Search

Evidence of chemical disequilibria and other anomalous observations in the Venusian atmosphere motivate the search for life within the planet's temperate clouds. To find signs of a Venusian aerial biosphere, a dedicated astrobiological space mission is required. Venus Life Finder (VLF) missions encompass unique mission concepts with specialized instruments to search for habitability indicators, biosignatures and even life itself. A key in the search for life is direct capture, concentration and visualization of particles of biological potential. Here, we present a short overview of Fluid-Screen (FS) technology, a recent advancement in the dielectrophoretic (DEP) microbial particle capture, concentration and separation. Fluid-Screen is capable of capturing and separating biochemically diverse particles, including multicellular molds, eukaryotic cells, different species of bacteria and even viruses, based on particle dielectric properties. In this short communication, we discuss the possible implementation of Fluid-Screen in the context of the Venus Life Finder (VLF) missions, emphasizing the unique science output of the Fluid-Screen instrument. FS can be coupled with other highly sophisticated instruments such as an autofluorescence microscope or a laser desorption mass spectrometer (LDMS). We discuss possible configurations of Fluid-Screen that upon modification and testing, could be adapted for Venus. We discuss the unique science output of the Fluid-Screen technology that can capture biological particles in their native state and hold them in the focal plane of the microscope for the direct imaging of the captured material. We discuss the challenges for the proposed method posed by the concentrated sulfuric acid environment of Venus' clouds. While Venus' clouds are a particularly challenging environment, other bodies of the solar system, e.g., with liquid water present, might be especially suitable for Fluid-Screen application. [ABSTRACT FROM AUTHOR]

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470 °C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy. Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H 2 O for the obsidian but >250 bar H 2 O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer. Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface. [ABSTRACT FROM AUTHOR]

This work reviews the long-term evolution of the atmosphere of Venus, and modulation of its composition by interior/exterior cycling. The formation and evolution of Venus's atmosphere, leading to contemporary surface conditions, remain hotly debated topics, and involve questions that tie into many disciplines. We explore these various inter-related mechanisms which shaped the evolution of the atmosphere, starting with the volatile sources and sinks. Going from the deep interior to the top of the atmosphere, we describe volcanic outgassing, surface-atmosphere interactions, and atmosphere escape. Furthermore, we address more complex aspects of the history of Venus, including the role of Late Accretion impacts, how magnetic field generation is tied into long-term evolution, and the implications of geochemical and geodynamical feedback cycles for atmospheric evolution. We highlight plausible end-member evolutionary pathways that Venus could have followed, from accretion to its present-day state, based on modeling and observations. In a first scenario, the planet was desiccated by atmospheric escape during the magma ocean phase. In a second scenario, Venus could have harbored surface liquid water for long periods of time, until its temperate climate was destabilized and it entered a runaway greenhouse phase. In a third scenario, Venus's inefficient outgassing could have kept water inside the planet, where hydrogen was trapped in the core and the mantle was oxidized. We discuss existing evidence and future observations/missions required to refine our understanding of the planet's history and of the complex feedback cycles between the interior, surface, and atmosphere that have been operating in the past, present or future of Venus. [ABSTRACT FROM AUTHOR]

Climate models for Venus rely heavily on theoretical modeling and laboratory experimentation due to the extreme surface conditions of the planet and limited in situ surface data. To better explore the relative importance of reactions between the surface and the atmosphere on Venus, we exposed representative volcanic glasses and basaltic minerals to a large‐scale simulation of Venus surface conditions with a realistic atmospheric composition. This study consistend of two experiments of 42 and 80 days that replicated both physical conditions and atmosphere composition derived from available in situ near‐surface data using the Glenn Extreme Environment Rig (GEER) at the NASA Glenn Research Center. These experiments revealed significant reactivity of common Ca‐bearing pyroxenes (diopside and augite) to form anhydrite. Olivine and labradorite showed minimal reactivity. Volcanic glasses, including both natural and synthetic samples, were exceptionally reactive, rapidly forming both anhydrite and thénardite (Na2SO4), as well as transition metal sulfates (i.e., Cu, Cr), halite (NaCl), and sylvite (KCl). Our results document chemical and textural alteration of sample surfaces and provide sufficient evidence for an active sulfur sink on multiple samples, with sulfates as the dominant secondary mineralogy. These experiments suggest likely surface mineralogies and solid phases present on Venus' surface with significant implications for upcoming missions and provide new data for comparison to high‐temperature mineral–gas reactions prevalent on Venus, Earth, and Io. [ABSTRACT FROM AUTHOR]

The cloud layers of Venus are known to have pressures and temperatures comparable to those on Earth, but, at the same time, many details about the environment inside them are unknown. The early consensus was that Venusian clouds are composed of droplets of near concentrated sulfuric acid with very limited water availability; newer models, however, suggest a pH range between −1 and 1, and these imply some form of a neutralizing agent and potentially complex chemical cycles. It is also possible that different populations of cloud particles have different acidities. To answer these questions, we propose an in situ acidity sensor that can statistically determine the acidities of individual cloud droplets from concentrated sulfuric acid (18 M) to deionized water, based on the fluorescence of a pigment that is immobilized in a film and read out using a set of excited LEDs and a camera. Here, we present the preliminary research and prototyping results and suggest a possible design for this sensor. [ABSTRACT FROM AUTHOR]

