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

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

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

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]

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]

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]

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]

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]

Characteristic features of the Venus ionosphere below the V1 base, named as V0 layer, have been studied using the Radio Science payload onboard Akatsuki orbiter. An ionospheric layer below the V1 base is known to be present in the Venus ionosphere but found to be geographically localized, seen mostly during the daytime between 55 and 90° solar zenith angle (SZA). We, for the first time, show its presence at different latitudes and SZA, including near the equator during the local noon and post‐sunset hours. The maximum density of this layer was ∼4 × 1010 m−3 at the altitude range of 110 ± 4 km. In the absence of in‐situ measurements, it's difficult to comment on the origin but the presence of such layers during post‐sunset hours suggests their meteoric origin as the observed altitudes are consistent with the height range predicted by the meteor models. Other possible sources of such layers are also discussed. Plain Language Summary: Akatsuki orbiter has been conducting radio occultation (RO) measurements since 2016 to study the atmosphere and ionosphere of Venus using an onboard Radio Science experiment. A total of 34 electron density profiles have been obtained so far, among which 25 are from the dayside. There are six profiles that show an enhancement in the electron density below 120 km altitude, the base of V1 layer. We report the presence of such layers near the equatorial region, both during the day and night time. We have named it the V0 layer because they are no longer geographically localized phenomena, earlier believed to be. A most probable explanation for the presence of this layer is the ionization of metallic molecules associated with meteor showers. As photo‐ionization is a main source of ions in the Venus ionosphere, its presence during the post‐sunset hours supports the idea of their meteoric origin as the night side of Venus receives no solar radiation. However, to confirm V0 as a sporadic or consistent layer, we need to investigate with in situ measurements supported by more frequent RO experiments. Key Points: First observations of V0 layer in the Venus ionosphere near the subsolar point at solar zenith angle (SZA) ∼5°, and well past the solar terminator at SZA ∼108°First observation of V0 layer at the equator during the local noonAkatsuki radio science measurements, for the first time, show that such layers are not SZA dependant [ABSTRACT FROM AUTHOR]

Natural and anthropogenic events may create low frequency sound waves, or infrasound, that can travel for vast distances in planetary atmospheres. They permit the remote monitoring of geophysical activity over local to global scales. Most studies have utilized ground‐based recorders, but it is possible to deploy acoustic sensors to altitudes of over 50 km. Such elevated platforms can capture sounds that their surface analogs cannot access. High altitude balloons and low altitude aerostats are filling this observation gap, but key environments remain out of reach of both of these. Recent work by den Ouden, Smets et al. (2021) addressed this with a new instrumentation platform—a large seabird flying just above the ocean's surface. Their work demonstrates that, infrasound sensing using heavier‐than‐air platforms in windy environments is possible, which has implications both terrestrially (e.g., extending sensor networks over the oceans) and extraterrestrially (proposed or planned missions to Venus and Titan). Plain Language Summary: Many things make sound on Earth and other planets. If these sounds are deep enough, they can travel a long way. Scientists typically record these sounds using instruments that sit on the ground, despite the fact that there is an ocean of air lying above them. Only in the last few years have we begun to explore the sounds in this vast region, and typically we use tethered or free floating balloons to do so. There's some places we can't reach though, like just above the surface of the ocean. den Ouden, Smets et al. (2021) solved this problem by putting sound recorders on wandering albatrosses. The birds flew far and wide across the ocean, recording both nearby and distant sound along the way. This is a big deal, because no one knew it was possible to pick up faint sounds amid the rushing wind caused by the birds' flight. It shows that, we can likely put sound recorders on aircraft such as drones (both low and close to the ground, and high in the sky), getting useful results in the process. Listening in on the atmospheres of Venus and Saturn's moon Titan just became a lot more promising as well. Key Points: A variety of geophysical phenomena generate low frequency acoustic waves, or "infrasound"A seabird‐mounted sensor captured infrasound just above the open oceanInfrasound can be recorded on flying platforms even in windy environments [ABSTRACT FROM AUTHOR]

