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Parker Solar Probe (PSP) uses Venus gravity assists (VGA) to achieve the closest orbits to the Sun by a spacecraft. During the third (VGA3) and fourth (VGA4) Venus gravity assists, the PSP entered the Venusian ionosphere. The core electrons could not be detected as they were below the SWEAP/SPAN electrostatic analyzer instrument energy threshold. However, there is another way to estimate the core temperature using quasi‐thermal noise (QTN) data measured by the PSP/FIELDS Radio Frequency Spectrometer instrument. QTN spectroscopy offers an effective tool for measuring electron temperature and density when the electrons are too cold for other instruments to measure, as is the case with VGA3 and VGA4. Low‐frequency plasma wave data from the closest approach during VGA3 and VGA4 was analyzed with the QTN spectroscopy technique to determine the density and first‐ever in‐situ thermal electron temperature of the Venusian ionosphere at solar minimum. Plain Language Summary: Parker Solar Probe is a NASA mission designed to collect solar wind data closer to the Sun than any spacecraft has before. It uses Venus' gravity to achieve its close orbit, collecting data at Venus while doing so. Quasi‐thermal noise spectroscopy was used to determine the thermal electron properties of the Venusian ionosphere during these gravity assists when other instruments could not. This analysis provides insights into how Venus' ionosphere reacts to the solar cycle and how the ionosphere is losing mass. Key Points: Thermal electron properties of Venus' ionosphere can be determined using quasi‐thermal noise spectroscopyVenusian ionospheric electron temperatures are found to be colder at solar minimum than maximumAmbipolar fields, not wave heating, may be the main source of outfield flow in Venusian tail rays [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]

Venus preserves ∼1,000 impact craters, yet to date no impact basins larger than 300 km in diameter—common in the oldest terrains on Mercury, Mars and the Moon—are recognized on Venus. The tessera terrain is Venus' oldest recognized terrain. We describe a ∼1,500 km‐diameter concentric ring‐graben complex preserved on Haasttse‐baad Tessera, Venus that we identify as the Haasttse‐baad Tessera Ring Complex (HTRC). Based on geologic relations and numerical modeling, we propose that the HTRC may represent a Valhalla‐type multiring impact basin formed late during the evolution of its host ribbon‐tessera terrain (rtt). Formation of Valhalla‐type impact basins could involve a unique three‐layer target rheology with a thin elastic layer above a low viscosity layer above a deep strong layer. This multi‐layer rheological sandwich is consistent with crustal rheology previously proposed for the formation of Venus' rtt. If the HTRC is a Valhalla‐type impact basin, it would be Venus' oldest, and currently largest, impact structure, providing a rare window into Venus' ancient past and with implications for early crustal processes on Venus. Plain Language Summary: Venus preserves ∼1,000 impact craters, but no craters larger than 300 km—common on Mercury, Mars, and Moon—are recognized. We describe a large circular structure (∼1,500 km‐diameter) that formed on tessera terrain, Venus' oldest recognized surface type. The structure consists of concentric circular troughs that cut the tessera surface; geologic mapping shows that the structure formed late during tessera formation. We discuss the different mechanisms for forming large circular features marked by concentric rings of structures, and propose that it could be an example of a large impact basin named Valhalla‐type impact basin after a structure present in Jupiter's moon Callisto. Previous research suggests that the formation of these impact basins likely involves a distinctive layering in the impact site consisting of a sandwich of layers with different strengths (strong‐weak‐strong), a configuration previously proposed as necessary to form the host tessera terrain. Numerical models show that forming the circular structure as a Valhalla‐type impact basin is possible if a large meteorite crashes into this three‐layer crust. This unique structure, which might represent a very old and large impact structure, could provide a rare window into Venus' ancient past. Key Points: We describe a unique ∼1,500 km‐diameter concentric ring complex and present detailed geologic maps of the structure and its host tesseraWe propose that this structure may represent a Valhalla‐type impact structure, as supported by geologic mapping and numerical modelingIf the hypothesis is valid, the complex is the largest impact structure recognized on Venus, with implications for early planet processes [ABSTRACT FROM AUTHOR]

Large topographic rises on Venus are regions thought to be formed in response to the presence of a mantle plume or mantle upwelling, equivalent to hot spots on Earth. In this work, we study the geology and evolution of one of these large topographic rises, Imdr Regio, based on geologic mapping and analysis of geophysical data of the area. Imdr Regio presents a complex structure with two very different areas: (a) an elevated southeast area that is dominated by volcanism associated with Idunn Mons, a large volcano that has been proposed as a site of recent or even active volcanism; (b) another elevated area in the northwest area that also has a large volcano (Arasy Mons), but that is dominated by volcanism and tectonic activity associated with the formation of the Olapa Chasma rift system. These two very differentiated topographically elevated areas also exhibit differences in their geology, volcanic and tectonic style, and geophysical characteristics, which leads us to suggest that more than the classic volcano‐dominated rise classification attributed to Imdr Regio the area could rather be considered as an intermediate or hybrid volcano‐rift dominated large topographic rise. The evaluation of the different genetic scenarios and its correspondence with the observed geology in the area suggests that the complex geology of Imdr Regio could be better explained if we consider models of hot spot evolution that involve the presence of several mantle plumes or secondary upwellings derived from a mantle plume emplaced at a deeper rheological boundary. Plain Language Summary: Large topographic rises on Venus are the equivalent to hot spots like those responsible for the formation of Hawaii on the Earth. We have studied the geologic evolution of one of these large topographic rises, Imdr Regio, and this research shows that Imdr Regio is complex with two differentiated areas. The southeast is dominated by a large volcano, Idunn Mons, that has been proposed as a site of recent or even active volcanism. In the northwest there is also a large volcano Arasy Mons, but the activity is dominated by the Olapa Chasma rift system. The presence of these two areas with differences in their geology, volcanic and tectonic style, and geophysical characteristics, leads us to suggest that, although this large topographic rise was classified as dominated by the volcano, it could indeed be better classified as an intermediate or hybrid volcano‐rift dominated rise. We also evaluate the different scenarios to explain its formation and conclude that the complex geology of Imdr Regio could be better explained if we consider models of hot spot evolution that involve the presence of several mantle plumes or secondary smaller plumes derived from a mantle plume emplaced at a greater depth. Key Points: We have studied the geology of Imdr Regio, a possible active hotspot on Venus, based on geologic mapping and analysis of geophysical dataImdr Regio presents complex geology dominated by Idunn Mons and Olapa Chasma, classifying it as a hybrid volcano‐rift large topographic riseThe complex geology and the topography of Imdr Regio suggest that it could be the result of multiple or secondary plumes in the area [ABSTRACT FROM AUTHOR]

We analyze data from multiple flybys by the Solar Orbiter, BepiColombo, and Parker Solar Probe (PSP) missions to study the interaction between Venus' plasma environment and the solar wind forming the induced magnetosphere. Through examination of magnetic field and plasma density signatures we characterize the spatial extent and dynamics of Venus' magnetotail, focusing mainly on boundary crossings. Notably, we observe significant differences in boundary crossing location and appearance between flybys, highlighting the dynamic nature of Venus' magnetotail. In particular, during Solar Orbiter's third flyby, extreme solar wind conditions led to significant variations in the magnetosheath plasma density and magnetic field properties, but the increased dynamic pressure did not compress the magnetotail. Instead, it is possible that the increased EUV flux at this time rather caused it to expand in size. Key findings also include the identification of several far downstream bow shock (BS), or bow wave, crossings to at least 60 RV ${\mathrm{R}}_{V}$ (1 RV ${\mathrm{R}}_{V}$ = 6,052 km is the radius of Venus), and the induced magnetospheric boundary to at least ∼ ${\sim} $ 20 RV ${\mathrm{R}}_{V}$. These crossings provide insight into the extent of the induced magnetosphere. Pre‐existing models from Venus Express were only constrained to within ∼ ${\sim} $ 5 RV ${\mathrm{R}}_{V}$ of the planet, and we provide modifications to better fit the far‐downstream crossings. The new model BS is now significantly closer to the central tail than previously suggested, by about 10 RV ${\mathrm{R}}_{V}$ at 60 RV ${\mathrm{R}}_{V}$ downstream. Plain Language Summary: We studied data from the missions Solar Orbiter, BepiColombo, and Parker Solar Probe to understand Venus' magnetotail. We focused on how Venus' magnetic environment interacts with the solar wind to create its magnetosphere. By looking at magnetic fields and plasma density, we figured out the size and movement of Venus' magnetotail, and found where its boundaries are. We noticed that these boundaries change a lot between missions, showing that Venus' magnetotail is very dynamic. Our main discoveries include finding boundary crossings like the bow shock 60 times Venus' radius downstream, and the magnetospheric boundary about 20 times Venus' radius downstream. This helps us understand how far the magnetosphere extends and improve our models of its shape. We also saw that the solar wind affects the magnetotail: during one mission, even though the solar wind was strong, it didn't squish the magnetotail; instead, it made it bigger because of increased solar radiation. Key Points: Venus' magnetotail is observed during nine spacecraft flybys revealing a dynamic structure reaching at least 60 RV downstreamAn improved bow shock model is presented for the deep tail regionThe pre‐existing model of the induced magnetospheric boundary is valid downstream to at least 20 RV [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 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]

There is a growing consensus that Venus is seismically active, although its level of seismicity could be very different from that of Earth due to the lack of plate tectonics. Here, we estimate upper and lower bounds on the expected annual seismicity of Venus by scaling the seismicity of the Earth. We consider different scaling factors for different tectonic settings and account for the lower seismogenic thickness of Venus. We find that 95–296 venusquakes equal to or bigger than moment magnitude (Mw) 4 per year are expected for an inactive Venus, where the global seismicity rate is assumed to be similar to that of continental intraplate seismicity on Earth. For the active Venus scenarios, we assume that the coronae, fold belts, and rifts of Venus are currently seismically active. This results in 1,161–3,609 venusquakes ≥Mw4 annually as a realistic lower bound and 5,715–17,773 venusquakes ≥Mw4 per year as a maximum upper bound for an active Venus. Plain Language Summary: Venus could be seismically active at the moment, but it is uncertain how many earthquakes (or to use the proper term: venusquakes) there could be in a year. Here, we calculate the minimum and maximum number of venusquakes we could expect in a given year on Venus based on different assumptions. If we assume there is not much seismic activity on Venus (comparable to the interior of tectonic plates on Earth), we find that we could expect about a few hundred venusquakes per year with a magnitude bigger than or equal to 4. For an estimate of the maximum amount of venusquakes, we assume that Venus has regions with more seismic activity: the so‐called coronae, fold belts, and rifts. Depending on our assumptions, we then find that more than 17,000 venusquakes with a magnitude bigger than or equal to 4 could occur in a year. Key Points: An inactive Venus with global background seismicity like Earth's continental intraplate seismicity has a few hundred quakes ≥Mw4 per yearA lower bound on an active Venus where fold belts, coronae, and rifts are seismically active predicts a few thousand quakes ≥Mw4 annuallyThe upper bound for an active Venus results in thousands (∼5,000–18,000) venusquakes ≥Mw4 per year [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]