Life on Venus Expedition (LOVE) Bugs are a proposed family of miniature, featherlight probes for exploring and sensing the Venusian atmosphere. The Bugs carry tiny ThumbSat femtosatellite buses and instruments beneath balloons or flexible parawings. They are designed to descend from 68 to 45 km altitude over several hours because this part of the atmosphere appears to be most welcoming to life as we know it, according to the Venus Life Finder Mission Study. The parawing option is the subject of this work. In order to fit in with larger probe missions, the LOVE-Bug concept is opportunistic. One anticipated opportunity is to be ejected when a "mother probe" needs to deploy a drogue chute for stabilisation through the transonic regime. This work developed an analogy for such a dramatic Venusian ejection by dropping from a high-altitude balloon in Earth's stratosphere. By packaging the payload in a small-diameter low-drag capsule and dropping from 28 km, the vehicle accelerates to supersonic velocity at around 18 km, where the wing is ejected and deployed. A variant of the NASA ParaWing was created by incorporating a drag tail to help to stabilise the wing at extremely high and low velocities. Design, simulation, building, and testing work was carried out, and two flights were flown. The second flight demonstrated successful deployment of the wing in representative Venusian entry conditions. Both flights demonstrated that the ThumbSat performed as required in "space"-type conditions. Recommendations for future work, to qualify the LOVE-Bugs for operation on Venus, are presented. [ABSTRACT FROM AUTHOR]

Mankind often seeks solutions to climate change and environmental crises, but rarely considers the feasibility of outer space to overcome such critical issues. Among many solar geoengineering approaches is stratospheric aerosol injection (SAI) whose concept suggests artificial control of the global temperature by spreading tones of sulfur dioxide into Earth’s stratosphere. Given that the classic ‘technology control dilemma’ represents the central problem of solar geoengineering governance, however, this paper adopts a VenusEarth comparative planetology method by addressing volcanology and atmospheric circulation aspects. An international regulatory framework engaging space law in solar geoengineering governance is consequently presented, which classifies two separate legislations: (1) research-based legislation (comparative planetology and Earth science) and (2) non-research-based legislation (national and international governance, ethical issues, economic factors, military utilization). Further highlighting climate change issues, SAI manifests the Anthropocene and regards Earth’s stratosphere as an “inner environment”, while comparative planetology manifests the Anthropocosmos and regards space as an “outer environment”. This polymorphous consideration of atmospheric and space elements identifies a new approach of climate change techniques. Human relations that concern both environments should examine how social scientists would regard these separate boundaries or perceive them as a mergence between the two major epochs. [ABSTRACT FROM AUTHOR]

The text discusses the second workshop on the potential habitability of the Venus cloud layer, which was held by the Roscosmos/IKI-NASA Joint Science Definition Team for Russia's Venera-D mission. The workshop featured presentations and panel discussions with participants from 36 different countries. The text also mentions the delays in publishing a collection of Venus-relevant papers due to the global COVID pandemic, geopolitical developments, and budget pressures. It highlights the progress made in new discoveries and investigations, including the detection of phosphine in the venusian atmosphere and the observation of geologic signatures of active volcanism. The text concludes by mentioning upcoming missions to Venus and the potential for paradigm-shifting results in the field of astrobiology. [Extracted from the article]

The Venusian clouds originate from the binary condensation of H2SO4 and H2O. The two components strongly interact with each other via chemistry and cloud formation. Previous works adopted sophisticated microphysical approaches to understand the clouds. Here, we show that the observed vapour and cloud distributions on Venus can be well explained by a semi-analytical model. Our model assumes local thermodynamical equilibrium for water vapour but not for sulphuric acid vapour, and includes the feedback of cloud condensation and acidity to vapour distributions. The model predicts strong supersaturation of the H2SO4 vapour above 60 km, consistent with our recent cloud condensation model. The semi-analytical model is 100 times faster than the condensation model and 1000 times faster than the microphysical models. This allows us to quickly explore a large parameter space of the sulphuric acid gas-cloud system. We found that the cloud mass loading in the upper clouds has an opposite response of that in the lower clouds to the vapour mixing ratios in the lower atmosphere. The transport of water vapour influences the cloud acidity in all cloud layers, while the transport of sulphuric acid vapour only dominates in the lower clouds. This cloud model is fast enough to be coupled with the climate models and chemistry models to understand the cloudy atmospheres of Venus and Venus-like extra-solar planets. [ABSTRACT FROM AUTHOR]

The composition, sizes and shapes of particles in the clouds of Venus have previously been studied with a variety of in situ and remote sensor measurements. A number of major questions remain unresolved, however, motivating the development of an exploratory mission that will drop a small probe, instrumented with a single-particle autofluorescence nephelometer (AFN), into Venus's atmosphere. The AFN is specifically designed to address uncertainties associated with the asphericity and complex refractive indices of cloud particles. The AFN projects a collimated, focused, linearly polarized, 440 nm wavelength laser beam through a window of the capsule into the airstream and measures the polarized components of some of the light that is scattered by individual particles that pass through the laser beam. The AFN also measures fluorescence from those particles that contain material that fluoresce when excited at a wavelength of 440 nm and emit at 470–520 nm. Fluorescence is expected from some organic molecules if present in the particles. AFN measurements during probe passage through the Venus clouds are intended to provide constraints on particle number concentration, size, shape, and composition. Hypothesized organics, if present in Venus aerosols, may be detected by the AFN as a precursor to precise identification via future missions. The AFN has been chosen as the primary science instrument for the upcoming Rocket Lab mission to Venus, to search for organic molecules in the cloud particles and constrain the particle composition. [ABSTRACT FROM AUTHOR]