Extreme temperature and pressure conditions on the surface of Venus present formidable technological challenges against performing ground‐based seismology. Efficient coupling between the Venusian atmosphere and the solid planet theoretically allows the study of seismically generated acoustic waves using balloons in the upper atmosphere, where conditions are far more clement. However, earthquake detection from a balloon has never been demonstrated. We present the first detection of an earthquake from a balloon‐borne microbarometer near Ridgecrest, CA in July 2019 and include a detailed analysis of the dependence of seismic infrasound, as measured from a balloon on earthquake source parameters, topography, and crustal and atmospheric structure. Our comprehensive analysis of seismo‐acoustic phenomenology demonstrates that seismic activity is detectable from a high‐altitude platform on Earth, and that Rayleigh wave‐induced infrasound can be used to constrain subsurface velocities, paving the way for the detection and characterization of such signals on Venus. Plain Language Summary: The interior structure of Venus remains unknown due to lack of in situ seismic observations. Adverse temperature and pressure conditions on the Venusian surface limit the lifetimes of landers to a few hours, which poses a technological challenge against performing ground‐based seismology to detect venusquakes. Seismic energy on Venus, as on Earth, can be transmitted into the atmosphere through mechanical coupling and propagate as low‐frequency sound (infrasound). Infrasound from earthquakes travels long distances and has been detected from ground‐based stations. This mechanism may allow the detection of seismically generated pressure disturbances on Venus using balloons, enabling remote seismology from its upper atmosphere, where temperature and pressure conditions are far more clement and longer mission lifetimes are likely. However, the feasibility of such a technique has yet to be established through the detection of ground motion following an earthquake using a freely floating balloon. We demonstrate the first detection of an earthquake from a high‐altitude balloon. We explore the dependence of the pressure signal seen by the balloon on parameters such as the magnitude, focal mechanism, location of the earthquake, surface topography, and atmospheric structure. We also show how the signal recorded at the balloon can be used to study the subsurface. Key Points: First detection of a natural earthquake using balloon‐borne infrasound dataRayleigh wave‐induced infrasound dispersion characteristics provide constraints on subsurface velocitiesShallow waveguides, focal mechanism, and subwavelength topographic changes control infrasound amplitude and dispersion by weak earthquakes [ABSTRACT FROM AUTHOR]

On July 11, 2020, NASA's Parker Solar Probe made its third flyby of Venus. The upper hybrid resonance emission was observed below 1,100 km (a first at Venus), revealing electron densities an order of magnitude lower than at solar maximum. These observations are consistent with a substantial variation in the density and structure of the Venusian ionosphere over the Solar Cycle. Plain Language Summary: The planet Venus is in many ways the most Earth‐like planet known and is thus a perfect natural laboratory for understanding what makes Earth‐like planets habitable. It is often thought that Earth's magnetic field is important for life to exist, as it shields our atmosphere from being stripped away to space. If this is true then one might expect that Venus, with no protective magnetic field, would lose more atmosphere when the sun was more active. However, recent studies have shown the opposite to be true. To investigate this, we need measurements of the upper most part of the Venusian atmosphere (the ionosphere, the source of atmospheric escape. On July 11, 2020, NASA's Parker Solar Probe made a close flyby of Venus. During the 7 minutes around the closest approach, one of its scientific instruments detected low‐frequency radio emission of a type naturally generated by planetary ionospheres. By measuring the frequency of this emission, we can directly calculate the density of the ionosphere around Parker, finding it to be far less dense than previous missions have encountered. This supports the theory that the ionosphere of Venus varies substantially over the 11 year solar cycle. Key Points: We report the first detection of upper hybrid resonance emission at Venus, the first in situ measurement of the ionosphere at solar minimumElectron densities were an order of magnitude lower than at solar maximum, and asymmetrically denser toward the terminatorThe Venusian ionosphere varies significantly over the solar cycle, confirming past remote sensing experiments [ABSTRACT FROM AUTHOR]

The Parker Solar Probe (PSP) spacecraft completed its second Venus gravity assist maneuver (VGA2) on December 26, 2019. For a 20 min interval surrounding closest approach, the PSP/FIELDS Radio Frequency Spectrometer (RFS) was set to "burst mode," recording radio spectra from 1.3 to 19.2 MHz at sub‐second cadence. We analyze this burst mode data, searching for signatures of radio frequency "sferic" emission from lightning discharges. During the burst mode interval, only four spectra were observed with strong impulsive signals, and all four could be attributed to saturation of the RFS high gain stage by in situ electrostatic plasma waves. These RFS measurements during VGA2 are consistent with previous non‐detection of radio frequency lightning signals from Venus reported by Gurnett et al. (2001, https://doi.org/10.1038/35053009). Plain Language Summary: The Parker Solar Probe (PSP) studies the physics of the solar wind, using an elliptic solar orbit which brings it much closer to the Sun than any other spacecraft. PSP uses seven Venus flybys to change its orbital trajectory via gravitational assist, lowering the distance of closest solar approach after each flyby. During Venus Flyby 2 in December 2019, the PSP radio receiver was set to a special operating mode, which is sensitive to possible lightning signals from the Venus atmosphere. During the flyby, no lightning signals were detected. This is consistent with previous non‐detection of Venus lightning at radio frequencies reported by Gurnett et al. (2001). Key Points: During the second Parker Solar Probe (PSP) Venus gravity assist, the PSP/FIELDS radio receiver recorded high cadence "burst mode" spectraWe examined the burst mode data for lightning‐associated emission. No lightning events were observed, consistent with prior observationsWe can use this non‐detection to place an upper limit on possible lightning emission from Venus [ABSTRACT FROM AUTHOR]