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 explore the potential for repeat‐pass SAR Interferometry (InSAR) correlation to track volcanic activity on Venus' surface motivated by future SAR missions to Earth's sister planet. We use Hawai'i as a natural laboratory to test whether InSAR can detect lava flows assuming orbital and instrument parameters similar to that of a Venus mission. Hawai'i was chosen because lava flows are frequent, and well documented by the United States Geological Survey, and because Hawai'i is a SAR supersite, where space agencies have offered open radar data sets for analysis. These data sets have different wavelengths (L, C, and X bands), bandwidths, polarizations, look angles, and a variety of orbital baselines, giving opportunity to assess the suitability of parameters for detecting lava flows. We analyze data from ALOS‐2 (L‐band), Sentinel‐1 (C‐band), and COSMO‐SkyMed (X‐band) spanning 2018 and 2022. We perform SAR amplitude and InSAR correlation analysis over temporal baselines and perpendicular baselines similar to those of a Venus mission. Fresh lava flows create a sharp, noticeable decrease in InSAR correlation that persists indefinitely for images spanning the event. The same lava flows are not always visible in the corresponding amplitude images. Moreover, noticeable decorrelation persists in image pairs acquired months after the events due to post‐emplacement contraction of flows. Post‐emplacement effects are hypothesized to last longer on the Venusian surface, increasing the likelihood of detecting Venus lava flows using InSAR. We argue for further focus on repeat‐pass InSAR capabilities in upcoming Venus missions, to detect and quantify volcanic activity on Earth's hotter twin. Plain Language Summary: Scientists are still unsure whether volcanic activity is presently occurring on Venus. Future missions to Venus may have the opportunity to detect new lava flows on Venus' surface using a process called interferometry, in which two radar images of a planet's surface over time are compared to see what's changed between them. Interferometry has been used to detect lava and volcanic activity on Earth in the past. We use Hawai'i as a natural laboratory, measuring lava flows there with interferometry, under simulated conditions of a Venus mission, to test whether it will be possible for future Venus missions to track lava flows with interferometry. From the results of our case study, we believe that future missions to Venus such as NASA's VERITAS will be able to do exactly that. Key Points: Under favorable mission and instrument conditions, SAR Interferometry (InSAR) can detect lava flows on VenusInSAR correlation effects from thermal subsidence can be seen for several months post‐lava‐flow‐emplacementLava flows are more easily visible in InSAR correlation maps than in differenced SAR amplitude maps [ABSTRACT FROM AUTHOR]

Sapas Mons is a large shield volcano in Atla Regio on Venus. Its summit region is partially encircled by a system of pits and extensional faults (graben). The existence and configuration of this system have been attributed to stresses generated above the margin of a magma chamber spanning the region beneath the summit. The proposed stress‐generating mechanism includes either withdrawal of magma from or solidification of magma within such a chamber (Keddie & Head, 1994, https://doi.org/10.1007/bf00644896). To explore these hypotheses, we calculate Finite Element Method models of stresses and deformations resulting from magma chamber depressurization beneath a Sapas Mons‐sized edifice with axisymmetric geometry. For a range of magma chamber depths and vertical thicknesses, we determine the minimum under pressure that produces a stress state predicting failure in circumferential normal mode at the observed position of the graben system. We also determine maximum under pressure under two conditions: (1) no failure (thrust fault mode) predicted at the summit, and (2) predicted failure (thrust fault mode) limited to within 10 km of the summit. We find that successful models require sill‐like chamber geometry with vertical thicknesses <1.5 km (diameter to thickness aspect ratios >66:1), and chamber depth <8 km beneath the summit. Calculated reductions in chamber volume are comparable to volumes of late‐stage eruptive units mapped at Sapas Mons, favoring the magma withdrawal hypothesis for graben system formation. Evidence that unit 5 of Keddie and Head (1994, https://doi.org/10.1007/bf00644896) overlapped in time with, but largely postdated, the graben forming event renders it the most likely destination for magma removed from the chamber. Plain Language Summary: Sapas Mons is a large volcanic mountain on Venus, with lava flows that extend outwards for 100s of kilometers. Its distinctive summit region is partially encircled by a narrow ring of faults, which are most prominent on the east side. It has been proposed that a very wide but short chamber full of molten rock (magma) exists beneath the center of Sapas Mons, and that the faulting occurs when the top of the chamber moves downward, which can happen in two ways: (1) magma cools and solidifies within the chamber or (2) the magma leaves the chamber, presumably to erupt at the surface in lava flows. We calculated computer models of the process by which the magma chamber would contract in order to figure out the conditions under which the observed faults could happen (and also under which other types of faults, not seen, are avoided). The chambers must be less than 8 km below the summit and thinner than 1.5 km tall. We determined that the volume lost by the chamber is about the same as that estimated for a specific group of lava flows near the summit, a finding that favors scenario 2 above. Key Points: Sapas Mons volcano on Venus exhibits a partial ring of extensional faults that results from depressurization of an oblate magma chamberNumerical models of magma chamber deflation require extremely oblate chambers at shallow depths to explain observed fault patternsModeled chamber volume changes are comparable to volumes of the youngest mapped volcanic units, pointing to a magma withdrawal mechanism [ABSTRACT FROM AUTHOR]

On Venus, radar observations of the surface have highlighted two categories of craters: bright‐floored, interpreted as pristine, and dark‐floored, interpreted as being partially filled by lava. While volcanic resurfacing occurs within and outside craters in the plains, it seems mainly concentrated within the interior of dark‐floored craters in the crustal plateaus, suggesting that the magma is negatively buoyant there. Indeed, crater unloading may facilitate vertical ascent of a negatively buoyant magma by decompressing the underlying crust. However, the crater topography also generates a shear stress which would tend to horizontalize the vertical propagation of a dyke. We use numerical simulations of magma ascent in an axisymmetric crater stress field to demonstrate that, depending on the crust thickness and the magma‐crust density contrast, a negatively buoyant magma can indeed erupt only in the crater interior while remaining stored in the crust elsewhere. In particular, we identify four different behaviors depending on if and where a magma‐filled crack ascending below a crater reaches the surface. We draw a regime diagram as a function of two characteristic dimensionless numbers. For eruption to occur only in the crater interior requires a crust thinner than 45 km and a limited range of magma‐crust density contrasts, between 40 and 280 kg m−3 for crust thicknesses between 20 and 45 km, the permissible range decreasing for increasing crustal thicknesses. These results suggest that the crustal plateaus may not be particularly thick and could be slightly differentiated, but probably not very felsic. Plain Language Summary: The Magellan mission revealed two categories of impact craters at the surface of Venus: the pristine bright‐floored and the dark‐floored craters, which are interpreted as craters partially filled by smooth lava after their formation. In the crustal plateaus of Venus, the magma reaches the surface mainly within craters, suggesting that it is denser than the crust. Because of the crater negative topography, the underlying crust is decompressed relative to its surroundings, which, in turn, facilitates magma ascent below the crater despite its negative buoyancy. We first gather surface observations on a set of craters located in the crustal plateaus of Venus to construct a characteristic fresh crater topography. We then use a model of magma ascent below a crater in the crust of Venus to constrain the magma and crust densities as well as the initial magma storage depth that allow for magma eruption within the crater interior only. We show that magma reaches the surface only in the interior of the crater if the crust is slightly less dense than the magma and if it is not too thick (≤45 km in thickness). Key Points: We identify four different behaviors for magma‐filled crack propagation below cratersWe draw a behavior diagram as a function of two dimensionless numbers characterizing dyke propagation below a craterMagma infilling of dark‐floored craters in Venus' plateaus requires a crustal thickness ≤45 km and a small crust‐magma density contrast [ABSTRACT FROM AUTHOR]

Venus boasts an abundance of volcanoes and volcano‐like structures. Synthetic aperture radar images of the surface have revealed extensive evidence of volcanism, including lava flows and edifices. Volcanic activity is further supported by crater statistics, and analysis of topography and gravity data. Unique to Venus, coronae are quasi‐circular volcano‐tectonic features exhibiting diverse volcanic characteristics. Despite this, volcanism is often under‐represented in formation models. We identify a new subset of coronae that display topographic changes subsequent to the emplacement of lava flows within their fracture annuli, pointing to the critical role of volcanic and magmatic processes in the formation of these coronae. Through spherical‐harmonic distribution analysis, we find that this new subset is spatially related to the full coronae database, pointing to an intrinsic process of coronae formation. Furthermore, coronae exhibit strong correlations and similar spectral shapes at low spherical harmonic degrees with large volcanoes, suggesting a shared geodynamic origin. Our findings underscore the pivotal role of volcanism in coronae formation and highlight the need for future research to integrate magmatic and volcanic processes more comprehensively into geophysical models. Such models would better capture the complex interactions between volcanic emplacement, magmatic activity, and lithospheric dynamics on Venus. Plain Language Summary: Venus's surface has a large number of volcanoes and features with characteristics similar to volcanoes. Radar imagery of the surface reveals signs of volcanism such as lava flows and volcanically built mountains. A unique volcanic feature, found only on Venus, are coronae, which have circular fractures and various types of associated volcanic activity. Explanations of how coronae form often do not consider the role of volcanic activity. In our study, we identify a new group of coronae that have undergone changes in topography after lava erupted and flowed over them, which has been interpreted as volcanism having a central role in corona formation. The locations of this subset of coronae on the surface fit well with all other coronae, suggesting that the processes that caused this topographic change occur throughout the corona population and are a basic part of how all coronae form. Additionally, we find that coronae have a similar pattern on the surface to large volcanoes, which indicates a shared volcanically based origin. Our work shows that in order to better understand coronae, we need to consider the role of volcanism in their formation. Key Points: A new subset of coronae shows topographic changes post‐lava flow emplacementSpectral analysis reveals strong long‐wavelength similarities between coronae and large volcanoesVolcanism plays a crucial role in corona formation and should be considered central in future models of formation [ABSTRACT FROM AUTHOR]