Can a small, lightweight, free-falling sample probe be slowed enough in the Venusian atmosphere to run a 10 min microelectromechanical systems (MEMS) ion gas micro spectrometer, without adding a propulsion systems or explosives and parachutes to the probe mass? To meet this requirement a leading-edge vortex lift (LEVL) autorotating probe design (i.e., maple or sycamore seed shape) has been proposed and evaluated. It has been found that a probe with a total mass of less than 1 kg would allow prolonged flight longer than 15 min. Mathematical modelling and physical scale model testing has been performed to show that this flight time is achievable, allowing MEMS ion gas micro-spectrometer sampling of the Venusian atmosphere. [ABSTRACT FROM AUTHOR]

The planetary missions including the Venus Climate Orbiter 'Akatsuki' provide new information on various atmospheric phenomena. Nevertheless, it is difficult to elucidate their three-dimensional structures globally and continuously only from observations because satellite observations are considerably limited in time and space. We constructed the first 'objective analysis' of Venus' atmosphere by assimilating cloud-top horizontal winds on the dayside from the equator to mid-latitudes, which is frequently obtained from Akatsuki's Ultraviolet Imager (UVI). The three-dimensional structures of thermal tides, found recently to play a crucial role in maintaining the super rotation, are greatly improved by the data assimilation. This result is confirmed by comparison with Akatsuki's temperature observations. The momentum transport caused by the thermal tides and other disturbances are also modified by the wind assimilation and agrees well with those estimated from the UVI observations. The assimilated dataset is reliable and will be open to the public along with the Akatsuki observations for further investigation of Venus' atmospheric phenomena. [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]

In-situ exploration of Venus is challenging due to its severe environment, which is benign (∼25 °C and 1 bar) at an altitude of 55 km, but rapidly becomes hostile at lower altitudes. The temperature increases to ∼465 °C, and pressure reaches 90 bars at the surface. These conditions have limited in-situ missions to high altitude balloons at 55 km that survived only 48 h. High-altitude balloon missions are stymied by the opaqueness of the Venusian clouds and constant altitude. Long-duration, extended range variable-altitude balloons covering below the clouds could enhance the science capabilities of the missions by measuring chemical species, isotopes and atmospheric flow patterns in and underneath the clouds. A new energy storage system tolerant to the high temperatures at low altitudes is needed to support such a balloon. A novel variable altitude balloon architecture with an extended range of 55–20 km (VAB-X) was developed under the NASA Innovative and Advanced Concepts (NIAC) program and is described here. The architecture comprises a high-temperature tolerant balloon and photovoltaic array for providing spacecraft power, a reversible solid oxide fuel (SOFC) for low-altitude power and fuel regeneration, and reversible metal hydride (MH) for hydrogen storage. Hydrogen is used for the buoyancy and altitude control of the zero-pressure balloon and as fuel for SOFC. Water brought from Earth can replenish the hydrogen lost to leaks during the mission. Preliminary analyses reveal the efficacy of the architecture for long-term Venus exploration over 55-20 km altitude, with a high proportion (∼20%) of the total suspended mass (>20 kg) available for science payload. • A new variable altitude and long-life balloon architecture for Venus atmospheric missions across and below Venus clouds. • First hydrogen-based balloon for Venus Aerial missions and novel use of hydrogen for both buoyancy and power. • Generation of hydrogen with SOFC at high altitude, storage in metal hydrides use as fuel for SOFC at low altitude. • Balloon performance model for balloon dynamics in the Venus atmosphere. • Zero pressure variable-altitude H 2 balloon with hydrogen storage and SOFC for long-term exploration of Venus deep atmosphere. [ABSTRACT FROM AUTHOR]

The latest version of the HITRAN molecular spectroscopic data base, HITRAN2020, has recently been released featuring many updates, including line-by-line broadening parameters (and their temperature dependence) appropriate for the dominant constituents of planetary atmospheres. In this work, line shape codes suitable for calculating microwave spectra have been implemented within the HITRAN Application Programming Interface (HAPI). These new additions allow for spectroscopic calculations of microwave absorbing species pertinent to current and future studies of the atmospheres of Jupiter and Venus, and more generally for the atmospheres of gas giants and rocky planets. The inversion spectrum of the NH3 molecule broadened by H2, He, and H2O dominates the microwave region of Jupiter, whereas for Venus, accurate spectroscopic data of SO2 broadened by CO2 are necessary in order to determine its significance, if any, on the reported detection of PH3 in the Venusian upper cloud deck. Comparisons have been made to available microwave laboratory opacities and the following results illustrate that HITRAN data can be used in conjunction with HAPI to reproduce the existing experimental measurements and provide reliable calculation of planetary opacities. Users should be mindful regarding selection of appropriate parameters in HITRAN and selecting suitable line shape functions in HAPI, depending on the spectral region, target molecular species, as well as ambient chemical and thermodynamic conditions. [ABSTRACT FROM AUTHOR]

New analysis is presented of the 1.1 mm wavelength absorption lines in Venus' atmosphere that suggested the presence of phosphine. We retrieve a sulphur dioxide observation from the JCMT archive that was simultaneous within a few days of the PH3 1-0 spectrum obtained in 2017 June, and demonstrate via a radiative transfer calculation that contamination of PH3 by SO2 was ≈10 per cent. We also present ALMA 2019 spectra of PH3 1-0 and an SO2 transition acquired simultaneously, and infer that SO2 line-contamination was ≲2 per cent (for the least-noisy half of the planetary disc). The contamination-subtracted ALMA and JCMT spectra (of 6–8σ sigma confidence) are now consistent with similar absorption-depths at the two epochs. The two values span −1.9(±0.2) 10−4 of the continuum signal (which was re-estimated for ALMA), albeit for differing planetary areas. This suggests that the abundance attributed to phosphine in Venus' atmosphere was broadly similar in 2017 and 2019. [ABSTRACT FROM AUTHOR]

