity equations in the gap between objects and ultimately calculate critical electric fields for self‐sustained discharges. We show that glow coronæ form more easily in Mars's low‐pressure, carbon dioxide‐rich atmosphere than in Earth's high‐pressure, nitrogen‐rich atmosphere. Additionally, we present breakdown criteria for Titan and Venus. We further demonstrate that critical voltage minima occur near 0.5 cm ⋅ Torr for all three investigated geometries, suggesting easier initiation around millimeter‐size particles in dust and water clouds. Key Points: Numerical modeling lets us study glow coronæ around spherical and cylindrical electrodes based on Paschen theory in planetary atmospheresThe lowest requirements for discharge ignition occur at pressure×length‐scale products of 0.5 cm⋅Torr, independently of the geometryTownsend discharges are more easily ignited in low‐pressure and/or CO2‐rich atmosphere than in Earth's high‐pressure atmosphere [ABSTRACT FROM AUTHOR]

Recent ground-based observations of Venus have detected a single spectral feature consistent with phosphine (PH3) in the middle atmosphere, a gas which has been suggested as a biosignature on rocky planets. The presence of PH3 in the oxidized atmosphere of Venus has not yet been explained by any abiotic process. However, state-of-the-art experimental and theoretical research published in previous works demonstrated a photochemical origin of another potential biosignature—the hydride methane—from carbon dioxide over acidic mineral surfaces on Mars. The production of methane includes formation of the HC · O radical. Our density functional theory (DFT) calculations predict an energetically plausible reaction network leading to PH3, involving either HC · O or H· radicals. We suggest that, similarly to the photochemical formation of methane over acidic minerals already discussed for Mars, the origin of PH3 in Venus' atmosphere could be explained by radical chemistry starting with the reaction of ·PO with HC·O, the latter being produced by reduction of CO2 over acidic dust in upper atmospheric layers of Venus by ultraviolet radiation. HPO, H2P·O, and H3P·OH have been identified as key intermediate species in our model pathway for phosphine synthesis. [ABSTRACT FROM AUTHOR]

The recent and still controversial claim of phosphine detection in the venusian atmosphere has reignited consideration of whether microbial life might reside in its cloud layers. If microbial life were to exist within Venus' cloud deck, these microorganisms would have to be multi-extremophiles enclosed within the cloud aerosol particles. The most straightforward approach for resolving the question of their existence is to obtain samples of the cloud particles and analyze their interior. While developing technology has made sophisticated in situ analysis possible, more detailed information could be obtained by examining samples with instrumentation in dedicated ground-based facilities. Ultimately, therefore, Venus Cloud-level Sample Return Missions will likely be required to resolve the question of whether living organisms exist in the clouds of Venus. Two multiphase mission concepts are currently under development for combining in situ analyses with a sample return component. The Venus Life Finder architecture proposes collection of cloud particles in a compartment suspended from a balloon that floats for weeks at the desired altitude, while the Novel solUtion for Venus explOration and Lunar Exploitation (NUVOLE) concept involves a glider that cruises within the cloud deck for 1200 km collecting cloud aerosol particles through the key regions of interest. Both architectures propose a rocket-driven ascent with the acquired samples transported to a high venusian orbit as a prelude to returning to Earth or the Moon. Both future conceptual missions with their combined phases will contribute valuable information relative to the habitability of the clouds at Venus, but their fulfillment is decades away. We suggest that, in the meantime, a simplification of a glider cloud-level sample collection scenario could be accomplished in a shorter development time at a lower cost. Even if the cloud particles are not organic and show no evidence of living organisms, they would reveal critical insights about the natural history and evolution of Venus. [ABSTRACT FROM AUTHOR]

Long-standing unexplained Venus atmosphere observations and chemical anomalies point to unknown chemistry but also leave room for the possibility of life. The unexplained observations include several gases out of thermodynamic equilibrium (e.g., tens of ppm O2, the possible presence of PH3 and NH3, SO2 and H2O vertical abundance profiles), an unknown composition of large, lower cloud particles, and the "unknown absorber(s)." Here we first review relevant properties of the venusian atmosphere and then describe the atmospheric chemical anomalies and how they motivate future astrobiology missions to Venus. [ABSTRACT FROM AUTHOR]

This work reviews possible signatures and potential detectability of present-day volcanically emitted material in the atmosphere of Venus. We first discuss the expected composition of volcanic gases at present time, addressing how this is related to mantle composition and atmospheric pressure. Sulfur dioxide, often used as a marker of volcanic activity in Earth's atmosphere, has been observed since late 1970s to exhibit variability at the Venus' cloud tops at time scales from hours to decades; however, this variability may be associated with solely atmospheric processes. Water vapor is identified as a particularly valuable tracer for volcanic plumes because it can be mapped from orbit at three different tropospheric altitude ranges, and because of its apparent low background variability. We note that volcanic gas plumes could be either enhanced or depleted in water vapor compared to the background atmosphere, depending on magmatic volatile composition. Non-gaseous components of volcanic plumes, such as ash grains and/or cloud aerosol particles, are another investigation target of orbital and in situ measurements. We discuss expectations of in situ and remote measurements of volcanic plumes in the atmosphere with particular focus on the upcoming DAVINCI, EnVision and VERITAS missions, as well as possible future missions. [ABSTRACT FROM AUTHOR]