Since December 2015, Ultraviolet Imager (UVI) onboard Akatsuki has been observing Venus clouds at the wavelengths of 283 and 365 nm. Horizontal winds near the cloud top derived from the UVI images over ∼7 earth years are analyzed to elucidate spatial and temporal variability of the superrotation and planetary‐scale waves. Zonal winds averaged over the analysis period are asymmetric with respect to the equator, being faster in the southern hemisphere. This asymmetry varied temporarily and was occasionally reverted. Comparison of the winds from the two wavelengths suggests that it is uncertain whether the asymmetry is in the wind distribution or in the sensing altitude for winds. Mean zonal winds representing the superrotation exhibited broad low‐frequency variability with spectra resembling the red noise spectra. This is indicative of the presence of internal variability rather than responses to periodical external forcing. Planetary‐scale waves with zonal‐wavenumber 1 at periods around 4 and 5 days, which have been interpreted as equatorial Kelvin and Rossby waves, respectively, are quantified. While the ∼5‐day waves have nearly constant frequencies, the ∼4‐day waves have variable phase speeds that follow the superrotation speed. This result indicates that the ∼5‐day waves are likely to extend over a large depth below the cloud top and that the ∼4‐day waves are likely to be confined near the cloud top. Their possible generation mechanism through the coupling of Kelvin and Rossby waves is discussed. This study further reports wind variability of 10 to 15‐day periodicity, thermal‐tide structure, and comparison with minor species observations. Plain Language Summary: Akatsuki is the only currently operational artificial satellite of Venus. It has been conducting imaging observations at two ultraviolet wavelengths since December 2015. By measuring the movement of cloud features in the images, we obtain horizontal winds near the cloud‐top altitude where the famous superrotation is maximized. By using wind data over ∼7 earth years, we show that the superrotation speed varies over time, showing a broad spectrum. This is indicative of internally created variability rather than periodic variability created by external forcing. We also reveal that mean westward winds that characterize the superrotation have some differences between the northern and southern hemispheres and that these differences vary over time. However, the data do not allow us to conclude whether the asymmetry is in the winds or in the sensing altitude. Venus has long been known for having two kinds of planetary‐scale waves with periods around 4 and 5 days, but their vertical distributions are unknown. We indicate that the 5‐day waves have a deeper vertical distribution than the 4‐day waves from the differences in the long‐term changes in their frequencies. We further characterize the thermal tides excited by solar heating and suggest wind variability at periods of 10–15 days. Key Points: Venus' superrotation as measured near the cloud top exhibits rich low frequency variations indicating internal variabilityPlanetary‐scale ∼4‐ and ∼5‐day waves are suggested to reside in different altitude rangesTemporally varying hemispheric asymmetry is found in zonal winds, which might partly be due to the sensing altitude asymmetry [ABSTRACT FROM AUTHOR]

Mars and Venus have atmospheres but lack intrinsic dipole magnetic fields. Consequently, the solar wind interaction at each planet results in the formation of an induced magnetosphere. Our work aims to compare the low‐altitude (< 250 km) component of the induced magnetic field at Venus and Mars using observations from Pioneer Venus Orbiter and Mars Atmosphere and Volatile EvolutioN. We restrict the in‐situ data from Mars to regions of weak crustal magnetism. At Venus, it has long been known the vertical structure of the induced magnetic field profiles have recurring features that enable them to be classified as either magnetized or unmagnetized. We find the induced field profiles at Mars are more varied, lack recurring features, and are unable to be classified in the same way. The solar zenith angle dependence of the low‐altitude field strength at both planets is controlled by the shape of the magnetic pileup boundary. Also, because the ionospheric thermal pressure at Venus is often comparable to the solar wind dynamic pressure, the induced fields are weaker than required to balance the solar wind by themselves. By contrast, induced fields at Mars are stronger than required to achieve pressure balance. Lastly, we find the induced fields in the magnetized ionosphere of Venus have a weaker dependence on solar wind dynamic pressure than the induced fields at Mars. Our results point to planetary properties, such as planet‐Sun distance, having a major effect on the properties of induced fields at nonmagentized planets. Key Points: Unlike Venus, the induced magnetic field profiles at Mars are unable to be categorized into magnetized and unmagnetized statesAt both planets, the solar zenith angle dependence of the induced field strength is controlled by the shape of the magnetic pileup boundaryInduced fields at Mars are stronger than expected if assuming the fields form to achieve pressure balance with the oncoming solar wind [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]

Gravitational instabilities can develop at volcanoes of any size and in any geological setting and can lead to various types of volcano deformation, ranging from small‐scale landslides on the flanks of the edifice to large, deep‐seated sector collapses. As volcanoes grow, they impose an increasing load on the underlying basement, which can result in styles of gravitational deformation where the edifice sags or spreads outward under its own weight. In this study, we utilize our previously developed global catalog of volcanoes on Venus to analyze a subset of edifices that appears to have undergone gravitational deformation. We identify 162 volcanoes that display morphological evidence for gravitational deformation and classify them into four main categories based on associated deformational structures: landsliding, sector collapse, spreading, and sagging. Landsliding of volcano flanks or full sector collapse are the most common and geographically widespread deformational styles on Venus, and account for ∼64% of our data set. Edifices exhibiting structures linked to volcano spreading and sagging are relatively rare; nonetheless, we note for the first time on Venus the presence on a shield volcano of flank terraces, structures linked to sagging. We find that deformed volcanoes are distributed globally, are found at a range of elevations, are spatially proximal to a variety of tectonic structures, and are associated with various crustal thickness values, which together suggest that there are numerous drivers of volcano deformation on Venus. Plain Language Summary: The effect of gravity works to destabilize volcanoes of all shapes and sizes and in all geological settings on Earth. In fact, gravity can lead to failure of small or even large parts of a volcano. As volcanoes grow and become heavier, they either weigh down the ground below them or, if the ground is very rigid, flatten outwards. Here, we used a catalog of volcanoes on Venus that we previously published to identify and describe all the examples of gravity‐deformed volcanoes on the planet. We found more than 160 such volcanoes and divided them into four major classes based on different types of collapse features. Deformed volcanoes are located across the entire surface of Venus, with a slightly higher concentration found in the Beta–Atla–Themis region. Furthermore, these collapsed edifices are situated in areas with different tectonic structures and are located at varying elevations across the planet, suggesting that there are multiple reasons why a volcano on Venus might collapse. Key Points: We identify 162 volcanoes displaying structures associated with gravitational deformation on VenusDeformed volcanoes are geographically widespread but are somewhat concentrated in the Beta–Atla–Themis regionWe note examples of flank terraces on Tepev Montes, a structural indicator of volcano sagging that has not yet been documented on 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]

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]

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]

Coronae are quasi‐circular volcano‐tectonic features on Venus. Four critical observations have been identified within the coronae population, including fracture annuli, a wide range of diameters, complex and varied topography, and various types of associated volcanic features. Geophysical models have attempted to replicate their formation from a variety of lithospheric processes but struggle to recreate all four of the critical observations. Volcanism is an often overlooked characteristic in corona formation models. Paleotopographic techniques are applied to lava flows associated with Atete Corona and Aruru Corona in the Beta‐Atla‐Themis region to investigate post‐emplacement changes in topography. Our results indicate marked divergence between lava flow orientation and the modern slope within the fracture annuli of the coronae. Intra‐annular flows at Atete Corona were emplaced on a surface that was reoriented by up to ∼180°. Intra‐annular flows at Aruru Corona were emplaced on a surface that was reoriented between 90° and 145°. Lava flows on the flanks of both coronae diverge less than those within the fractures. This finding suggests a progression of volcanism that starts at the interior of the corona and migrates outward to the fracture annuli. The role of volcanism, both intrusive and extrusive, is likely to play a more substantial role in the corona formation. Incorporating melt migration into geophysical models could significantly enhance our comprehension of the processes underlying the formation of coronae. Plain Language Summary: Coronae are circular structures found only on the surface of Venus with characteristics of both volcanoes and tectonically formed features. There are four key observations have been identified about these structures: they are surrounded by a circle of fractures, they come in a wide range of sizes, they vary in the shape of their topography, and they are often associated with volcanic activity. Current models that attempt to explain their formation through processes within Venus' outer shell (or lithosphere) have difficulty accounting for all these observations. In this study, lava flows related to two coronae, Atete Corona and Aruru Corona, are examined using techniques that provide information on how the surface changes over time. Our results show that there is a significant mismatch between the direction of the lava flows and the slopes they are on top of. In some places, the lava flows appeared to have "flowed" uphill. Additionally, the differences between flows near the coronae centers and the modern slopes are greater than those at the edges of the coronae, indicating that volcanic activity started from the coronae interiors and moved outward. These findings suggest a crucial role for both surface and subsurface volcanism in the coronae formation. Key Points: Geophysical models of corona formation struggle to recreate critical observations and underestimate the role of volcanismLava flows associated with Atete and Aruru Corona are not aligned with modern downslope directions and show migrating volcanic centersThe role of volcanism is likely to play a more substantial role in corona formation and may help explain their diverse morphologies [ABSTRACT FROM AUTHOR]

Venus is the only other Earth‐sized planet in the Solar System but it does not exhibit evidence of plate tectonics that dominates geological processes on Earth. Surface deformation on Venus is mainly driven by mantle convection and plume‐lithosphere interactions, likely represented by the widespread development of the circular volcano‐tectonic features known as coronae. Here, we present a joint study of mission data analysis and 3D modeling of asymmetric coronae on Venus. We systematically analyze 155 of the largest coronae on Venus in terms of surface topography and morphology. We establish that 75% of those coronae are radially asymmetric, and further sub‐categorize them based on their adjacent topography. This analysis reveals that many asymmetric coronae are positioned at a topographic transition between a lowland and plateau (termed topographic margin). With state‐of‐the‐art 3D numerical models, we investigate the physical processes behind plume‐margin interactions on Venus. We find that several tectonic styles may be responsible for asymmetric coronae at topographic margins, including lowland‐sided subduction, plateau‐sided lithospheric dripping, and an embedded plume. The gradient in lithospheric strength across the topographic margin controls these tectonic styles, and larger gradients enhance lithospheric resurfacing and the lifetime of the coronae. We also find that the density increase associated with the basalt‐to‐eclogite phase change provides the extra negative gravitational force required for downgoing crust to be recycled into the mantle. The models presented in this study reproduce a wide set of asymmetrical corona features found on Venus and suggest that they are generally more long‐lived than symmetric coronae. Plain Language Summary: Venus surface tectonics and volcanism are very dissimilar to modern Earth and in particular show development of many hundreds of circular and oval‐shaped "corona" structures, ranging in size from 60 to nearly 2,000 km. Here, the 155 largest coronae on Venus are systematically analyzed in terms of surface morphology and topographic positioning. We establish that the vast majority of large coronae on Venus have asymmetric features and are positioned at a topographic margin. We present the first‐ever plume‐margin numerical models in 3D which show several tectonic styles of plume‐margin interactions on Venus. The styles depend on the lithospheric structure and the density change of crustal material at depth. Importantly, the models indicate that asymmetric coronae at topographic margins are longer lived structures that symmetric coronae. Key Points: A new topographic classification of large coronae on Venus reveals that most coronae are radially asymmetric and bound a topographic marginWe present 3D tectono‐magmatic models of plume‐margin interactions on Venus which reveal several geodynamic evolution scenariosLateral lithospheric changes and the basalt‐to‐eclogite phase change mostly control the tectonic styles and coronae activity lifetime [ABSTRACT FROM AUTHOR]