Polysulfur species have been proposed to be the unknown near-UV absorber in the atmosphere of Venus. Recent work argues that photolysis of one of the (SO)2 isomers, cis-OSSO, directly yields S2 with a branching ratio of about 10%. If correct, this pathway dominates polysulfur formation by several orders of magnitude, and by addition reactions yields significant quantities of S3, S4, and S8. We report here the results of high-level ab-initio quantum-chemistry computations that demonstrate that S2 is not a product in cis-OSSO photolysis. Instead, we establish a novel mechanism in which S2 is formed in a two-step process. Firstly, the intermediate S2O is produced by the coupling between the S and Cl atmospheric chemistries (in particular, SO reaction with ClS) and in a lesser extension by O-abstraction reactions from cis-OSSO. Secondly, S2O reacts with SO. This modified chemistry yields S2 and subsequent polysulfur abundances comparable to the photolytic cis-OSSO mechanism through a more plausible pathway. Ab initio quantification of the photodissociations at play fills a critical data void in current atmospheric models of Venus. Polysulfur compounds have been ascribed as the unknown near-UV absorbers in Venusian atmosphere and play a key role in the sulfur chemical cycle of this planet. Here, authors establish their production from (SO)2 on the grounds of quantifications of photochemical and thermal pathways involved in the sulfur chemical cycle of the planet. [ABSTRACT FROM AUTHOR]

I Dr. Sara Seager: i My team was working through all possible biosignature gases on exoplanets, and we did not know that an astronomer across the world, Professor Jane Greaves in the United Kingdom, was also thinking about phosphine as a biosignature gas. There is a bit of tension between the two: the internal coronagraph telescope is good to search for new planets because it can quickly point in new directions, but Starshade wins out over the internal coronagraph by its throughput and ability to observe a broad wavelength spectrum, all in one observation. That paper, on how to observe exoplanet atmospheres by what I called "transmission spectroscopy", led to the main way we observe exoplanet atmospheres today, so it is one of my proudest achievements. I Dr. Sara Seager: i Back in the old days, there were a couple of transiting exoplanets, but no one had ever found an exoplanet by the transit technique itself, such as is common today by the wide-field MIT-led NASA Mission TESS and wide-field ground-based surveys. [Extracted from the article]

Mounting evidence of chemical disequilibria in the Venusian atmosphere has heightened interest in the search for life within the planet's cloud decks. Balloon systems are currently considered to be the superior class of aerial platform for extended atmospheric sampling within the clouds, providing the highest ratio of science return to risk. Balloon-based aerial platform designs depend heavily on payload mass and target altitudes. We present options for constant- and variable-altitude balloon systems designed to carry out science operations inside the Venusian cloud decks. The Venus Life Finder (VLF) mission study proposes a series of missions that require extended in situ analysis of Venus cloud material. We provide an overview of a representative mission architecture, as well as gondola designs to accommodate a VLF instrument suite. Current architecture asserts a launch date of 30 July 2026, which would place an orbiter and entry vehicle at Venus as early as November 29 of that same year. [ABSTRACT FROM AUTHOR]

Venus is known for its extreme surface temperature and its sulfuric acid clouds. But the cloud layers on Venus have similar temperature and pressure conditions to those on the surface of Earth and are conjectured to be a possible habitat for microscopic life forms. We propose a mission concept to explore the clouds of Venus for up to 30 days to evaluate habitability and search for signs of life. The baseline mission targets a 2026 launch opportunity. A super-pressure variable float altitude balloon aerobot cycles between the altitudes of 48 and 60 km, i.e., primarily traversing the lower, middle, and part of the upper cloud layers. The instrument suite is carried by a gondola design derived from the Pioneer Venus Large Probe pressure vessel. The aerobot transmits data via an orbiter relay combined with a direct-to-Earth link. The orbiter is captured into a 6-h retrograde orbit with a low, roughly 170-degree, inclination. The total mass of the orbiter and entry probe is estimated to be 640 kg. An alternate concept for a constant float altitude balloon is also discussed as a lower complexity option compared to the variable float altitude version. The proposed mission would complement other planned missions and could help elucidate the limits of habitability and the role of unknown chemistry or possibly life itself in the Venus atmosphere. [ABSTRACT FROM AUTHOR]

Power fluctuations are observed on radio signals propagating through the Venus atmosphere. These scintillations, due to fluctuations in refractive index, are particularly strong between 56 and 72 km altitude where the strong convective stability favors gravity wave propagation. We examine low-latitude X-band radio occultation experiments performed by the Akatsuki spacecraft to assess the statistical variability of these scintillations. The observed root-mean-square scintillation amplitudes at a given altitude vary by a factor of about 3. Part of this range is due to the different geometry of the occultations: the corresponding variations in refractive structure constant at 60-70 km altitude span a factor of ∼2. These propagation characteristics may influence the optimization of the two-way radio link for the DAVINCI mission currently in development. • Examines scintillations in Akatsuki Radio Occultations. • Changes of as much as 15 dB of signal power in 1 s are seen. • Scintillation amplitudes at a given altitude vary by a factor of about 3. [ABSTRACT FROM AUTHOR]