Venus' thick atmosphere is capable of destroying kilometer-sized bodies such as asteroids, creating various types of traces on the surface. While larger cosmic bodies are able to reach the surface, creating impact craters or crater dispersion fields, smaller bodies effectively transfer the initial kinetic energy into the atmosphere, resulting in an "atmospheric explosion" at some altitude. In these cases, the most visible marks on the surface of Venus are created by atmospheric shock waves and the flow of gas behind the shock fronts reflected from the solid surface. The transitional sizes of impactors that break up in the atmosphere but reach the surface give rise to clusters of craters. The paper presents the first results of three-dimensional calculations of the destruction of rocky asteroids in the atmosphere of Venus, indicating significant differences from simple two-dimensional axisymmetric calculations. [ABSTRACT FROM AUTHOR]

Barotropic, baroclinic, and Rossby‐Kelvin instabilities exist in the Venus atmosphere, as revealed by previous studies using numerical models. This study aims to deepen our understanding of the instabilities in the Venus atmosphere using the breeding of growing modes (BGM) method for the first time. We conducted a 1‐year model simulation as the control run. First, we conducted identical twin experiments in which random perturbations were added to the control run at the initial time, and they grew freely. Perturbations in the upper layer (UL, 70–100 km altitudes) grow faster at the beginning but saturate earlier at a low value compared to those in the lower layer (LL, 40–70 km altitudes). Next, we implemented the BGM method and conducted multiple breeding cycle experiments with different rescaling amplitudes and intervals, the two parameters of the BGM method. The bred vectors (BVs) from these experiments identified instabilities in various regions. With large rescaling amplitudes, the structure and amplitude of the BVs in the LL closely resembled the deviations in the control run, indicating the growth of BVs due to barotropic, baroclinic, and Rossby‐Kelvin instabilities. Composite mean analysis shows larger BV amplitudes in the morning hemisphere at the 60–70 km altitudes in the mid‐latitudes, indicating enhanced baroclinic instability by the thermal tide. Finally, we estimated the intrinsic predictability related to baroclinic instability for Venus is >1 month, which would be longer than that for the Earth of ∼2 weeks. Plain Language Summary: The Venus atmosphere has been studied by numerical models that take inputs such as temperature and winds and provide evolution. We applied the "breeding of growing mode" method to a numerical model to deepen our understanding of the dynamics of the Venus atmosphere. We use two independent model simulations starting with different inputs. When the differences become larger over time for some areas, it is a sign of instability in those areas. Instabilities can be studied by investigating how the differences change with time in various regions. We found that in the cloud layer at 40–70 km height, the difference grows slowly at the beginning. However, it becomes larger than the difference above the cloud layer at the 70–100 km height in the later stages, indicating that large‐scale instabilities dominate in the cloud layer while small‐scale instabilities dominate above. Additionally, we identified barotropic, baroclinic, and Rossby‐Kelvin instabilities at high, mid, and low latitudes in the cloud layer, respectively. Thermal tide due to solar heating impacts the instability around the cloud top (∼70 km) in the mid‐latitudes. Finally, the predictability of the Venus atmosphere would be longer for the Venus atmosphere (>1 month) than that for the Earth's atmosphere (∼2 weeks). Key Points: Identical twin experiments show that perturbations at 40–70 and 70–100 km altitudes are slow‐growing and fast‐growing modes, respectivelyBreeding cycle experiments generate perturbations associated with barotropic, baroclinic, and Rossby‐Kelvin instabilitiesThe intrinsic predictability related to the baroclinic instability is >1 month, longer than that for the Earth's atmosphere of ∼2 weeks [ABSTRACT FROM AUTHOR]

The spectroscopic detection of SO2 and unknown UV absorber substance in the H2SO4 cloud layer of Venus' atmosphere is currently a focal point in the study of the habitability of Venusian atmospheric clouds. This paper addresses the simultaneous detection requirements of multiple substances in the ultraviolet range of Venus' atmosphere and proposes a multi-channel hyperspectral imaging system design using pupil separation prisms and grating multilevel spectra. The system achieves a multi-channel design by splitting the entrance pupil of the telescope using prisms. Spectra from different channels are diffracted to the same detector through different orders of the grating. The system features a single spectrometer and detector, enabling simultaneous detection of spectra from different channels. It also boasts advantages such as compact size, ultra-high spectral resolution, and simultaneous multi-channel detection. The system design results indicate that within the working spectral range of three channels, the spectral resolution is better than 0.15 nm, surpassing previous in-orbit or current in-orbit planetary atmospheric detection spectrometers. With a Nyquist frequency of 56 lp/mm, the full-field MTF exceeds 0.7. The system's smile is less than 0.05 μm, and the keystone is less than 0.04 μm, meeting the requirements for imaging quality. [ABSTRACT FROM AUTHOR]