The occurrence of Venusian lighting has been debated for decades. Terrestrial lightning generates whistler waves, and many whistlers have been observed in Venus's ionosphere and induced magnetosphere. Venusian lightning occurrence rates derived from these whistler observations are relatively high. However, optical flashes on Venus are exceedingly rare and Venus encounters by multiple spacecrafts have not detected lightning. These non‐detections and rare optical observations are consistent with low Venusian lightning occurrence rates, which is incompatible with the high whistler‐derived rates. We present observations of whistlers during a Parker Solar Probe Venus gravity assist and eliminate lightning as a possible source. These waves are observed at an altitude of 0.39 Venus radii on Venus' nightside with planetward propagation and are simultaneous with Langmuir waves. This provides a mechanism for whistler generation near Venus that does not require lightning, and suggests that whistler‐based lightning occurrence rates may be overestimated. Plain Language Summary: Whistler waves are a type of plasma wave. These waves can be generated in several ways, including by lightning. Every lightning strike on Earth generates a whistler wave, but only some of the whistler waves in near‐Earth space are generated by lightning. Many whistler waves have been detected near Venus and have been used to argue that lightning likely occurs on Venus at a relatively high rate. However, other signatures of lightning (including flashes of light in the sky) on Venus are very rare, which indicates that Venusian lightning must occur at a very low rate. The discrepancy between these different signatures of lightning on Venus means that we do not know how often Venus actually experiences lightning. We use data from Parker Solar Probe during a Venus gravity assist to study whistler waves that occurred on the nightside of Venus, very close to the planet. We observe that these waves are traveling toward Venus, which means they could not have been generated by lightning. This shows that whistler waves can occur near Venus without being generated by lightning and indicates that the occurrence rates of Venusian lightning based on whistler wave observations might be overestimated. Key Points: Whistler waves were observed at an altitude of 0.39 Venus radii on Venus's nightside with planetward Poynting vectorLangmuir waves occurred simultaneously with the whistlers, suggesting electron beam driving with magnetotail originsLightning is eliminated as a possible generation mechanism for these whistler waves [ABSTRACT FROM AUTHOR]

Images of Venusian clouds taken at ultraviolet (UV) wavelengths frequently exhibit mesoscale cellular structures at low latitudes. To obtain clues regarding the origin of these structures, we studied the temporal variation of the mesoscale UV contrast using 283‐ and 365‐nm images taken by the ultraviolet imager (UVI) onboard the Akatsuki spacecraft. The 283‐nm channel is mostly affected by SO2 at the cloud top and the 365‐nm channel is mostly affected by an unknown absorber, though both absorbers are thought to influence both wavelengths. We defined the mesoscale as a spatial scale roughly below 1,000 km, where the effect of large‐scale streaky patterns is not significant according to the spatial spectra of 283‐nm images taken by UVI and 2.02‐μm images taken by the near‐infrared camera (IR2) onboard Akatsuki. We found that the temporal variation of the standard deviation of the mesoscale UV contrast is dominated by quasi‐periodic oscillations with amplitudes of 30%–50% relative to the mean value and periods of around 4–5 Earth days. Oscillations of the planetary‐scale UV contrast with similar periods were also observed, suggesting that the mesoscale structures are influenced by planetary‐scale waves. The mesoscale contrast tends to be enhanced when the background albedo decreases in the course of the propagation of planetary‐scale waves. This correlation suggests that the solar heating near the cloud top level feeds the mesoscale dynamics. An enhancement of the mesoscale contrast in the afternoon was seen at a wavelength of 365 nm. Plain Language Summary: On Venus, the brightness pattern of the cloud top shows signs of convection, where heat is transported either upward or horizontally through the fluid motion. These processes could have a large impact on material and energy transportation on the planet. We examined ultraviolet (UV) cloud images captured by the Akatsuki Venus orbiter to track changes in contrast over time at both a planetary and mesoscale (below 1,000 km). Unlike visible wavelengths, Venus' clouds display changes in brightness over time and space when viewed at UV wavelengths. The UV contrast at the mesoscale was found to oscillate with periods of around 4–5 Earth days. Similar periods of oscillation are observed in the planetary‐scale brightness variation, suggesting that planetary‐scale waves influence the motion at a scale below 1,000 km. The contrast at this scale tends to be enhanced when the background becomes darker. This relation implies that the heating of clouds by the Sun enhances vertical or horizontal inhomogeneity of the temperature and then powers the observed convection. Key Points: The temporal variation of the mesoscale ultraviolet (UV) contrast of Venusian clouds was studied using images taken by the UV camera on AkatsukiThe mesoscale contrast was found to oscillate with periods of 4–5 Earth days, which are also the periods of planetary‐scale wavesThe mesoscale contrast tends to be enhanced when the background becomes darker, suggesting that solar heating feeds the mesoscale dynamics [ABSTRACT FROM AUTHOR]

Shocklets and short large‐amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady‐state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach‐number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%. Plain Language Summary: We discover that Venus, like Earth, also has magnetic structures called Shocklets and short large‐amplitude magnetic structures (SLAMS) in its foreshock region, which is the area upstream of the planet where the interplanetary magnetic field is connected to its bow shock. Shocklets and SLAMS are common in the foreshock of Earth. However, Shocklets have not been observed at Venus before, and SLAMS have only been seen once, and then only during a large disturbance of the space near Venus. Thus it is unknown if SLAMS and Shocklets can form in the foreshock of a planet as close to its star as Venus. We used observations from the European Space Agency's Venus Express orbiter (2006–2014) to identify these structures in the Venusian foreshock. The structures were found to be present during periods of high solar wind activity, and a lower limit on how often they occur is at least 14% of the time. These findings provide new insights into the space environment around Venus and may help us understand the differences in the space environments of different planets. Key Points: Shocklets and short large‐amplitude magnetic structures (SLAMS) can form in the steady‐state foreshock of Venus despite the magnetosphere being 1/10th the size of EarthsThe Venusian Shocklets and SLAMS had comparable magnetic signatures to those reported near Earth, but may be rarerAnalysis of the solar wind at 0.72AU suggests Shocklets and SLAMS occur during high Alfvén mach‐numbers with a lower limit on occurrence rate of ≳14% [ABSTRACT FROM AUTHOR]

Every planet or moon with an ionosphere is thought to generate a weak electrical potential which helps ions overcome gravity and escape to space. A pilot study at Venus by Collinson et al. (2016, https://doi.org/10.1002/2016GL068327) indicated a planetary potential an order of magnitude stronger than expected. Here we present a statistical study of the electrical potential drop in the ionosphere of Venus, which was found to be an average of 7.04 ± 2.19 V. However, these strong potentials measured by Venus Express are likely atypical and extreme outliers associated with a transient phenomenon in the Venusian ionosphere. We posit they are associated with transient and sporadic density cavities in the ionosphere and may be the result of sporadic electrostatic double layer formation in the dayside ionosphere. Plain Language Summary: Previous investigations have suggested that Venus has a much stronger electrical potential in its ionosphere than expected. This electrical potential is important as it helps charged particles escape into space. At Venus, the potential can be strong enough to directly propel all water‐group ions (including oxygen) to escape velocity. Thus, understanding what is responsible for such a strong potential at a planet so similar to Earth is of utmost importance for understanding what makes terrestrial planets habitable. We present a statistical study of all measurements by the European Space Agency's Venus Express Orbiter (2006–2014). This statistical study revealed an average potential of 7.04 ± 2.19 V, far exceeding that at Mars and Earth. However, this measurement was only possible during 30 out of 3,189 orbits of Venus Express. The measurements could only be made at solar minimum and the reasons for this are yet unknown. More research is needed to investigate what generates this strong electric field. To accomplish this, future missions to Venus are necessary with a more comprehensive instrument suite that can measure the planet's electrical potential more consistently. Key Points: We present a statistical survey of all Venus Express measurements of the electrical potential drop in the Venusian ionosphereMean potential was 7.04 ± 2.2 V, but such strong potentials are likely due to transient and local phenomena possibly electrostatic double layersFuture missions to Venus are necessary to consistently measure its intrinsic electrical field and investigate its typical strengths [ABSTRACT FROM AUTHOR]

Lightning in the atmosphere of Venus is either ubiquitous, rare, or non‐existent, depending on how one interprets diverse observations. Quantifying when and where, or even if lightning occurs, would provide novel information about Venus' atmospheric dynamics and chemistry. Lightning is also a potential risk to future missions, which could float in the cloud layers (∼50–70 km above the surface) for up to an Earth‐year. Over decades, spacecraft and ground‐based telescopes have searched for lightning at Venus using many instruments, including magnetometers, radios, and optical cameras. Two optical surveys (from the Akatsuki orbiter and the 61‐inch telescope on Mt. Bigelow, Arizona) observed several flashes at 777 nm (the unresolved triplet emission lines of excited atomic oxygen) that have been attributed to lightning. This conclusion is based, in part, on the statistical unlikelihood of so many meteors producing such energetic flashes, based in turn on the presumption that a low fraction (<1%) of a meteor's optical energy is emitted at 777 nm. We use observations of terrestrial meteors and analogue experiments to show that a much higher conversion factor (∼5%–10%) should be expected. Therefore, we calculate that smaller, more numerous meteoroids could have caused the observed flashes. Lightning is likely too rare to pose a hazard to missions that pass through or dwell in the clouds of Venus. Likewise, small meteoroids burn up at altitudes of ∼100 km, roughly twice as high above the surface as the clouds, and also would not pose a hazard. Plain Language Summary: Artists depicting the atmosphere of Venus love to include lightning bolts to emphasize its hellish environment. Even though missions like DAVINCI would most likely be safe from strikes as they descend quickly through the atmosphere, long‐lived aerial platform missions supported by large balloons floating in the cloud layer ∼50–70 km above the surface might not be so fortunate. Do engineers need to build aerial platforms with the toughness (and thus expense) required to survive a lightning strike? Quantitative estimates of lightning strike frequency are inconsistent based on different forms of evidence. Observations of certain electromagnetic signals, interpreted as lightning in the clouds, suggest a strike rate several times that of Earth's lightning. In comparison, optical flash rates at Venus, as observed at the Mt. Bigelow observatory in Arizona and by the Akatsuki mission currently orbiting Venus, suggest a far lower flash rate. In this study, we argue that these optical flashes were plausibly produced by meteor fireballs ∼100 km above the surface, not by lightning in the clouds. If so, then lightning poses no significant threat to balloon missions in the clouds of Venus. Lightning may still exist at the surface, produced by Aeolian processes or explosive volcanism. Key Points: We investigate whether meteor fireballs could have produced the optical flashes that have been detected at Venus and attributed to lightningWe find that flashes from meteor fireballs are statistically likely to occur at the observed rates and brightnessThere is no affirmative evidence that lightning is a hazard to missions that pass through or dwell within the clouds of Venus [ABSTRACT FROM AUTHOR]