The first non-Earth aerobraking experiment occurred in 1993 as part of the Magellan satellite's mission to Venus. Magellan reduced its orbit from elliptical to nearly circular over a span of 70 Earth days by leveraging the non-conservative force of aerodynamic drag to reduce its orbital energy via transiting the upper region of Venus' sensible atmosphere. First tested with the Hiten probe in the Earth-Moon system in 1991, the subsequent Magellan experiment helped prove the viability of aerobraking for planetary missions and paved the way for its implementation in Mars missions starting in the late 1990s and the 2014 Venus Express mission. This paper, for the first time in literature, investigates the Magellan aerobraking experiment from the perspective of both 3- and 6-degree-of-freedom analysis. Multiple atmospheric density models are considered, as well as J 4 gravitational perturbations in order to understand the complexity and sensitivity of numerous aerobraking maneuvers in the thick Venusian atmosphere. Alternative satellites are also studied to ascertain their capability of maintaining the Magellan aerobraking flight profile. So as to examine a wide range of vehicle mass and drag reference area, the Hubble Space Telescope (HST) and Hiten satellites are modeled and their aerobraking performance analyzed for the hypothetical case of Venus orbital operations. When reconstructing the historical Magellan aerobraking maneuvers, 3DOF and 6DOF analysis yielded minimal trajectory deviation with the Magellan and Hiten models, while more significant deviation was experienced with the larger HST model. Both 3DOF and 6DOF analyses also reveal the sensitivity of the atmospheric density model and indicate a higher fidelity gravity model is necessary for Venusian aerobraking modeling, planning, and analysis. • 6DOF modeling achieved improved agreement with the Magellan historical data than the 3DOF simulations. • A high-fidelity gravity model of at least J4 is necessary for Venusian aerobraking modeling, planning, and analysis. • The 1968 high-density and Venus GRAM models enabled the greatest agreement between the 3DOF model and historical data. • Satellites with small drag reference areas encounter lower aerodynamic torques during aerobraking. [ABSTRACT FROM AUTHOR]

Power fluctuations have been noted on radio signals propagating through the Venus atmosphere since the very first descent probe there (Venera 4) and have been observed as a routine feature in radio occultations, where the grazing ray geometry amplifies the effect of refractive scattering structures. Motivated by DAVINCI and other missions currently in development, a physical model of refraction variations in the Venus atmosphere is developed using the VEGA-2 high-resolution temperature profile down to the surface and other data, which suggest several distinct layers of more intense scattering. The resultant modeled radio scintillations are compared with observed scintillations and assessed for the DAVINCI relay link. High-time-resolution radio signal power measurements on the DAVINCI radio link promise to be an interesting probe of the Venus atmosphere. • Reviews historical observations of radio power fluctuations in turbulent Venus atmosphere. • Develops first-principles model based on temperature observations. • Applies model to make predictions for DAVINCI mission under development. [ABSTRACT FROM AUTHOR]

Meteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5 × to 2.5 × higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun. • We use physics-based modelling to understand the properties of meteors in the upper atmosphere of Venus and to compare meteor survey efficiency from Earth orbit and from Venus orbit. • Venus meteors would be brighter and shorter-lived than Earth meteors, due to different atmospheric density scale heights. • Assuming similar meteoroid populations at the two planets, orbital meteor surveys would detect 1.5 × –2.5 × more meteors per hour at Venus than at Earth. [ABSTRACT FROM AUTHOR]

Life in the clouds of Venus, if present in sufficiently high abundance, must be affecting the atmospheric chemistry. It has been proposed that abundant Venusian life could obtain energy from its environment using three possible sulfur energy-metabolisms. These metabolisms raise the possibility of Venus's enigmatic cloud-layer SO2-depletion being caused by life. We here couple each proposed energy-metabolism to a photochemical-kinetics code and self-consistently predict the composition of Venus's atmosphere under the scenario that life produces the observed SO2-depletion. Using this photo-bio-chemical kinetics code, we show that all three metabolisms can produce SO2-depletions, but do so by violating other observational constraints on Venus's atmospheric chemistry. We calculate the maximum possible biomass density of sulfur-metabolising life in the clouds, before violating observational constraints, to be ~10−5 − 10−3 mg m−3. The methods employed are equally applicable to aerial biospheres on Venus-like exoplanets, planets that are optimally poised for atmospheric characterisation in the near future. The metabolisms proposed for hypothetical life in the clouds of Venus cannot explain the planet's atmospheric chemistry and thus a limit can be placed on the maximum allowed biomass. [ABSTRACT FROM AUTHOR]

Recent and past observations of chemical and physical peculiarities in the atmosphere of Venus have renewed speculations about the existence of life in its clouds. To find signs of Venusian life, a dedicated astrobiological space exploration mission is required, and for this reason the Venus Life Finder mission is currently being prepared. A Venus Life Finder mission will require dedicated and specialized instruments to hunt for biosignatures and habitability indicators. In this contribution, we present the ORIGIN space instrument, a laser desorption/laser ablation ionization mass spectrometer. This instrument is designed to detect large, non-volatile molecules, specifically biomolecules such as amino acids and lipids. At the same time, it can also be used in ablation mode for elemental composition analysis. Recent studies with this space prototype instrument of amino acids, polycyclic aromatic hydrocarbons, lipids, salts, metals, sulphur isotopes, and microbial elemental composition are discussed in the context of studies of biosignatures and habitability indicators in Venus's atmosphere. The implementation of the ORIGIN instrument into a Venus Life Finder mission is discussed, emphasizing the low weight and low power consumption of the instrument. An instrument design and sample handling system are presented that make optimal use of the capabilities of this instrument. ORIGIN is a highly versatile instrument with proven capabilities to investigate and potentially resolve many of the outstanding questions about the atmosphere of Venus and the presence of life in its clouds. [ABSTRACT FROM AUTHOR]