Planetary‐scale mountain waves have been observed at the cloud top of Venus and throughout the cloud deck. As they propagate from the surface to the cloud layers, multiple observations and numerical simulations have shown that they grow in size and do not break. However, the fate of mountain waves in the transition region and thermosphere, above the super‐rotating atmosphere, has only been addressed with two‐dimensional models. We conduct for the first time a simulation of mountain waves with a state‐of‐the‐art Venus climate model that includes the thermosphere. We find that mountain waves can propagate up to at least 150 km altitude, well above the transition region. They affect the circulation of the transition region, by reducing winds speeds, and the subsolar‐to‐antisolar circulation. Plain Language Summary: The planet Venus rotates very slowly, with a rotation period of 243 days, while its cloud cover rotates westwards much faster, with a period of 4 days at 70 km altitude, a phenomenon known as superrotation, which is not fully explained yet. Higher up, in the thermosphere, the air flows from the dayside to the nightside, rather than westwards. The thermosphere is difficult to explore by remote sounding due to the low air density, and thus its connection to the surface and the superrotating layer is poorly understood. In 2015, the Venus‐orbiting spacecraft Akatsuki detected a massive standing wave generated at the surface and reaching the superrotating layer, despite the fast zonal winds. Here, we show that this wave also reaches the thermosphere. Key Points: The first simulation of mountain waves with a 3D ground‐to‐thermosphere General Circulation Model is performedMountain waves reach the thermosphere of Venus and change the SS‐AS winds by up to 80 m/s, locally in the afternoonThe vertical wind field above the cloud deck is dominated by the effect of mountain waves [ABSTRACT FROM AUTHOR]

Venus was the first of the planets of the Solar System in the atmosphere of which electrical phenomena similar to lightning in the Earth's atmosphere were discovered. Electrical discharges (lightning in the atmosphere of Venus) were discovered in 1978 in the Venera-12, -11, and Pioneer Venus missions, based on their electromagnetic radiation. The paradox, however, was that the search for optical flares remained unsuccessful for the past 40 years. In 2015, the Akatsuki spacecraft of the Japan Aerospace Exploration Agency was launched into orbit Venus satellite. It was designed to search for lightning and other studies of the meteorology of Venus by recording radiation in selected spectral ranges. In 2016, the Akatsuki orbiter successfully performed detailed observations of Venus in the near-infrared range in the "transparency windows" of the planet's atmosphere, as well as in the ultraviolet and other ranges. The article presents the results of an alternative search for and successful detection of lightning flashes according to the Akatsuki project, but not in the ultraviolet or visible ranges, but in the near-IR range. A comparison of the results of calculations based on models of terrestrial lightning with the results of measurements made by the IR2 camera of the Akatsuki mission on Venus at a wavelength of 2.26 μm shows a close agreement between the experimental and calculated data. [ABSTRACT FROM AUTHOR]

The clouds of Venus are believed to be composed of sulfuric acid (H2SO4) and minor constituents including iron-bearing compounds, and their respective concentrations vary with height in the thick Venusian atmosphere. This study experimentally investigates possible iron-bearing mineral phases that are stable under the unique conditions within Venusian clouds. Our results demonstrate that ferric iron can react with sulfuric acid to form two mineral phases: rhomboclase [(H5O2)Fe(SO4)2·3H2O] and acid ferric sulfate [(H3O)Fe(SO4)2]. A combination of these two mineral phases and dissolved Fe3+ in varying concentrations of sulfuric acid are shown to be good candidates for explaining the 200-to 300-nm and 300-to 500-nm features of the reported unknown UV absorber. We, therefore, hypothesize a rich and largely unexplored heterogeneous chemistry in the cloud droplets of Venus that has a large effect on the optical properties of the clouds and the behavior of trace gas species throughout Venus's atmosphere. [ABSTRACT FROM AUTHOR]

Balloon-based exploratory platforms, or aerobots, are a budding planetary exploration technology for Venus to collect scientific data in-situ while keeping a safe distance from the highly inhospitable surface of Earth's "evil twin". Such a mission is expected to deploy and inflate the aerobot during the system's initial descent through the Venusian atmosphere, rather than launched from the surface. The analysis of the entry, descent and float (EDF) sequence of the aerobot is accordingly a delicate and fundamental part of the aerobot design, and generally where the envelope undergoes the largest loads. The inflation phase in particular plays an essential role, especially for variable-altitude aerobots that can have multiple-envelopes with different inflation requirements. This paper addresses a collection of preliminary considerations about the inflation phases of a Venus aerobot – starting from the end of deployment to completion of reaching an equilibrium altitude – where the nominal mission flight profile would then begin. We include two different inflation sequences, highlighting issues and threats, utilizing a simulation of the inflation dynamics of the aerobot conducted in MATLAB. The paper also presents results from a set of rapid inflation experiments, conducted on a subscale prototype of the aerobot, aimed at an initial assessment of feasibility and response of the materials involved. • Inflation sequence design for a variable-altitude aerobot at cloud-level on Venus. • Sequence modification to reduce peak loads on the aerobot. • Constraint-driven analysis to evaluate the impact of the model's initial parameters. • Laboratory demonstration of the inflation utilizing a subscale aerobot prototype. [ABSTRACT FROM AUTHOR]

Dependence of the radiative-convective equilibrium structure of the lower atmosphere of Venus on the specification of an atmospheric thermodynamic model is investigated. A series of thermodynamic models including ideal gases, van der Waals gases, and real gases are introduced by the use of the Helmholtz energy given by the EOS-CG mixture model (EOS-CG: Equation of State for Combustion Gases and Combustion Gas-like Mixtures). It is demonstrated that the radiative-convective equilibrium profile for the real gas differs significantly from that for the ideal gas with temperature-dependent specific heat by an increase of about 7 K in the surface temperature. This difference is caused by the fact that the adiabatic lapse rate evaluated with the thermodynamic model of real gas is larger than that of ideal gas, since the non-ideality of gas increases the thermal expansion coefficient, which overwhelms the increases in density and specific heat. It is confirmed that, in order to obtain better calculations of atmospheric circulations including the lower atmosphere of Venus, the ideal gas with a constant specific heat should be abandoned. The ideal gas with a temperature-dependent specific heat may not be enough. A promising method is to use the ideal gas but with the temperature-dependent specific heat such that its adiabatic lapse rate profile mimics that for the real gas. [ABSTRACT FROM AUTHOR]