The long‐wavelength gravity and topography of Venus are dominated by mantle convective flows, and are hence sensitive to the planet's viscosity structure and mantle density anomalies. By modeling the dynamic gravity and topography signatures and by making use of a Bayesian inference approach, we investigate the viscosity structure of the Venusian mantle by constraining radial viscosity variations. We performed inversions under a wide range of model assumptions that consistently predicted the existence of a thin low‐viscosity zone in the uppermost mantle. The zone is about 235 km thick and has a viscosity reduction of 5–15 times with respect to the underlying mantle. Drawing a parallel with the Earth, the reduced viscosity could be a result of partial melting as suggested for the origin of the asthenosphere. These results support the interpretation that Venus is a geologically active world predominantly governed by ongoing magmatic processes. Plain Language Summary: On Venus, convective up and downwellings in the mantle are intrinsically linked to density variations in the interior. The manner in which the planet is deformed by these mantle flows depends upon its viscosity, and this in turn affects the gravity and topography signals that were recorded by orbiting spacecraft. We tested a large range of model parameters that describe the mantle viscosity on Venus and retrieved the viscosity structure that is compatible with the observations. Our results indicate the presence of a low viscosity zone beneath the Venusian lithosphere in the uppermost mantle. In this region, the viscosity is one order of magnitude smaller than that of the underlying mantle. Starting at a depth of about 80 km and extending over about 235 km, this low viscosity zone could reflect the presence of partial melting and, similarly to the Earth, an asthenosphere on Venus. The presence of partial melt in the interior of Venus supports recent observations of a volcanically active planet and holds major implications for present‐day magmatic activity. Key Points: The long‐wavelength gravity and topography of Venus are investigated in the spectral domain using a dynamic loading modelBayesian inference constraints on the mantle viscosity structure indicate the existence of a low viscosity zone in the upper mantleThe low viscosity zone is potentially associated with partial melting beneath the lithosphere [ABSTRACT FROM AUTHOR]

We present a model for the thermal evolution of Magma Ocean (MO) in interaction with a degassing atmosphere of H2O and CO2. The interior model is based on parameterized convection and is coupled to the atmospheric Model of Marcq et al. (2017, https://doi.org/10.1002/2016JE005224) through heat and volatiles. A new equation for the mass balance of volatiles is implemented, correcting Salvador et al. (2017, https://doi.org/10.1002/2017je005286). We found that the domain for water condensation is extended: for instance, depending on the cloud cover and resulting albedo, 0.13 Earth's ocean mass might be sufficient to form a water ocean on early Venus (instead of 0.3 MEO in Salvador et al. (2017, https://doi.org/10.1002/2017je005286)). Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle melting curves (which depend on mantle composition), the treatment of the atmosphere (e.g., gray or convective‐radiative) and the treatment of the last stages of the MO solidification (e.g., episodic resurfacing, stagnant lid...). We also apply our results to exoplanets. They suggest that liquid water might be present at the surface of Trappist‐1e and 1f, provided that those planets' volatile primitive contents were dominated by H2O and CO2. Plain Language Summary: We present a numerical model of a cooling magma ocean (MO) and the atmosphere degassing from it. The solidification of the MO leads to the enrichment of the silicate melt in volatiles, thus favoring degassing. Both reservoirs interact via heat and volatile exchange, where the volatiles are H2O and CO2. The aim of this model is to explore the influence of the atmosphere on the surface conditions after the MO stage, and especially the conditions required for the condensation of a water ocean to occur. For example, for an early Earth at 1 AU initially containing 1 Earth's water ocean mass, a water ocean could form for initial CO2 content as large as 1,000 bars. Moreover, a tenth of the actual Earth's water ocean mass would be sufficient to generate a water ocean on early Venus. Liquid water could also be present on the surface of the two exoplanets Trappist‐1e and 1f. Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle composition, the treatment of the heat transfer in the atmosphere, and the treatment of the last stages of the MO solidification. Key Points: An initial CO2 content up to 1,000 bars would not prevent condensation of a water ocean on the early Earth0.13 Earth's ocean mass would be sufficient to form a water ocean on early VenusLiquid water may be present on the surface of Trappist‐1e and 1f [ABSTRACT FROM AUTHOR]

Active volcanism was (and potentially still is) an important process that shapes the Venus surface and its detection is a primary goal for the planned VERITAS and EnVision missions. Therefore, understanding lava flow emplacement and timing on Venus is important. We adapt the terrestrial PyFLOWGO thermorheological model to Venus conditions to assess the effects on channelized lava flow propagation. We first initiate the model with terrestrial basaltic parameters and progressively adapt it to Venusian conditions in five steps: (a) gravity, (b) ambient atmospheric temperature, (c) specific heat capacity and wind speed, (d) atmospheric density, and (e) coupled convective and radiative heat flux. Compared to Earth, the slightly lower gravity on Venus resulted in a lower flow velocity, a higher crust coverage, and a very minor increase in flow length (0.1%). Increasing the ambient atmospheric temperature reduced heat loss and produced a (77%) longer flow; whereas next accounting for the atmospheric specific heat capacity and wind speed increased the flow length slightly more (81%). However, increasing the atmospheric density resulted in a shorter lava flow (13%) due to more efficient cooling. Finally, accounting for coupled convective and radiative heat loss due to the strong CO2 infrared absorption resulted in an increase of the flow length (∼75%). Although the model applies only to channelized, cooling‐limited flows, these results reveal that for the same effective effusion rate and topography, a Venusian lava flow travels a longer distance than the equivalent flow on Earth and its cooling should be detectable by future orbital instruments. Plain Language Summary: Lava flow length and velocity is partially controlled by the environmental conditions of a planet (e.g., gravity, atmospheric temperature, and density). Observations reveal that Venus volcanism is an important process that shaped its surface. However, the extreme surface environment influences the emplacement of these lava flows differently than on Earth. In this study, we quantify the impact of the Venusian planetary and environmental conditions on lava flow advance using the PyFLOWGO model. Although this model is one‐dimensional and applies only to channelized, cooling‐limited flows, it is exceedingly adaptable, and by far is the most cited model in the literature. Here, we adapt an Earth lava flow to Venus conditions in five steps: (a) gravity, (b) atmospheric temperature, (c) atmospheric specific heat capacity and wind speed, (d) atmospheric density, and (e) coupling atmospheric convective and radiative heat flux. Compared to Earth conditions, the lava flow is most affected by the heat flux difference caused by the CO2‐rich Venusian atmosphere, which results in a 75% longer flow than the same flow on Earth due to the decrease in heat loss to the atmosphere. Results for a 100 km Venusian lava flow indicate that it would be observable by the upcoming missions. Key Points: We model the thermorheological properties of lava during flow emplacement under Venus conditionsFor this model, coupling atmospheric convective and radiative heat loss has a significant impact on the modeled Venus flowUsing equivalent starting parameters, a basaltic channelized lava flow would travel ∼75% further on Venus than on Earth [ABSTRACT FROM AUTHOR]

One of Venus' most enigmatic landforms is Baltis Vallis, the longest channel on the surface (∼7,000 km long). We identify a possible mid‐channel island that implies a south to north flow direction during formation. However, since the flow direction of Baltis Vallis is otherwise not well constrained, we analyze topographic conformity in both flow directions. In either case, topography appears to be altered across most analyzed wavelengths after the formation of Baltis Vallis. Fourier analysis shows two ranges of prominent wavelengths, 225 ± 15 km and ∼3,500 ± 1,200 km. The shorter wavelengths correspond to deformation belts that cross Venus' low plains. The longest is plausibly associated with the dynamic uplift wavelength of the crust by mantle plumes, but is less robustly detected. Higher resolution observations provided by the VERITAS and EnVision missions can help resolve the source location of Baltis Vallis and constrain if the longest wavelength postdated the canale's formation. Plain Language Summary: Venus' surface is covered in a plethora of strange landforms, at least from the perspective of Earth. One of the longest is an about 7,000 km channel named Baltis Vallis, comparable to the Amazon and Nile rivers, but instead likely formed by volcanic processes. Baltis Vallis serves as a unique opportunity on Venus due to its length. The channel recorded surface altering processes in its topography, but we first check if the channel retained topographic information from when it initially formed. Our test shows that the topography has been altered by later processes and those processes should dominate the signal in analysis of the current topography. That analysis shows 2 length‐scales are overrepresented in the topography. The shorter length‐scale correspond to thin mountain range‐like features that cross Venus' low plains. The longest wavelength is plausibly associated with uplift of the crust by mantle plumes and this value will be useful when creating models of Venus' interior. Key Points: A possible mid‐channel island in the longest channel on Venus implies a south to north flow directionWe show that the topography and morphology of this channel was modified along most of its lengthFourier analysis of the channel's topography shows a group of prominent wavelengths at ∼210–240 km, that we link to deformation belts [ABSTRACT FROM AUTHOR]

A new Venus‐ESD‐Chamber (VEC) and peripheral systems were designed and built to simulate Venus lightning. It consists of three subsystems (a) electrostatic discharge (ESD) generation, (b) environmental pressure, temperature, gas composition control & monitoring, and (c) optical and non‐optical sensors. We conducted arc discharge experiments in air, in CO2, and in Venus major gas mixture (CO2‐N2, 96.5% ± 1.5%:3.5% ± 1.5%) under 10, 350, 700, and 1,000 mbar pressures, that correspond to the 50–75 km altitude range in the cloud layer of Venus. Plasma and Raman spectra, plus gas sensors, and GC‐MS were used to identify the ESD products and to semi‐quantify CO and O3 generated by ESD. We have found all species of free radicals that have been found in previous simulation studies using different discharge technologies, including some important species in CO2‐N2 system, nitrogen oxides and CN. In addition, we found three species (O3, N2+, and C2) that have not been previously reported. Our results suggest that electron flux and kinetic energy are the determining factors for the type of generated free radical species and gas pressure plays a less important role. We found that the quantity of CO changes with the type of ESD. The detection of O3 in this study suggests that lightning might be one of the sources of O3 observed in the Venusian atmosphere. OI emission line at 777.4 nm is the most prominent line in our plasma spectra of FD, consistent with the intense optical flash observed by the Lightning and Airglow Camera (LAC) on the Akatsuki mission. Plain Language Summary: Lightning is a common phenomenon on Earth and plays an important role in atmospheric chemistry as well as in atmosphere‐surface interaction. The thick atmosphere and strong convective activities in Venus cloud layers could ignite lightning. Evidence of lightning on Venus (optical and electric types) has been reported since the 1970s, including the observation made by the most recent mission Akatsuki in 2020. Here, we report the detection of 15 types of free radicals generated during a set of arc‐type electric discharges in simulated Venus atmosphere with two major Venus gases (CO2 & N2) and in a pressure range corresponding to the Venus cloud layer (50–75 km altitude range). These free radicals are ions and neutral atoms/molecules in excited states, which have extremely high chemical reactivity and high kinetic energy. They could play crucial roles in Venus atmospheric chemistry and might be helpful to interpret some past mission observations for example, nitrogen oxides and O3. Key Points: Building a Venus‐ESD chamber enables simulation of Venus lightning and radical sensingArc discharge was realized to simulate lightning in the cloud layer of Venus15 types of free radicals and excited atoms/molecules were characterized using four sensors [ABSTRACT FROM AUTHOR]