In order to resolve discrepancy between recent observational and numerical studies on the thermal tides in the Venusian atmosphere, we investigated by means of a general circulation model how the thermal tides are affected by the static stability in and above the upper cloud layer by using three different distributions of the static stability. The results show that the vertical structure of the semidiurnal tide, which propagates vertically, is strongly affected by the static stability. The diurnal tide, which has an equivalent barotropic structure in 62–73 km altitudes, becomes weaker with the higher static stability although its vertical structure is almost unchanged. The horizontal distribution of the thermal tides with the realistic static stability distribution, which is consistent with radio occultation measurements, agrees with the observations at the cloud top. The meridional angular momentum flux associated with the thermal tides is equatorward in low latitudes near the altitude where the equatorial zonal‐mean wind takes its maximum. This result is consistent with the recent Akatsuki UVI observations, suggesting that the thermal tides could contribute to the maintenance of the superrotation in the equatorial region near the cloud top. In the most realistic case, the zonal‐mean zonal wind is effectively accelerated at rates of 0.2–0.5 m s−1 day−1 in low latitudes at altitudes of 52–76 km by both the meridional and vertical angular momentum transports. The thermal tides also induce significant meridional heat flux, which cannot be ignored in the dynamical effect on the zonal‐mean zonal wind. Plain Language Summary: Thermal tides are planetary‐scale atmospheric waves excited by the solar heating and fixed to the solar motion. These waves with the zonal wavenumbers of 1 and 2 are called "diurnal tide" and "semidiurnal tide," respectively. In the Venusian atmosphere, the most part of solar energy is absorbed in the cloud layer in 45–70 km altitudes, so that the thermal tides are strongly excited in this layer. There is a discrepancy between results obtained by recent observations and those by numerical simulations of the thermal tides. In this study, we resolve this discrepancy by investigating how the thermal tides depend on the temperature distribution in and above the cloud layer. The result shows that the temperature distribution plays important roles on the vertical structure of the semidiurnal tide. Therefore, it is crucially important to adopt a correct temperature distribution in the numerical model in order to reproduce realistic thermal tides consistent with the recent observations. Further, it is found that the thermal tides transport angular momentum meridionally and vertically and heat meridionally. Through this angular momentum transport, the thermal tides could contribute to the maintenance of the superrotation in the equatorial region near the cloud top. Key Points: A realistic structure of the Venusian thermal tide consistent with recent observations is reproduced by improving the static stabilityThe thermal tide induces meridional angular momentum and heat transports as well as vertical angular momentum transport in the cloud layerThe thermal tide could contribute to the superrotation through not only the thermal tide mechanism but also the meridional circulation one [ABSTRACT FROM AUTHOR]

Three recently approved space missions are headed towards Venus, to help answer major questions about Venus atmosphere and geology. However, many existing questions cannot be properly addressed without direct in situ measurements from Venus surface or within the atmosphere. To this end, flapping wing vehicle concept is selected, optimized for Venus atmospheric flight, and evaluated using energy efficiency as performance criteria. Flapping wing vehicle computational model is derived based on discrete variational mechanics and quasi-steady aerodynamics, with all relevant aerodynamic phenomena included. Flapping wing vehicle computational model is then embedded within optimization algorithm, which is utilized to obtain energy efficient flapping patterns for forward flight in Venus surface atmospheric conditions. Numerical optimization is performed for different neutrally buoyant configurations, with wingspan ranging from 10 mm to 1 m. Different forward velocities are used as well, where maximum velocity is limited by an advance ratio of 0.5. Bumblebee and hummingbird-sized vehicles, with a wingspan of 30 mm and 30 cm, are selected as the most representative test cases and thoroughly studied. It is proved that flapping wing propulsion is a feasible and effective concept for Venus exploration purposes. Finally, based on a comparison of the selected test cases, general conclusions are drawn on the flapping wing dynamics and flight mechanics in the Venus atmosphere. Significant difference in the propulsion mechanism has been observed, based on the aerial vehicle size. In order to maximize propulsive efficiency, the smaller vehicle mostly exploited aerodynamic forces related to the leading edge vortex, while the larger vehicle relied more on added mass and rotational forces. • Flapping wing vehicles can be used for Venus atmospheric flight and exploration. • Quasi-steady forward flight model can be used to model Venus flapping flight. • Flapping wing dynamics can be efficiently optimized using DMOC framework. • Added mass and rotational forces have strong impact on Venus flapping flight. [ABSTRACT FROM AUTHOR]

The potential detection of ppb levels phosphine (PH3) in the clouds of Venus through millimeter-wavelength astronomical observations is extremely surprising as PH3 is an unexpected component of an oxidized environment of Venus. A thorough analysis of potential sources suggests that no known process in the consensus model of Venus' atmosphere or geology could produce PH3 at anywhere near the observed abundance. Therefore, if the presence of PH3 in Venus' atmosphere is confirmed, it is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The source of atmospheric PH3 could be unknown geo- or photochemistry, which would imply that the consensus on Venus' chemistry is significantly incomplete. An even more extreme possibility is that strictly aerial microbial biosphere produces PH3. This paper summarizes the Venusian PH3 discovery and the scientific debate that arose since the original candidate detection one year ago. [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]