Observations of young rapidly rotating G-type stars show that a large number of super-powerful flares occur on them. According to the early Sun activity model proposed by (Airapetian et al., 2016), it is assumed that during the first 700 million years there were 250 flares per day with an energy release comparable to the Carrington event of 1859. Within the framework of this model, the high intensity of irradiation of the Earth's atmosphere by solar cosmic rays (SCR) led to the formation of a large amount of greenhouse gases in ion-molecular reactions. Their high concentration in the atmosphere of the early Earth made it possible to solve the so-called "early Sun" paradox, where high climate temperatures existed on Earth at a reduced luminosity (by 20–30%). We have estimated the possible parameters of early Sun activity from data on the isotope composition of gases in the atmospheres of terrestrial planets. As a result of nuclear reactions of SCR protons with atmospheric gases, the 13C/12C and 15N/14N isotope ratios increase in the atmospheres of planets, since the yields of heavy and light C and N isotopes in nuclear spallation reactions are close, and the initial 13C/12C and 15N/14N ratios in planetary atmospheres are less than 0.01. The production of isotopes depends on the shape of the proton spectrum, the intensity of SCR fluxes, and the composition of early atmospheres. Therefore, modern 13C/12C and 15N/14N isotope ratios in the atmospheres of Venus and Mars give a limit to the activity of the early Sun. Our calculations show that in the Martian atmosphere the 13C/12C ratio should increase by tens of percent, and 15N/14N by several times, which contradicts the measurements. In the atmosphere of Venus, the change in isotope ratios under the influence of SCR is within the limits of the measurement error. Possible explanations of the obtained results are considered, including restrictions on the level of activity of the early Sun and SCR spectra, and the possible composition and mass of the early atmospheres of Mars and Venus. [ABSTRACT FROM AUTHOR]

In an attempt to understand the findings presented in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), we followed their data analysis methodology, omitting the hot and cold‐load calibrations that are an important part of the standard SOFIA GREAT instrument calibration procedure. This process requires scaling of the Venus off‐source spectra by an arbitrary factor, which in turn introduces residuals of the intrinsic receiver bandpass shape as spurious components in the resulting line/continuum spectra. Although these additional artifacts can be reduced via Fourier‐domain spectral filtering, their removal depends on an ill‐constrained interpolation of the Venus continuum across the PH3 spectral line positions, resulting in an unreliable final spectrum. We therefore conclude that the PH3 lines claimed to be detected in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) originate from data/analysis artifacts, and confirm our original result that there is no evidence for phosphine in the SOFIA Venus data. Plain Language Summary: We performed observations using a unique, flying telescope—the Stratospheric Observatory for Infrared Astronomy (SOFIA)—to search for a gas called phosphine in the atmosphere of Venus, which has been suggested to be an indicator for life. The observations, published by Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055), were analyzed carefully but showed no evidence of phosphine. Our findings were called into question in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), who claimed to find phosphine lines in the SOFIA observations after following an unconventional data analysis method. We have investigated their method, and conclude that it is likely to introduce spurious signals into the data, so the claimed phosphine detection is therefore not significant. Key Points: The revised calibration procedure adopted by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) introduces additional receiver artifacts into the SOFIA 4G2 Venus spectraThe claimed PH3 detection is likely a result of this, combined with interpolation artifacts that occur during subsequent Fourier filteringWe confirm our original conclusion that there is no evidence for phosphine in the SOFIA GREAT Venus data [ABSTRACT FROM AUTHOR]

Searches for phosphine in Venus' atmosphere have sparked a debate. Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055) analyze spectra from the Stratospheric Observatory For Infrared Astronomy (SOFIA) and infer <0.8 ppb of PH3. We noticed that some spectral artifacts arose from non‐essential calibration‐load signals. By‐passing these signals allows simpler post‐processing and a 5.7σ candidate detection, suggesting ∼3 ppb of PH3 above the clouds. Compiling six phosphine results hints at an inverted abundance trend: decreasing above the clouds but rising again in the mesosphere from some unexplained source. However, no such extra source is needed if phosphine is undergoing destruction by sunlight (photolysis), to a similar degree as on Earth. Low phosphine values/limits are found where the viewed part of the super‐rotating Venusian atmosphere had passed through sunlight, while high values are from views moving into sunlight. We suggest Venusian phosphine is indeed present, and so merits further work on models of its origins. Plain Language Summary: Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055) find no phosphine in Venus' atmosphere, using the airborne SOFIA telescope. By‐passing some instrumental effects, we extract a detection with 5.7σ‐confidence from the same data. We can resolve the tension between high and low PH3 abundance values by noticing that the former are from "mornings" in Venus' atmosphere and the latter from "evenings." Sunlight reduces the amount of phosphine in Earth's atmosphere by an order of magnitude, so similarly on Venus, we might expect lower abundances in data taken when the part of the atmosphere observed has passed through sunlight. If the six available data sets can be reconciled in this way, further modeling of possible sources of PH3 (e.g., volcanic, disequilibrium chemistry, extant life) seem worthwhile. Key Points: We recover Venusian phosphine in SOFIA spectra by reducing contaminating signals; the PH3 abundance is ∼3 part‐per billion (ppb)Six recoveries/limits show PH3 depleting between clouds and mesosphere, which would require an unknown re‐formation process or extra sourceRecoveries and upper limits can instead be reconciled by PH3 photolysis, as high/low abundances correspond to Venusian mornings/evenings [ABSTRACT FROM AUTHOR]