The thermal structure of the upper atmosphere in the Venus polar region is reproduced by the assimilation of horizontal winds in low‐ and mid‐latitudes derived from the Akatsuki ultra‐violet images. The obtained structure is well consistent with infrared and radio occultation measurements. In particular, the unique thermal features in the Venus polar vortex such as the cold collar and the warm polar region in our model are realistic: the level where the cold collar is located and the temperature difference between the cold collar and the warm polar region are consistent with data. The reasons why the thermal structure of the upper atmosphere in the Venus polar region is realistic are that the zonal wind distribution around the cloud top level and the structure of the residual mean meridional circulation induced by the thermal tides are improved with respect to the model without data assimilation. Our results also suggest that the thermal structure in the Venus upper polar region is closely related to the atmospheric dynamics. Plain Language Summary: Data assimilation is one of the powerful techniques to correct an output from a numerical model by comparing with the observations and enables us to obtain the modeling results consistent with the measurements. In this study, by the data assimilation of horizontal winds in low‐ and mid‐latitudes derived by the Akatsuki ultra‐violet images, the thermal structure of the upper atmosphere in the Venus polar region has been reproduced by the General Circulation Model. The zonal wind distribution around the cloud top level in the model is well consistent with the measurements due to the data assimilation, and then the unique thermal structure in the Venus polar vortex such as the cold collar and the warm polar region reproduced by the model is also improved with respect to the model without data assimilation because the structures of the atmospheric circulation and the atmospheric waves are realistic due to the improvement of the zonal wind distribution. Our results also suggest that the thermal structure of the upper atmosphere in the Venus polar region is closely related to the atmospheric dynamics. Key Points: The thermal structure in the Venus upper polar region is reproduced by the assimilation of horizontal winds derived from Akatsuki UVIThe reproduced thermal structure becomes realistic and consistent with the observations due to the data assimilationOur results suggest that the thermal structure in the Venus upper polar region is closely related to the atmospheric dynamics [ABSTRACT FROM AUTHOR]

Venus is home to many thousands of volcanic landforms that range in size from much less than 5 km to well over 100 km in diameter. Volcanism is clearly a major, widespread process on Venus, and is a principal expression of the planet's secular loss of interior heat. Without sufficient in situ data to clearly determine its internal structure, we can use the morphological and spatial properties of volcanoes across the planet to help place constraints on our understanding of the volcanic characteristics and history of Venus. With the Magellan synthetic‐aperture radar full‐resolution radar map left‐ and right‐look global mosaics at 75 m‐per‐pixel resolution, we developed a global catalog of volcanoes on Venus that contains ∼85,000 edifices, ∼99% of which are <5 km in diameter. We find that Venus hosts far more volcanoes than previously mapped, and that although they are distributed across virtually the entire planet, size–frequency distribution analysis reveals a relative lack of edifices in the 20–100 km diameter range, which could be related to magma availability and eruption rate. Through spatial density analysis of volcanoes alongside assessments of geophysical data sets and proximal tectonic and volcanic structures, we report on the morphological and spatial patterns of volcanism on Venus to help gain new insights into the planet's geological evolution. Plain Language Summary: There are many thousands of volcanoes on the surface of Venus. These volcanoes provide clues into the interior properties of the planet, properties that are otherwise largely inaccessible to us at present. We used the Magellan synthetic aperture radar imagery to catalog volcanoes across Venus at a global scale. Our resulting database contains ∼85,000 volcanoes, ∼99% of which are less than 5 km in diameter. Although there are volcanoes across almost the entire surface of the planet, there seem to be relatively fewer volcanoes in the 20–100 km diameter range, which may be a function of magma availability and eruption rate. Patterns in spatial clustering of volcanoes in conjunction with geophysical data sets and proximal tectonic and volcanic structures can reveal the nature and distribution of volcanic landforms on Venus. Key Points: We present a new global catalog of volcanoes on Venus that includes ∼85,000 edifices, ∼99% of which are <5 km in diameterWe developed an automated approach to delineating volcanic fields—high spatial concentrations of small volcanoes—from our catalogThere is a lack of edifices in the 20–100 km dimeter range on Venus [ABSTRACT FROM AUTHOR]

Venus is a terrestrial planet with dimensions similar to the Earth, but a vastly different geodynamic evolution, with recent studies debating the occurrence and extent of tectonic‐like processes happening on the planet. The precious direct data that we have for Venus is very little, and there are only few numerical modeling studies concerning lithospheric‐scale processes. However, the use of numerical models has proven crucial for our understanding of large‐scale geodynamic processes of the Earth. Therefore, here we adapt 2D thermomechanical numerical models of rifting on Earth to Venus to study how the observed rifting structures on the Venusian surface could have been formed. More specifically, we aim to investigate how rifting evolves under the Venusian surface conditions and the proposed lithospheric structure. Our results show that a strong crustal rheology such as diabase is needed to localize strain and to develop a rift under the high surface temperature and pressure of Venus. The evolution of the rift formation is predominantly controlled by the crustal thickness, with a 25 km‐thick diabase crust required to produce mantle upwelling and melting. The surface topography produced by our models fits well with the topography profiles of the Ganis and Devana Chasmata for different crustal thicknesses. We therefore speculate that the difference in these rift features on Venus could be due to different crustal thicknesses. Based on the estimated heat flux of Venus, our models indicate that a crust with a global average lower than 35 km is the most likely crustal thickness on Venus. Plain Language Summary: Venus is a planet that is roughly the same size as the Earth, and recent studies have debated the style of Venusian tectonics and how it differs from Earth. One such tectonic process is known as "rifting," where a tectonic plate gets extended and forms structures as in East Africa on Earth. These rift structures have been observed on Venus as well, but it is unclear how they formed under Venus' high surface temperature and pressure. Computer simulations have improved our understanding of the rifting process on Earth, so here we apply them to Venus to discover how rifting processes work under Venusian conditions. Our results show that the crust needs to consist of strong rocks in order for rifting to take place under Venus' conditions. The thickness of the crust also has a direct effect on the evolution of the rift and a thin crust favors the production of magma on Venus. We compare the surface topography of the rifts in our simulations with rift topographies observed on Venus. We find that different crustal thicknesses fit different rift observations on Venus. Therefore, we speculate that differences in rifts on Venus could be related to differences in the crustal thickness. Key Points: A strong crustal diabase rheology is required to localize strain and develop rifts in our modelsA thin crust produces the melt required to support the hypothesis of Venus being currently volcanically activeCrustal thicknesses of 25 and 35 km result in surface topographies comparable with rift topography observations of Venus [ABSTRACT FROM AUTHOR]

We report two experiments using 13 mineral and rock samples exposed to a complex synthetic Venus atmosphere composed of nine gases for durations of 30 and 11 days conducted using the NASA Glenn Extreme Environments Rig (GEER). Examination of our run products using a scanning electron microscope equipped with an energy dispersive spectrometer reveals secondary minerals predominantly formed from reactions of Fe and Ca in the solid samples with sulfur in the atmospheric gas, results largely predicted in the literature, and indicating that such reactions between rocks and the atmosphere at the Venus surface may occur rapidly. Samples that displayed larger degrees of reaction include calcite (forming Ca‐sulfate), Fe‐Ti oxide (forming an Fe,S phase), biotite (forming an Fe,S phase), chalcopyrite (forming a new Cu,Fe‐sulfide and a Ag,Cl phase), and Mid‐Ocean Ridge Basalt glass (forming a Ca‐ and S‐bearing phase, Fe‐ and S‐bearing phase, and an Fe‐oxide); pyrite was observed to be stable in our 30‐day experiment. These reactions indicate that the fS2 of the experiments was above or at the high end of what is thermodynamically predicted for the Venus surface. Apatite, feldspars, actinolite, and quartz did not change in this time frame. The presence of multiple S species in the GEER atmosphere may explain the dissimilarities to the style of reactions seen in previous experiments with simpler gas mixtures. Plain Language Summary: The surface conditions of Venus are unique in our solar system, where rocks are exposed to a sulfur‐rich atmosphere at 460°C and pressures ∼90× that of the surface of the Earth. The Glenn Extreme Environments Rig (GEER), located at NASA Glenn Research Center, is the world's first laboratory vessel to mimic Venus surface conditions (including 9 atmospheric gases) over durations of weeks to months. We placed 13 rock and mineral samples in GEER for 11 and 30 days to observe changes in the samples due to reactions with the simulated Venus atmosphere. We find that Fe‐ and Ca‐bearing minerals react with S and Cl in the gas, to produce discrete secondary minerals. We find that sulfur gas is the dominant driver of mineral reactions in this experiment and that the mixture of gases in GEER may account for some of the differences in the reaction products seen here as compared to previous experiments. Some mineral surface compositions change significantly, suggesting that these changes will be rapid on Venus. The style and rate of these reactions will help us better understand the climate history recorded in Venus surface rocks from remote sensing measurements from spacecraft at the end of this decade. Key Points: Mineral weathering experiments were conducted for up to 30 days under Venus surface conditions, including a nine‐gas atmospheric mixtureCalcite, biotite, basaltic glass, chalcopyrite, and Fe‐Ti oxide all reacted to produce secondary minerals dominated by Ca, Fe, and SOur results indicate the fS2 of the experiments was above or at the high end of what is thermodynamically predicted for the Venus surface [ABSTRACT FROM AUTHOR]