We present more than 250,000 wind vectors derived from the visible (513 nm) images captured by the Venus Monitoring Camera (VMC) onboard ESA's Venus Express orbiter in the Southern hemisphere from 01 July 2007 to 29 January 2013. From comparison to the wind velocity derived from tracking of the descent probes, these measurements correspond to 60 ± 3 km altitude, being between two levels 70 ± 2 km and 55 ± 2 km, probed by VMC in ultraviolet (UV) (365 nm) and NIR (965 nm) channels, respectively. The mean zonal wind suggests retrograde circulation with mean zonal wind speed decreasing from 76.5 to 61.5 m/s at 30°–65°S. In low latitudes, 10–20°S, it increased to 82 m/s over the course of the mission. The mean zonal flow depends on local solar time and latitude and is affected by the large‐scale topography. The meridional winds indicated equatorward flow of up to 7 m/s in the middle and low cloud opposite to that derived from simultaneous UV observations at the cloud top. Plain Language Summary: Dynamics of the Venus atmosphere is dominated by a strong zonal retrograde circulation called "superrotation." The physical mechanisms maintaining this unique regime are poorly understood due to insufficient observational data. For about eight years, the Venus Monitoring Camera onboard ESA's Venus Express orbiter monitored motions of the cloud features in three spectral ranges: ultraviolet (UV) (365 nm), visible (513 nm), and near‐infrared (915 nm). These wavelengths probed different altitudes: 70 ± 2 km, 60 ± 3 km, and 55 ± 2 km correspondingly, thus providing wind field tomography. In this paper, we present more than 250,000 wind vectors derived from the visible images. The results suggest decrease of the retrograde mean zonal wind speed from 76.5 to 61.5 m/s at 30°–65°S, and its increase up to 82 m/s at 10–20°S and show pronounced variations with local solar time, latitude, and surface topography. Interestingly, the meridional winds indicate equatorward flow of up to 7 m/s in the deep cloud opposite to that previously derived from UV images at the cloud top. Key Points: More than 250,000 wind vectors at 57–63 km altitude were derived from the images taken by the Venus Monitoring Camera /Venus Express visible (513 nm) channelMean zonal wind speed accelerated by ∼18.5 m/s at 30 ± 5°S over 8 Venusian yearsZonal wind speed decreased from 85 m/s at the equator to 35 m/s at 80°S, meridional wind of up to 7 m/s velocity is directed equatorward [ABSTRACT FROM AUTHOR]

The 4‐day and 5‐day waves observed at the cloud top in the Venus atmosphere are expected to play important roles in the maintenance of the general circulation. However, they have not been reproduced in Venus general circulation models (GCMs) so far, and their structures and excitation mechanisms remain poorly understood. Using an improved Venus GCM, we succeeded in reproducing the planetary‐scale 3.3‐day and 5.8‐day waves, which are considered to correspond to the 4‐day and 5‐day waves, respectively. We also obtained the 4.8‐day wave, whose structure is similar to that of the 5.8‐day wave. The three‐dimensional structures of these waves consist of a Kelvin wave in low latitudes and one or two Rossby waves in mid‐ and high latitudes that are connected at the critical latitudes. This fact indicates that they are excited by the Rossby‐Kelvin instability. The Kelvin mode of the 3.3‐day wave could be observed at the cloud top, while those of the 5.8‐day and 4.8‐day waves cannot be observed due to the critical levels. The mid‐latitude Rossby mode of the 5.8‐day wave is dominated by mid‐latitude vortices symmetric about the equator at the cloud top; this result is quite consistent with the observations. The equatorward angular momentum flux induced by these waves could contribute to the Venus superrotation. The Rossby modes of the 5.8‐day and 4.8‐day waves have baroclinic structures in the cloud layer inducing significant poleward heat flux. The planetary‐scale structures symmetric about the equator observed in the Venus atmosphere could be explained by these waves. Plain Language Summary: Planetary‐scale waves called 4‐day and 5‐day waves have been observed in the Venus atmosphere, which are expected to play important roles in the global atmospheric motions. However, they have not been reproduced in numerical models so far, and hence their three‐dimensional structures remain completely unknown. In the present study, we found planetary‐scale waves with periods of 3.3, 5.8, and 4.8 days in our numerical simulation. The 3.3‐day and 5.8‐day waves are considered to correspond to the 4‐day and 5‐day waves observed in the Venus atmosphere. The three‐dimensional structures of these waves, in which an equatorial wave and one or two mid‐ and high‐latitude vortex waves are connected, indicate that the waves are excited by dynamical instability called Rossby‐Kelvin instability. The mid‐latitude wave of the 5.8‐day wave is dominated by vortices symmetric about the equator at 70 km altitude, which are quite consistent with the observations. The equatorward angular momentum transport and the poleward heat transport are induced by the 5.8‐day and 4.8‐day waves, suggesting that these waves could contribute to the maintenance of the fast zonal winds on Venus. The observed planetary‐scale structures symmetric about the equator such as cloud patterns could be explained by these waves. Key Points: We succeeded in reproducing the 4‐day and 5‐day waves observed at the Venus cloud top, which are excited by the Rossby‐Kelvin instabilityThese waves induce the equatorward angular momentum flux, which could contribute to the maintenance of the Venus superrotationThese waves could relate to the planetary‐scale structures symmetric about the equator widely observed in the Venus atmosphere [ABSTRACT FROM AUTHOR]

The recently discovered near-Earth asteroid 2021 PH27 has the shortest orbital period of all known asteroids. It cannot be excluded that 2021 PH27 is also an active asteroid, as (3200) Phaethon. We intend to estimate the consequences of this hypothesis, although testing is difficult with ground-based observations during perihelion passages, due to low solar elongation. Assuming a surface activity similar to that of Phaethon, an increase in brightness of about 1.4 mag can be estimated. Since it is an asteroid with a minimum orbit intersection distance of 0.014660 ± 0.000034 au with Venus, 2021 PH27 could be the equivalent of Phaethon for the Earth and be the progenitor body of a Venusian meteor shower. A good opportunity to observe the hypothetical fireballs in Venus's atmosphere will take place on the days around 2023 June 7, when Venus will pass at the minimum distance from the nominal orbit of 2021 PH27. Another favourable date will be 2026 July 5. Finally, on 2022 March 28, the asteroid will also be at the maximum Sun elongation of about 52 |${_{.}^{\circ}}$| 3 and at the aphelion of its orbit, the most favourable configuration to characterize it from the physical point of view with photometric, polarimetric, and spectroscopic observations. [ABSTRACT FROM AUTHOR]