Studies of the Venusian mesosphere provide important information about the current state of the entire Venusian atmosphere. This includes information about the dense cloud structure, its vertical thermal profile, temperature fields, and the resulting dynamical and meteorological processes that contribute to a deeper understanding of the climatologically different evolutionary paths of Earth and Venus. However, the last measurements were acquired in 1983 during Venera-15 mission. In this paper, results of mid-infrared spectral measurements of the Venusian atmosphere are presented. Here we show Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) measurements of the Venusian atmosphere during the second flyby of BepiColombo mission on its way to Mercury. Our Venus measurements provide reliable retrievals of mesospheric temperature profiles and cloud parameters between 60 and 75 km altitude, although MERTIS was only designed to operate in Mercury environment. Our results are in good agreement with the Venera-15 mission findings. This indicates the stability of the Venusian atmosphere on time scales of decades. On its way to Mercury, BepiColombo spacecraft made two flybys of Venus. Here, the authors show spectrally resolved measurements of Venus' atmosphere during BepiColombo's second flyby and reveal that Venusian atmosphere has been stable since 1980s. [ABSTRACT FROM AUTHOR]

This review presents an insight into our current knowledge of the atmospheres of the planets Venus, Mars, Jupiter, Saturn, Uranus and Neptune, the satellite Titan, and those of exoplanets. It deals with the thermal structure, aerosol properties (hazes and clouds, dust in the case of Mars), chemical composition, global winds, and selected dynamical phenomena in these objects. Our understanding of atmospheres is greatly benefitting from the discovery in the last 3 decades of thousands of exoplanets. The exoplanet properties span a broad range of conditions, and it is fair to expect as much variety for their atmospheres. This complexity is driving unprecedented investigations of the atmospheres, where those of the solar systems bodies are the obvious reference. We are witnessing a significant transfer of knowledge in both directions between the investigations dedicated to Solar System and exoplanet atmospheres, and there are reasons to think that this exchange will intensity in the future. We identify and select a list of research subjects that can be conducted at optical and infrared wavelengths with future and currently available ground-based and space-based telescopes, but excluding those from the space missions to solar system bodies. [ABSTRACT FROM AUTHOR]

Despite Venus having insignificant intrinsic magnetic fields, the magnetic connectivity between the solar wind and the Venus ionosphere, or magnetic topology, is not as simple as expected and is also important for characterizing the Venus space environment. This study provides a technique combining superthermal electron energy and pitch angle distributions to infer up to 6 subtypes of magnetic topology at Venus. This enables us to determine magnetic topology with automated procedures using the Venus Express (VEx) observations from May 2006 to November 2014. We find that the draped topology (both ends of a field line not connected to the collisional ionosphere) is the dominant topology in the near‐Venus space environment, >70%, except at low altitudes close to the ionosphere. The open (a field line connected to both the solar wind and the collisional ionosphere) and closed (a field line connected only to the collisional ionosphere) topologies make up 20%–30% on average of the magnetotail and up to 50% at low altitudes. This study provides the first characterization of the statistical distributions of different magnetic topologies at Venus. Plain Language Summary: Venus has insignificant intrinsic magnetic fields and its magnetic environment consists of the solar magnetic field lines draping around the planet, or the so‐called induced magnetosphere. However, some of the draping magnetic fields could penetrate deeply into the Venus collisional atmosphere, producing complex magnetic connectivities in the near Venus space environment. This study provides a technique to determine the magnetic connectivity with automated procedures by using electron and magnetic field measurements obtained from the Venus Express (VEx) mission from May 2006 to November 2014. The statistical distributions of different magnetic connectivities at Venus are characterized for the first time. The findings of this study further our understanding of the Venus magnetosphere. Key Points: This study provides a technique combining superthermal electron energy and pitch angle distributions to infer magnetic topology at VenusThe statistical distributions of different magnetic topologies at Venus are characterized for the first timeThe closed and open topologies have high occurrence rates at low altitudes while the draped topology dominates other regions [ABSTRACT FROM AUTHOR]

This study evaluates the high-temperature stability of soft magnetic materials under expected Venusian surface conditions to inform relevant lander designs. Soft magnetic materials enable motors, actuators, and passive components in the power conversion system. We investigate two common bulk crystalline alloys, Fe81Cr19 and Fe49Co49V2, as well as a metallic glass, Co72Fe4Mn4Nb4Si2B14. Pertinent atmospheric conditions were simulated using the NASA Glenn Extreme Environment Rig (GEER). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were performed on exposed samples leading to further understanding of the corrosion behavior of Fe- and Co-based materials in a simulated Venusian atmosphere. Both oxidation and sulfidation are induced in all three materials. The amorphous structure of Co72Fe4Mn4Nb4Si2B14 and, potentially, the formation of B and Si-based protective layers, yield improved corrosion resistance relative to Fe49Co49V2. [ABSTRACT FROM AUTHOR]