Venusian cloud structure and variation are strongly linked to atmospheric dynamics. Past near‐infrared measurements have found cloud variation such as zonal‐wavenumber‐1 cloud marking and cloud discontinuity. However, their formation mechanism is still not well understood. To investigate the Venusian cloud structure and its variation, we have developed a Venus GCM incorporating cloud condensation, evaporation, sedimentation, and simple atmospheric chemistry to represent the H2SO4 cycle. The GCM takes into account cloud particles with radii of 0.3, 1.0, 1.26, and 3.13 μm (Modes 1, 2, 2', and 3, respectively) based on past in situ observations. The simulated latitudinal trends of the cloud top and bottom structures are qualitatively consistent with past observations. Zonally averaged cloud mass loading was the largest and smallest in low and middle latitudes, respectively, and maintained by a mechanism similar to that of past 2‐D numerical studies. At the equator, the column integrated optical depth at 1 μm varied between 33 and 50, which is in good agreement with past observations. This variation consists of two types of cloud mass loading changes between 46 and 52 km. One is a rapid small‐scale variation induced by gravity waves. The other is a quasi‐periodic zonal‐wavenumber‐1 variation coupled with an equatorial Kelvin wave, which is similar to the observed cloud marking. Our results showed that the vertical wind associated with the Kelvin wave is essential for maintaining the quasi‐periodic variation, along with the condensation/evaporation by the temperature variation. The vertical‐wind‐induced cloud generation also suggests a relationship to the cloud discontinuity. Plain Language Summary: Venus is completely shrouded in thick sulfuric acid (H2SO4) clouds. The Venusian cloud structure is determined by atmospheric circulation, chemistry, and cloud microphysics, and its morphology is thought to manifest atmospheric activities such as waves and instabilities. Near‐infrared observations have discovered quasi‐periodic features in low latitudes, such as planetary‐scale cloud marking and discontinuity. However, the formation mechanism of the quasi‐periodic features is not well understood because of the complicated cloud process. In this study, we have developed a three‐dimensional global numerical model which simulates cloud condensation/evaporation and transport processes coupled with simple chemistry representing the H2SO4 cycle in the Venusian atmosphere. The simulated latitudinal trends of the cloud top and bottom structures are qualitatively consistent with past observations. In low latitudes, a planetary‐scale cloud marking propagates quasi‐periodically, consistent with previous near‐infrared observations. Our results suggest that vertical wind associated with a planetary‐scale wave is essential for maintaining the cloud marking. This cloud formation mechanism is possibly related to the cloud discontinuity suggested by recent observations. Key Points: Cloud opacity variation in low latitudes is investigated by a Venus general circulation model with simple cloud parameterizationThe simulated opacity variation is consistent with past observations, composed of variations induced by gravity and Kelvin wavesVertical wind associated with the Kelvin wave is essential for maintaining the quasi‐periodic cloud variation [ABSTRACT FROM AUTHOR]

Until recently, the lower to middle cloud region of Venus had been supposed to be dynamically quiet, accommodating nearly steady superrotating westward flow. However, observations of the regions by Akatsuki, the latest Venus orbiter operating since 2015, have revealed a variety of cloud features indicative of vortices and waves. Here we report another, and arguably the most conspicuous, example. Akatsuki's near‐infrared imager IR2 captured gigantic vortices rotating cyclonically on 25 August 2016. By using winds estimated by cloud tracking, the feature is shown to be quantitatively consistent with barotropic instability. The size of the vortices (∼1,000 km) and their spacing (∼2,500 km) are more than several times greater than the vortex‐like features reported previously from the observations of Venus, and they are also greater than the largest barotropic instability observed in the Earth's troposphere. Plain Language Summary: Hydrodynamical instabilities play important roles in the general circulation of the Earth and planetary atmospheres. Barotropic instability is a kind of instability that arises from horizontal differences in predominantly parallel horizontal flows. We report herewith the first concrete evidence of its occurrence in the atmosphere of Venus. Before this study, reports are limited to vortex‐like cloud features whose appearance is consistent with this instability, but no analyses of flows have been conducted before. The cloud feature like a vortex street reported in this study has a spatial scale far greater than any of previously reported ones, and our study shows that it is dynamically consistent with barotropic instability. Key Points: An event of barotropic instability, whose scale is greater than 1,000 km, was found by the Akatsuki Venus orbiterThe discovery reinforces the recent view that the lower to middle cloud regions are dynamically active, promoting further studies [ABSTRACT FROM AUTHOR]

Barometers floating on high‐altitude balloons in the relatively clement cloud layer on Venus could detect and characterize acoustic waves generated by seismic activity, avoiding the need for high‐temperature electronics required for surface seismology. Garcia et al. (2022, https://doi.org/10.1029/2022GL098844) recently demonstrated the detection of low‐frequency sound (infrasound) caused by earthquakes of magnitudes 7.3 and 7.5 from stratospheric balloons nearly 3,000 km away from the epicenter. They provided a preliminary demonstration of earthquake magnitude and location inversion, and the determination of S‐ and Rayleigh wave velocities using only their acoustic signature. Large earthquakes produce low‐frequency seismic waves that penetrate the interiors of planets; their detection at continental‐scale distances from a high‐vantage point demonstrates the feasibility of balloon‐based investigations of Venus' interior. We contextualize these results within the effort to perform seismology on Venus from balloons, discuss its limitations, and share perspectives on open research questions in this area. Plain Language Summary: Scientists have peered inside Earth, the Moon, and Mars by recording how seismic waves pass through them. Venus' interior is a mystery, though, because the heat and pressure at its surface have thus far prevented direct measurement of seismic activity. Balloons with pressure recorders higher up in the Venusian atmosphere, where it is much cooler, can listen for the sounds the seismic waves make as a proxy for directly measuring ground motion. Before sending the balloons to Venus, it is important to make sure that this idea would actually work. The fact that (Garcia et al., 2022, https://doi.org/10.1029/2022GL098844) were able to record sound from large earthquakes thousands of kilometers away on Earth means that one should be able to do the same thing on Venus as well. While there are still details to work out, listening for quakes on Venus from balloons just got a major boost here on Earth. Key Points: A network of stratospheric balloons captured infrasound from several large earthquakesThis is the first detection of seismic activity from airborne sensors at continental distancesA similar network on Venus could capture and geolocate seismic activity [ABSTRACT FROM AUTHOR]

In their 2022 study, Byrne and Krishnamoorthy (https://doi.org/10.1029/2021je007040) extrapolated to Venus the most comprehensive record of eruptions on Earth, to estimate the frequency of volcanic events on the second planet. The approach underlying this extrapolation is necessarily based on assumptions for which there is little supporting evidence; moreover, the eruptive record on Earth is far from complete because, for example, submarine events are considerably undercounted. Byrne and Krishnamoorthy (2022, https://doi.org/10.1029/2021je007040) discussed at length the limitations of their study, cautioning that their estimates on the frequency of volcanic eruptions on Venus are simply that—estimates, albeit amenable to testing by future missions to the planet. The comment by van Zelst on the Byrne and Krishnamoorthy (2022, https://doi.org/10.1029/2021je007040) study identified a calculation error in one specific scenario considered in that earlier study. The other points raised in the van Zelst comment are either consistent with the range of uncertainties discussed in, or focus on topics that have no bearing on, the Byrne and Krishnamoorthy (2022, https://doi.org/10.1029/2021je007040) study. The scientific conclusions of the Byrne and Krishnamoorthy study remain unchanged. Plain Language Summary: Although there are strong hints of active volcanism on Venus, how often volcanoes erupt there is wholly unknown. In their 2022 study, Byrne and Krishnamoorthy made a first attempt to estimate how common volcanic eruptions are on Venus by taking the best record of eruptions on Earth and applying it to Venus. van Zelst (2022b, https://doi.org/10.1029/2022JE007448) wrote a comment in response to the study by Byrne and Krishnamoorthy, pointing out that those authors made a mistake in their calculation for one of the possibilities they considered. The comment by van Zelst made several other points, but none changes the overall conclusions of the study by Byrne and Krishnamoorthy. The bottom line is that the only way to be really see how often volcanoes erupt on Venus is to send spacecraft there. Key Points: The comment by van Zelst on Byrne and Krishnamoorthy (2022, https://doi.org/10.1029/2021je007040) identifies a single calculation errorThe overall conclusions of that 2022 study either remain unchanged by or are unrelated entirely to the van Zelst comment [ABSTRACT FROM AUTHOR]

Byrne and Krishnamoorthy (2022), https://doi.org/10.1029/2021je007040 estimated the frequency of volcanic eruptions on Venus by scaling the eruption frequency obtained from a database containing Earth data. In reproducing their study, I found that the estimated number of new and ongoing volcanic eruptions on Venus in a given year is approximately 42, instead of the previously reported 120 eruptions. This updated estimate of Byrne and Krishnamoorthy (2022) based on the assumption that data from Earth can be scaled to Venus is an important step toward quantifying volcanism on Venus. However, it is important to note that in this estimate, the amount of volcanism associated with rifting is underestimated and subduction‐related volcanism is overestimated. The annual volcanic flux on Venus resultant from the estimated amount of volcanic eruptions aligns with previous estimates of Venus' volcanic flux based on, for example, chemical reaction times and geological mapping. Applying the same method of estimating volcanic eruption frequency to the other terrestrial planets in the Solar System indicates that the Earth scaling method is perhaps not universally applicable, especially concerning bodies with vastly different tectonic regimes. Plain Language Summary: Much is still unknown about Venus, including how many volcanic eruptions might occur on its surface. This information is important as it would help with designing space missions and could greatly improve the understanding of the interior and dynamics of the planet. Byrne and Krishnamoorthy (2022), https://doi.org/10.1029/2021je007040 used statistical methods and a database containing information about volcanic eruptions on Earth to provide the first estimates of the amount of volcanic eruptions in a given year on Venus. They reported an estimated 120 volcanic eruptions on Venus per Earth year. I have reproduced their study and found that they made an error in their statistical method. Instead, the estimated amount of volcanic eruptions on Venus in an Earth year is approximately 42. This estimate contains uncertainties due to the lack of knowledge of volcanic eruptions in the oceans on Earth and the possibility of subduction occurring on Venus. However, despite these uncertainties, the updated estimate of Byrne and Krishnamoorthy (2022) is an important step toward exploring Venus as a volcanic world. Key Points: Assuming that data from Earth can be scaled to Venus directly, I estimate that ∼42 eruptions could take place on Venus annuallyRift volcanism is significantly underestimated in the database, so the estimated volcanic eruption frequency on Venus is conservativeThe volcanic flux associated with the estimated volcanic eruption frequency aligns with previous estimates [ABSTRACT FROM AUTHOR]