Distributions of temperature and static stability in the Venus atmosphere consistent with recent radio occultation measurements are reproduced using a general circulation model. A low‐stability layer is maintained at low‐ and mid‐latitudes at 50–60 km altitude and is sandwiched by high‐ and moderate‐stability layers extending above 60 and below 50 km, respectively. In the polar region, the low‐stability layer is located at 46–63 km altitude and the relatively low‐stability layer is also found at 40–46 km altitude. To investigate how these thermal structures form, we examine the dynamical effects of the atmospheric motions on the static stability below 65 km altitude. The results show that the heat transports due to the mean meridional circulation and disturbances are important in low‐latitudes. The mid‐ and high‐latitudes above ∼47 km are destabilized by radiative processes and stabilized by the disturbances, which are mainly associated with baroclinic Rossby‐type waves. Below ∼47 km altitude, the polar region is destabilized by the dynamical processes which induce the appreciable equatorward heat transport, which might be related to Rossby waves in the sub‐cloud region, although the suppression of convective adjustment at cloud heights leads to stabilization at 43–47 km. Plain Language Summary: The thermal structure of the Venus atmosphere, namely distributions of temperature and static stability, is very important because it represents a degree of atmospheric stratification. Furthermore, it is strongly related to the heat transport due to the atmospheric dynamics such as mean meridional circulation and disturbances. In this study, the temperature and static stability distributions revealed by recent radio occultation measurements were well reproduced by a Venus general circulation model. We examined dynamical effects due to the mean meridional circulation and disturbances on static stability to elucidate how the thermal structures were maintained. At low‐latitudes, the mean meridional circulation and disturbances play an important role in maintaining the static stability distribution. At mid‐ and high‐latitudes, the static stability distribution is strongly affected by planetary‐scale atmospheric waves. In addition, we clarified the characteristics of the waves and proposed their origins. The structures and characteristics of the mean meridional circulation and disturbances shown in this study will help us to investigate how the super‐rotation is maintained in terms of their momentum transport. Key Points: The thermal structure of the Venus atmosphere reproduced with a general circulation model is consistent with recent radio occultation measurementsHeat transport due to disturbances strongly affects the thermal structure at mid‐ and high‐latitudesEquatorward heat transport induced by the interaction between Rossby waves produces a deep low‐stability layer in the polar region [ABSTRACT FROM AUTHOR]

The main observations of 1761 by M. Lomonossov and those that followed are recalled by extending the discussion to other remarkable visual observations of the passages, then with more and more powerful imagers producing images in profusion. The modern treatment of parasitic effects is briefly recalled by focusing on the expert observation of 1761 which has recently been widely commented on and criticized. It included a spurious effect called the "black drop effect". The shell or aureole or atmospheric ring of Venus observed outside the solar disk is considered with reference to the today parameters of the Venus atmosphere. The contacts during the transit are discussed taking into account effects of scattering, absorption, and the dominant effects of the refraction at the small angular distances found to be comparable to a fraction of the angular dimension of the planet. Modern observations of the 2004 and the 2012 transit are tentatively discussed to elucidate what is the arc of Lomonossov. [ABSTRACT FROM AUTHOR]

The atmosphere of Venus remains mysterious, with many outstanding chemical connundra. These include the unexpected presence of ~10 ppm O2 in the cloud layers, an unknown composition of large particles in the lower cloud layers, and hard to explain measured vertical abundance profiles of SO2 and H2O. We propose a hypothesis for the chemistry in the clouds that largely addresses all of the above anomalies. We include ammonia (NH3), a key component that has been tentatively detected both by the Venera 8 and Pioneer Venus probes. NH3 dissolves in some of the sulfuric acid cloud droplets, effectively neutralizing the acid and trapping dissolved SO2 as ammonium sulfite salts. This trapping of SO2 in the clouds, together with the release of SO2 below the clouds as the droplets settle out to higher temperatures, explains the vertical SO2 abundance anomaly. A consequence of the presence of NH3 is that some Venus cloud droplets must be semisolid ammonium salt slurries, with a pH of ~1, which matches Earth acidophile environments, rather than concentrated sulfuric acid. The source of NH3 is unknown but could involve biological production; if so, then the most energy-efficient NH3-producing reaction also creates O2, explaining the detection of O2 in the cloud layers. Our model therefore predicts that the clouds are more habitable than previously thought, and may be inhabited. Unlike prior atmospheric models, ours does not require forced chemical constraints to match the data. Our hypothesis, guided by existing observations, can be tested by new Venus in situ measurements. [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]

Since the invention of the telescope, observers of Venus have often reported irregularities in the shape of the planet's terminator and cusps. Some of these, such as terminator undulations, might be easily ascribed to poor seeing conditions; others, such as cusp extensions near inferior conjunction, are undoubtedly real and evidence of Venus's atmosphere. This paper considers a third category: detached points of light recorded by several observers at the cusps of the planet, explained by some as high mountain peaks catching the sunlight. Among those who argued for the existence of such mountains was Johann Schrater, a stance that brought him into conflict with the views of William Herschel. Nowadays the 'ghost mountains of Venus' are seen for what they are: an illusion encouraged by a growing belief in the plurality of Earth-like worlds. [ABSTRACT FROM AUTHOR]

The article covers the concept and historical aspects of development of automated space stations Luna-16, Luna-17, and Venera-7, which for the first time in the world successfully completed outstanding scientific programs. They opened the way for the world scientific community to study the Moon and the planets of the Solar System, providing invaluable experience for the development of the next-generation space missions. [ABSTRACT FROM AUTHOR]