The conditions in Venus' upper mesosphere at around 120 km have some similarities to the upper mesosphere of Earth and Mars where ice clouds form. Here we show, using published satellite products and numerical modeling, that the upper mesosphere of Venus can be sufficiently cold that both H2O and CO2 may condense to form particles. We show that amorphous solid water particles (ASW) are likely to nucleate both heterogeneously on meteoric smoke and also homogeneously, resulting in clouds of nano‐scaled particles at around 120 km that will occur globally. The temperatures may then become sufficiently low, below ∼90 K, that CO2 particles can nucleate on ASW particles. Given the uncertainty associated with retrievals of temperature in the upper mesosphere, it is unclear how frequently this occurs, but it could be >30% of the time poleward of 60°. Since the main component of Venus' tenuous atmosphere is CO2, any CO2 crystals that form will grow and sediment on a timescale of 10–20 min. Mie calculations show that these Venusian mesospheric clouds (VMCs) should be observable by contemporary satellite instruments, although their short lifetime means that the probability of detection is small. We suggest that VMCs are important for the redistribution of meteoric smoke and may serve as a cold‐trap, removing some water vapor from the very upper mesosphere of Venus through the growth and sedimentation of cloud particles, and possibly reducing the loss of water to space. Plain Language Summary: Venus is renowned for extreme heat at the surface and clouds composed of sulfuric acid encircling the planet; however, there are regions of Venus's atmosphere that are sufficiently cold to harbor ice clouds. In fact, the temperatures frequently fall below 100 K at around 120 km altitude and under the right conditions, we have shown that ice clouds composed of both water and carbon dioxide ices can form. We have used published data from satellites that orbit Venus to show that clouds composed of nanometer sized water ice particles may encircle the planet. The temperatures are so low in this part of Venus' atmosphere that the ice in these water ice particles likely lacks any crystalline structure, i.e., it has an amorphous (liquid‐like) structure. Furthermore, if the temperature falls below about 90 K, we have shown that carbon dioxide ice crystals can form on top of water ice particles. Since the atmosphere of Venus is mainly made of carbon dioxide, these carbon dioxide crystals grow and then sediment rapidly in the thin atmosphere. If we were lucky enough to see one of these short‐lived sporadic clouds, it would look a bit like mares' tail cloud on Earth. Key Points: The upper mesosphere of Venus can be supersaturated with respect to both amorphous solid water (ASW) and crystalline carbon dioxide iceThere is a persistent layer of nano‐scale ASW particles encircling VenusShort‐lived carbon dioxide ice clouds may sporadically form in the upper mesosphere [ABSTRACT FROM AUTHOR]

We develop a new model of diffusively modulated hydrodynamic escape to predict oxygen isotopic fractionations caused by the loss of water from a steam atmosphere of Venus. The chief technical advance over previous work is including CO 2 as a major species. We find that ordinary (δ 18 O) and mass-independent (Δ 17 O) fractionations depend mostly on the extent of lithospheric buffering and the ferocity of EUV heating when escape took place, and relatively little on the size of the lost ocean(s). It is likely that Δ 17 O evolved significantly from its birth state, not only in the atmosphere but also in the silicates of the crust and upper mantle. If both δ 18 O and Δ 17 O of Venus are identical to Earth and Moon, we may conclude that Venus and Earth accreted from a common pool. But differences in δ 18 O and Δ 17 O can be attributed to escape rather than to genetics. If the differences are large enough, they can be used to constrain when escape took place and the extent of volatile exchange with the lithosphere. Neon and argon systematics are most consistent with minimal escape, especially if an Ar-rich source, possibly derived from comets, is added. However, we also find a novel class of solutions in which Ne and Ar of Venus, Earth, and Mars are evolved from a common source material subject to different vigors of hydrodynamic escape, least extreme for Earth and most extreme for Mars. These alternative models require that Venus was always rather dry (<10% of an Earth ocean) and its water lost very early (before <100 Myrs). The two styles of escape – minimal or extreme – should be readily distinguished by an unambiguous measurement of the Ar/Kr ratio. Finally, we find that predicted D/H enrichments are of order 100 for almost all model parameters. This result, a direct consequence of diffusion-limited escape of H and D, provides support for the overall scenario. • Oxygen isotopes can be strongly fractionated by hydrodynamic escape. • There can be no expectation that Venus retains an interpretable record of its birth composition in its oxygen isotopes. • Diffusion-limited hydrogen escape correctly predicts D/H fractionation on Venus. • We develop a novel explanation of Ne/Ar systematics that can encompass Venus, Earth, Mars, and chondrites. [ABSTRACT FROM AUTHOR]

Atomic oxygen is a key species in the mesosphere and thermosphere of Venus. It peaks in the transition region between the two dominant atmospheric circulation patterns, the retrograde super-rotating zonal flow below 70 km and the subsolar to antisolar flow above 120 km altitude. However, past and current detection methods are indirect and based on measurements of other molecules in combination with photochemical models. Here, we show direct detection of atomic oxygen on the dayside as well as on the nightside of Venus by measuring its ground-state transition at 4.74 THz (63.2 µm). The atomic oxygen is concentrated at altitudes around 100 km with a maximum column density on the dayside where it is generated by photolysis of carbon dioxide and carbon monoxide. This method enables detailed investigations of the Venusian atmosphere in the region between the two atmospheric circulation patterns in support of future space missions to Venus. Atomic oxygen is important for the photochemistry and energy balance of Venus's atmosphere, but it was not directly observed on the dayside of Venus. Here, the authors show direct detection of atomic oxygen on the both dayside and nightside of Venus by measuring its ground-state transition at 4.74 THz. [ABSTRACT FROM AUTHOR]