The recently selected NASA VERITAS and DAVINCI missions, the ESA EnVision, the Roscosmos Venera‐D will open a new era in the exploration of Venus. One of the key targets of the future orbiting and in situ investigations of Venus is the identification of volcanically active areas on the planet. The study of the areas characterized by recent or ongoing volcano‐tectonic activity can inform us on how volcanism and tectonism are currently evolving on Venus. Following this key target, Brossier et al. (2022, https://doi.org/10.1029/2022GL099765) extend the successful approach and methodology used by previous works to Ganis Chasma in Atla Regio. Here we comment on the main results published in Brossier et al. (2022, https://doi.org/10.1029/2022GL099765) and discuss the important implications of their work for the future orbiting and in situ investigation of Venus. Their results add further lines of evidence indicating possibly recent volcanism on Venus. Key Points: The manuscript by Brossier et al. (2022, https://doi.org/10.1029/2022GL099765) extends the successful approach and methodology used by previous workWe comment here on the main results by Brossier et al. (2022, https://doi.org/10.1029/2022GL099765) and discuss the important implications for the future investigations of VenusTheir results add further lines of evidence indicating possibly recent volcanism on Venus [ABSTRACT FROM AUTHOR]

The presence of phosphine (PH3) in the atmosphere of Venus was reported by Greaves et al. (2021, https://doi.org/10.1038/s41550-020-1174-4), based on observations of the J = 1–0 transition at 267 GHz using ground‐based, millimeter‐wave spectroscopy. This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of atmospheric phosphorous‐bearing gases. Here we present results from a search for PH3 on Venus using the German REceiver for Astronomy at Terahertz Frequencies instrument aboard the Stratospheric Observatory for Infrared Astronomy aircraft, over three flights conducted in November 2021. Multiple PH3 transitions were targeted at frequencies centered on 533 and 1,067 GHz, but no evidence for atmospheric PH3 was detected. Through radiative transfer modeling, we derived a disk‐averaged upper limit on the PH3 abundance of 0.8 ppb in the altitude range 75–110 km, which is more stringent than previous ground‐based studies. Plain Language Summary: We performed observations using a unique, flying telescope—the Stratospheric Observatory for Infrared Astronomy—to search for a gas called phosphine (PH3) in the atmosphere of Venus, which has been suggested to be an indicator for life. Our observations showed no evidence of PH3, in contrast to the original claim, and we provide a stringent upper limit on its abundance. Two other recent studies using different telescopes also found no evidence for PH3 on Venus, in agreement with our present result. Key Points: A recent detection of phosphine (PH3) (a possible biomarker) on Venus at millimeter wavelengths has been called into question by subsequent workWe performed far‐infrared spectroscopic observations of Venus using the German REceiver for Astronomy at Terahertz Frequencies instrument onboard the Stratospheric Observatory for Infrared Astronomy aircraftPH3 was not detected, and a strict upper limit on its atmospheric abundance of 0.8 ppb was derived between 75 and 110 km [ABSTRACT FROM AUTHOR]

Magellan synthetic aperture radar observations of Venus revealed a small number of deposits in the highland regions that were suggested to have formed from pyroclastic density currents. Studying these deposits is useful for understanding the nature of pyroclastic activity and eruptive history on Venus. The proposed pyroclastic deposits occupy the uppermost unit in local stratigraphy and are found near exceptionally high reflectivity (R $R$∼0.6) units in the highlands. Their radar properties include high copolarized backscatter (∼−8 to −15 dB) and moderate emissivity values (∼0.70–0.88) in the 12.6 cm wavelength Magellan data acquired at incidence angles between ∼15° and 45°. We aim to characterize the structure of these deposits by modeling the observed backscatter and emissivity as a function of different physical and dielectric properties and shallow subsurface stratigraphy. Three different physical scenarios focusing on three different scattering mechanisms—surface scattering, subsurface scattering from buried dielectric horizons, and volume scattering from buried, distributed scatterers—are considered. By comparing the model results to Magellan observations, we narrow down likely pyroclastic deposit structures. We show that the deposits are likely analogous to dense, welded ignimbrites with high surface roughness. We also investigate other possible but less likely scenarios of a thin, low‐density, low‐loss mantling pyroclastic deposit on top of high reflectivity units and a thick, low‐density, low‐loss deposit with ∼5–10 volume % of scatterers of sub‐wavelength size. Future multiwavelength, multipolarization radar observations from VERITAS and EnVision may enable unambiguous characterization of these deposits. Plain Language Summary: A handful of deposits with bright, featureless appearance have been identified on the slopes of large volcanic structures on Venus. These deposits are thought to be dominated by fragmented rocks that formed from water‐rich magma. Investigating these deposits is therefore helpful for understanding magmatic and interior water on Venus. In this paper, we use radar data sets from the Magellan mission and theoretical modeling techniques to characterize the physical properties of these deposits and make inferences about their emplacement conditions. Our results indicate that the Venusian deposits have high bulk density in comparison to similar rock fragment‐rich volcanic deposits on Earth. We interpret this high density to be a result of fusing together of individual rock fragments under high temperatures and suggest that it is possible to maintain high emplacement temperatures for an extended period of time on Venus's surface. Our results have implications for fragmented magma cooling rates on Venus. Radar imagery and topography from upcoming missions to Venus will help in further understanding the formation of volcanic deposits under Venus's ambient conditions. Key Points: Magellan radar observations of proposed pyroclastic deposits are inconsistent with surface scattering from incoherent clastic unitsScattering models show three likely scenarios: (a) Welded deposit, (b) pyroclastic mantling of high‐reflectivity unit, and (c) lithic‐strewn depositMultiwavelength, multipolarization data from upcoming missions will help in further characterizing the proposed pyroclastic deposits [ABSTRACT FROM AUTHOR]

Super‐rotation and waves are sensitive to horizontal subgrid‐scale fourth‐order diffusion in long‐term time integrations of a dynamical core under a Venus‐like condition. The rigid‐body rotation component of the super‐rotation intensifies as the diffusion strengthens, and the fluid dynamic similarity of the nondimensional winds is found among the different diffusions. In the experiments with weak diffusion, the super‐rotation is weak in the presence of strong poleward eddy heat flux, enhancing the downward angular momentum transport by the Eliassen–Palm (E–P) flux. In contrast, the strong super‐rotation is developed, and both the poleward eddy heat and vertical E–P fluxes are weak in the strong horizontal diffusion experiments. Because the waves with high zonal wave numbers and poleward heat fluxes are strongly dissipated, the vertical E–P fluxes become weak and the contribution of subgrid‐scale vertical diffusion becomes large in the momentum budget. As the horizontal diffusion strengthens, the phase velocities of the equatorial waves increase due to the faster background zonal flow (i.e., mean zonal flow). Although strong empirical diffusion produces strong super‐rotation, it is still unknown whether it is valid. Thus, we must carefully assess the robustness of the super‐rotation in the long‐term simulation based on the sensitivity test of horizontal diffusion. Plain Language Summary: Large differences were observed among the general circulation models under the same Venus‐like idealized condition. We focused on horizontal subgrid‐scale diffusion as one of the factors for the differences. The atmospheric super‐rotation (which rotates at a faster rate than the planetary rotation) intensifies as the diffusion strengthens, and the fluid dynamic similarity is found among the different diffusions. In the experiments with weak diffusion, the super‐rotation is weak in the presence of the strong poleward eddy heat flux, enhancing the downward angular momentum transport. In contrast, the strong super‐rotation is developed, and both the poleward eddy heat and vertical E–P fluxes are weak in the strong horizontal diffusion experiments. Because waves with high zonal wave numbers and poleward heat fluxes are strongly dissipated, the vertical E–P fluxes become weak, and the contribution of subgrid‐scale vertical diffusion becomes large in the momentum budget. Our sensitive study clarified that the tuning up of the empirical diffusion parameter is important in Venus general circulation modeling and contributes to the assessment of the robustness of the simulated super‐rotation of Venus. Key Points: Vertical momentum flux by zonal‐mean meridional circulation exceeds that by eddies for strong horizontal subgrid‐scale diffusionStronger horizontal subgrid‐scale diffusion leads to faster super‐rotation and waves in long‐term Venus‐like simulationsNondimensional wind profiles are dynamically similar among experiments with different diffusions [ABSTRACT FROM AUTHOR]

Exploration of Venus in the 1970–1990s revealed that the geology of Venus, the most Earth‐like of the terrestrial planets, was decidedly un‐Earth‐like, with no plate tectonics, and no record of the first 80% of its history. A major outstanding question is whether Venus is still volcanically active today. We find that regions of Ganis Chasma have low radar emissivity values, due to low volumes of high dielectric minerals formed by surface‐atmosphere weathering on the timescales of around 10 s Ma. This confirms the presence of geologically recent volcanism in association with this major tectonic rift zone. The spatial correspondence of this emissivity signature with transient thermal anomalies suggests that Venus has been volcanically active at this site for at least the last few decades, a prediction that can be tested with space missions to Venus in the coming decade. Key Points: Radar anomalies in Ganis Chasma correspond to transient bright spots seen in infrared dataLow radar emissivity values suggest recent volcanic and tectonic activity on VenusLava flows in Ganis Chasma may have erupted over the last 30 years [ABSTRACT FROM AUTHOR]

The ground movements induced by seismic waves create acoustic waves propagating upward in the atmosphere, thus providing a practical solution to perform remote sensing of planetary interiors. However, a terrestrial demonstration of a seismic network based on balloon‐carried pressure sensors has not been provided. Here we present the first detection of seismic infrasound from a large magnitude quake on a balloon network. We demonstrate that quake's properties and planet's internal structure can be probed from balloon‐borne pressure records alone because these are generated by the ground movements at the planet surface below the balloon. Various seismic waves are identified, thus allowing us to infer the quake magnitude and location, as well as planetary internal structure. The mechanical resonances of balloon system are also observed. This study demonstrates the interest of planetary geophysical mission concepts based on seismic remote sensing with balloon platforms, and their interest to complement terrestrial seismic networks. Plain Language Summary: After a quake, the surface of our planet vibrates like the surface of a drum. These vibrations generate sound waves at low frequencies that propagate upward in the atmosphere. These signals from two earthquakes have been recorded by barometers on board a network of long duration high altitude balloons deployed by the Strateole‐2 experiment. The analysis of these records demonstrates that the amplitude and arrival time of the vibrations are properly predicted by our modeling tools. The oscillations of the balloon/gondola system forced by the acoustic waves are also observed, but the quake distance and magnitude can be estimated only from the data recorded on board the balloon gondolas. Moreover, the shape of the pressure perturbations recorded by the balloons contains the seismic surface waves that are sounding the first hundred kilometers of the Earth's internal structure. These observations clearly demonstrate the interest of a similar experiment in the atmosphere of Venus to sound its poorly known internal structure. Key Points: An earthquake is detected by a network of barometers on board balloons in the stratosphere for the first timeQuake magnitude and distance are estimated from the infrasound created by seismic body waves and surface wavesBalloons can act as mobile seismometer network in the atmosphere of Earth and Venus [ABSTRACT FROM AUTHOR]