The present‐day Venusian atmosphere is dry, yet, in its earlier history a significant amount of water evidently existed. One important water loss process comes from the energy and momentum transfer from the solar wind to the atmospheric particles. Here, we used measurements from the Ion Mass Analyzer onboard Venus Express to derive a relation between the power in the upstream solar wind and the power leaving the atmosphere through oxygen ion escape in the Venusian magnetotail. We find that on average 0.01% of the available power is transferred, and that the percentage decreases as the available energy increases. For Mars the trend is similar, but the efficiency is higher. At Earth, the ion escape does not behave similarly, as the ion escape only increases after a threshold in the available energy is reached. These results indicate that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind. Plain Language Summary: Today, there is barely any water on Venus, but presumably a large amount existed in its earlier history. Therefore, the water must have been lost over the course of the Venusian history. An important process for removal of water is escape to space, induced by the interaction between the Venusian atmosphere and the solar wind (a fast stream of particles ejected from the Sun). In this study, we investigated the connection between the energy available in the upstream solar wind and the energy leaving Venus in the form of oxygen ion escape. By characterizing this relation, we investigate how the Venusian atmosphere reacts to changes in the upstream solar wind and how well it protects itself from atmospheric loss caused by the solar wind. We find that the energy transfer decreases as the available upstream energy increases, a trend that is very similar to that found at Mars. However, the Venusian atmosphere seems to absorb less energy from the solar wind than Mars. This indicates that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind. This is important for the understanding of the effect of the solar wind on the Venusian atmospheric evolution. Key Points: The total escaping power from Venus does not increase linearly with increasing available power in the solar windThe coupling coefficient, that is, ratio between power out and in, decreases with increasing solar wind energy fluxThe trend of the coupling coefficient with the upstream parameters for Venus is similar to that of Mars but different from that of Earth [ABSTRACT FROM AUTHOR]

The exploration of the surface geology of Venus has been hampered by its inhospitable conditions and thick and opaque atmosphere. Fundamental properties, such as crustal composition and heterogeneity remain poorly constrained. Multiple analytical techniques are required to better understand its geology. A spectroscopy‐based laboratory study of the emissivity properties of Venus‐relevant igneous rocks, measured at 440°C by Dyar, Helbert, Maturilli, et al. (2020; https://doi.org/10.1029/2020GL090497) shows that the use of multiple atmospheric windows in the 1‐µm region can provide strong constraints on the FeO content of Venus‐relevant igneous rocks, and by extension, the type of igneous rock. These results will help improve our ability to map the surface geology of Venus remotely. Plain Language Summary: The extreme conditions of Venus' atmosphere and surface make exploration by optical techniques difficult. A few successful landed missions and radar observations have helped to understand its surface, which appears to be volcanic in nature. In spite of Venus' global shroud of clouds, some spectral "windows" exist, which are selected wavelengths where the atmosphere and clouds become more transparent. These windows allow us to measure radiation coming off the surface, and differences in the intensity of this radiation can be related to variations in the iron (FeO) content of different rocks, which is also correlated with different types of volcanic rocks. Key points: Venus surface mapping can be advanced using near‐infrared atmospheric windowsMachine learning and laboratory spectra can help to quantify surface composition [ABSTRACT FROM AUTHOR]

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

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

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

A fundamental question for the atmospheric evolution of Venus is how much water‐related material escapes from Venus to space. In this study, we calculate the nonthermal escape of H+ and O+ ions through the Venusian magnetotail and its dependence on the solar cycle. We separate 8 years of data obtained from the ion mass analyzer on Venus Express into solar minimum and maximum. The average escape of H+ decreased from 7.6 · 1024 (solar minimum) to 2.1 · 1024 s−1 (solar maximum), while a smaller decrease was found for O+: 2.9 · 1024 to 2.0 · 1024 s−1. As a result, the H+/O+ flux ratio decreases from 2.6 to 1.1. This implies that the escape of hydrogen and oxygen could have been below the stoichiometric ratio of water for Venus in its early history under the more active Sun. Plain Language Summary: An open issue for the atmospheric evolution of Venus is how the presumably large water content was lost. In this study, we use 8 years of data collected by the ion mass analyzer instrument onboard Venus Express. We investigate the escape of hydrogen H+ and oxygen O+ ions, the components of water, from the Venusian atmosphere to space. If water is escaping from Venus entirely as ions, the hydrogen‐to‐oxygen ratio should be close to 2. We find that the ratio of H+/O+ ion escape is 2.6 for the solar minimum period, while the escape is close to 1‐to‐1 for solar maximum, when the Sun is more active. Thus, Venus is currently on average losing water as ions from its atmosphere. However, in the early history of the solar system, when the Sun was in an even more active state, the escape ratio was probably below the water ratio. This implies that the oxygen did not enrich the atmosphere and surface, and instead hydrogen remained in the Venusian system over its history. Key Points: The escape rate of O+ is almost stable over the solar cycle, while H+ escape rate decreases by a factor of 3.6 from solar minimum to maximumThe H+/O+ escape rate ratio decreases from 2.6 at solar minimum to 1.1 at solar maximumThe historic escape rate has presumably been below the stoichiometric ratio of water [ABSTRACT FROM AUTHOR]