The origin of life and the detection of alien life have historically been treated as separate scientific research problems. However, they are not strictly independent. Here, we discuss the need for a better integration of the sciences of life detection and origins of life. Framing these dual problems within the formalism of Bayesian hypothesis testing, we demonstrate via simple examples how high confidence in life detection claims require either (1) a strong prior hypothesis about the existence of life in a particular alien environment, or conversely, (2) signatures of life that are not susceptible to false positives. As a case study, we discuss the role of priors and hypothesis testing in recent results reporting potential detection of life in the venusian atmosphere and in the icy plumes of Enceladus. While many current leading biosignature candidates are subject to false positives because they are not definitive of life, our analyses demonstrate why it is necessary to shift focus to candidate signatures that are definitive. This indicates a necessity to develop methods that lack substantial false positives, by using observables for life that rely on prior hypotheses with strong theoretical and empirical support in identifying defining features of life. Abstract theories developed in pursuit of understanding universal features of life are more likely to be definitive and to apply to life-as-we-don't-know-it. We discuss Molecular Assembly theory as an example of such an observable which is applicable to life detection within the solar system. In the absence of alien examples these are best validated in origin of life experiments, substantiating the need for better integration between origins of life and biosignature science research communities. This leads to a conclusion that extraordinary claims in astrobiology (e.g., definitive detection of alien life) require extraordinary explanations, whereas the evidence itself could be quite ordinary. [ABSTRACT FROM AUTHOR]

The equatorial jet in the Venusian lower cloud layer (47–55 km altitudes) and its quasi‐periodic variation are found in a general circulation model (GCM). The equatorial jet is produced by the 5.8‐day wave and destroyed by the 7‐day wave, and its quasi‐periodic variation with a timescale of about 280 days is caused by the alternating development of these waves in the GCM. The 5.8‐day wave, which is excited by the Rossby‐Kelvin instability, produces the equatorward angular momentum (AM) flux, and accelerates the zonal‐mean zonal wind in the equatorial region. The 7‐day wave, newly found in the present study, is a planetary‐scale wave antisymmetric about the equator, although it has not yet been observed. It is excited by the coupling among the lower‐altitude equatorial Rossby mode, the mid‐latitude Rossby mode, and the high‐latitude Rossby mode. In the growth period, the 7‐day wave produces the poleward (equatorward) AM flux around the equatorward (poleward) critical latitude. As a result, the zonal‐mean zonal wind is decelerated (accelerated) in the equatorial region and high latitudes (mid‐latitudes). In the regrowth period, the lower‐altitude equatorial Rossby mode disappears due to the disappearance of the equatorial jet, but the high‐latitude Rossby mode is still enhanced by the coupling with the mid‐latitude Rossby mode. These results could provide a possible explanation of the equatorial jet inferred from the recent Akatsuki observation, although it should be investigated by further observations. Plain Language Summary: Recent observations by the infrared camera onboard Akatsuki showed a possibility that the equatorial jet, which is a narrow band of zonal (east‐west) winds with a maximum rotational speed near the equator, could exist in altitudes of 47–55 km in the Venusian atmosphere and vary significantly in time. We reproduced this equatorial jet and its quasi‐periodic variation in a general circulation model. The equatorial jet is produced by the equatorward angular momentum (AM) transport due to the 5.8‐day wave and destroyed by the poleward AM transport due to the 7‐day wave. The 5.8‐day wave, which is excited by the Rossby‐Kelvin instability, corresponds to the 5‐day wave observed around 70 km altitude. The 7‐day wave is a planetary‐scale wave newly found in the present study, although it has not yet been observed in previous observations. The quasi‐periodic variation of the equatorial jet is caused by the alternating development of these waves in the model. The present result provides a possible explanation of the equatorial jet inferred from the Akatsuki observation. Key Points: Equatorial jet in the Venusian lower cloud layer could be produced by the 5.8‐day wave and destroyed by the 7‐day waveQuasi‐periodic variations of the equatorial jet could be caused by the alternating development of 5.8‐day and 7‐day wavesThe 7‐day wave, which has not yet been observed, is a planetary‐scale wave excited by the coupling among three Rossby modes [ABSTRACT FROM AUTHOR]

In recent years atomic oxygen (AO) has become a major challenge for the space community. AO is the most dominant species of the residual atmosphere in low Earth orbit (LEO). In addition, AO was found at the top of the Venusian and Martian atmospheres. As a result of exposure to AO, organic space-facing materials erode, leading to changes in their roughness, thermo-optical properties, and mass loss. In the past years, there has been a growing interest in very low Earth orbit missions, below an altitude of 350 km, where AO density and thus, AO flux, are extremely high. At these low altitudes, material degradation by AO erosion poses a great risk to the integrity of any space-facing material, unless well protected. As such, measuring the AO flux and the consequential material erosion by AO, in real-time while under actual space conditions, are of great interest to the space community. Thus, in this work we present real-time AO material erosion measurements that were conducted, for the first-time in LEO, using the on-orbit material degradation detector (ORMADD). The ORMADD is a low-cost and simple to operate detector, comprised of photovoltaic cells coated with semi-transparent AO sensitive coatings. Two ORMADDs were integrated on TAUSAT-1, a 3U CubeSat, deployed into LEO from the international space station. The first ORMADD was coated with a thin amorphous-carbon coating and the second was covered with a thick pyrolytic Kapton film. Using ORMADD, we were able to follow the erosion of the coatings in real-time conditions and calculate the AO flux in TAUSAT-1 orbit. The average in-orbit flux, derived from ORMADD data, was found to be comparable to the theoretical average AO flux calculated by the space environment information system (SPENVIS) software. This work demonstrates the abilities of ORMADD as a space environment detector, as well as a space material degradation research instrument. • Atomic oxygen measurements were done by the on-orbit material degradation detector. • The on-orbit material degradation detector is based on coated photovoltaic cells. • The erosion of the coating was measured and the atomic oxygen flux was derived. • Atomic oxygen flux was also simulated by the SPENVIS simulation software. • Space measured atomic oxygen flux is comparable to the flux simulated by SPENVIS. [ABSTRACT FROM AUTHOR]

Despite great interest by the planetary science community in the robotic exploration of Venus, solutions for operating in this extreme environment present significant challenges to mission architects. A particular challenge in designing any in situ Venus mission of reasonable duration is the selection of a suitable power source. State-of-the-art space power technologies comprising solar arrays, batteries and radioisotope thermoelectric generators are not capable of operating on the surface of Venus, limited by the high temperatures, high pressures and corrosive environment. Despite its proximity to the Sun, the solar resource on the surface is limited by the dense cloud layers. One potential approach for circumventing this limitation includes collecting the abundant visible solar energy above the Venus atmosphere, and wirelessly transferring this power to the surface at a wavelength that can more effectively penetrate the dense cloud layer. The feasibility of such an approach and other related mission concepts are discussed herein from a perspective of atmospheric absorption and scattering of the beamed energy. • A lack of suitable power source options limits the feasibility of long duration Venus surface missions. • Collection of the significant solar resource at the top of the Venus atmosphere using solar arrays coupled with wireless transfer of this harvested energy to the surface is not feasible, due to significant attenuation of electromagnetic energy at both microwave and optical/infrared wavelengths. • Optical windows do exist in portions of the Venus atmosphere, whereby a fraction of harvested energy could be transmitted via a laser power source to a laser power converter on the surface. • To implement such an optical power beaming scheme would require the use of an atmospheric platform, such as a variable altitude balloon, which could harvest the solar energy at a height of approximately 47 km and then transmit this to the surface at a wavelength aligned with these optical windows. [ABSTRACT FROM AUTHOR]

The current state and surface conditions of the Earth and its twin planet Venus are drastically different. Whether these differences are directly inherited from the earliest stages of planetary evolution, when the interior was molten, or arose later during the long-term evolution is still unclear. Yet, it is clear that water, its abundance, state, and distribution between the different planetary reservoirs, which are intimately related to the solidification and outgassing of the early magma ocean, are key components regarding past and present-day habitability, planetary evolution, and the different pathways leading to various surface conditions. In this chapter we start by reviewing the outcomes of the accretion sequence, with particular emphasis on the sources and timing of water delivery in light of available constraints, and the initial thermal state of Venus at the end of the main accretion. Then, we detail the processes at play during the early thermo-chemical evolution of molten terrestrial planets, and how they can affect the abundance and distribution of water within the different planetary reservoirs. Namely, we focus on the magma ocean cooling, solidification, and concurrent formation of the outgassed atmosphere. Accounting for the possible range of parameters for early Venus and based on the mechanisms and feedbacks described, we provide an overview of the likely evolutionary pathways leading to diverse surface conditions, from a temperate to a hellish early Venus. The implications of the resulting surface conditions and habitability are discussed in the context of the subsequent long-term interior and atmospheric evolution. Future research directions and observations are proposed to constrain the different scenarios in order to reconcile Venus' early evolution with its current state, while deciphering which path it followed. [ABSTRACT FROM AUTHOR]

In this work we discuss various selected mission concepts addressing Venus evolution through time. More specifically, we address investigations and payload instrument concepts supporting scientific goals and open questions presented in the companion articles of this volume. Also included are their related investigations (observations & modeling) and discussion of which measurements and future data products are needed to better constrain Venus' atmosphere, climate, surface, interior and habitability evolution through time. A new fleet of Venus missions has been selected, and new mission concepts will continue to be considered for future selections. Missions under development include radar-equipped ESA-led EnVision M5 orbiter mission (European Space Agency 2021), NASA-JPL's VERITAS orbiter mission (Smrekar et al. 2022a), NASA-GSFC's DAVINCI entry probe/flyby mission (Garvin et al. 2022a). The data acquired with the VERITAS, DAVINCI, and EnVision from the end of this decade will fundamentally improve our understanding of the planet's long term history, current activity and evolutionary path. We further describe future mission concepts and measurements beyond the current framework of selected missions, as well as the synergies between these mission concepts, ground-based and space-based observatories and facilities, laboratory measurements, and future algorithmic or modeling activities that pave the way for the development of a Venus program that extends into the 2040s (Wilson et al. 2022). [ABSTRACT FROM AUTHOR]