Volcanically extruded phosphides as an abiotic source of Venusian phosphine

We hypothesize that trace amounts of phosphides formed in the mantle are a plausible abiotic source of the Venusian phosphine observed by Greaves et al. [Nat. Astron., https://doi.org/10.1038/s41550-020-1174-4 (2020)]. In this hypothesis, small amounts of phosphides (P3− bound in metals such as iron), sourced from a deep mantle, are brought to the surface by volcanism. They are then ejected into the atmosphere in the form of volcanic dust by explosive volcanic eruptions, which were invoked by others to explain the episodic changes of sulfur dioxide seen in the atmosphere [Esposito, Science 223, 1072–1074 (1984)]. There they react with sulfuric acid in the aerosol layer to form phosphine (2 P3− + 3H2SO4 = 2PH3 + 3SO42-). We take issue with the conclusion of Bains et al. [arXiv:2009.06499 (2020)] that the volcanic rates for such a mechanism would have to be implausibly high. We consider a mantle with the redox state similar to the Earth, magma originating deep in the mantle—a likely scenario for the origin of plume volcanism on Venus—and episodically high but plausible rates of volcanism on a Venus bereft of plate tectonics. We conclude that volcanism could supply an adequate amount of phosphide to produce phosphine. Our conclusion is supported by remote sensing observations of the Venusian atmosphere and surface that have been interpreted as indicative of currently active volcanism.

The Case (or Not) for Life in the Venusian Clouds

The possible detection of the biomarker of phosphine as reported by Greaves et al. in the Venusian atmosphere stirred much excitement in the astrobiology community. While many in the community are adamant that the environmental conditions in the Venusian atmosphere are too extreme for life to exist, others point to the claimed detection of a convincing biomarker, the conjecture that early Venus was doubtlessly habitable, and any Venusian life might have adapted by natural selection to the harsh conditions in the Venusian clouds after the surface became uninhabitable. Here, I first briefly characterize the environmental conditions in the lower Venusian atmosphere and outline what challenges a biosphere would face to thrive there, and how some of these obstacles for life could possibly have been overcome. Then, I discuss the significance of the possible detection of phosphine and what it means (and does not mean) and provide an assessment on whether life may exist in the temperate cloud layer of the Venusian atmosphere or not.

Equilibrium compositions in gas phase systems

A new method of calculation of equilibrium compositions of single-phase multicomponent systems in a wide range of temperatures, pressures, and elemental compositions is proposed. It is based on the minimization of the integral characteristic of the slope of the thermodynamic potential surface in the space of coordinates of chemical reactions. The proposed algorithm is applied to the definition of area of the thermodynamic stability of freons in volcanic gases and to the construction of the equilibrium profiles of the height distribution of sulphur-containing components of Venusian atmosphere.

Investigation of the Ballistic Descent Mode for a Maneuverable Lander to the Venus Surface

At present, various projects to continue fundamental investigations of Venus are considered in Russia and abroad. It means that the issue of developing a landing module to reach the surface of the planet becomes topical, as the module might provide access to the regions most attractive in terms of research. We propose to use a landing module of the lifting body type, which, as compared to a ballistic class module, is not unacceptably complicated in terms of design and at the same time features a lift-to-drag ratio adequate for solving manoeuvring problems arising in the process of descent into the Venusian atmosphere to reach the target landing area. We consider potential descent trajectories available to a landing module of this type, including the possibility of performing a maximum lateral manoeuvre; we took into consideration its long-period trajectories characterised by multiple re-entries into the dense atmosphere and compared these trajectories to the descent trajectory of a conventional ballistic class landing module. We show that using a manoeuvrable craft expands the selection of potential landing regions, as well as reduces loads and broadens the scope of scientific problems to be solved and studies to be undertaken

Exploring the variability of the venusian atmosphere above the clouds with the IPSL Venus GCM

<p>To investigate the amount of data recently acquired by the Venus Express (VEx) and Akatsuki missions as well as from ground-based telescopes, Venus Global Climate Models (GCM) are powerful tools. Our understanding of the Venusian climate has increased with recent progresses with these models.<br>The IPSL Venus GCM has been used recently to investigate all regions of the Venusian atmosphere, as it covers the surface up to the thermosphere (150 km). It involves a photochemical module with a simplified cloud scheme that enables the study of the composition and the coupling with the upper atmosphere, where composition plays a crucial role on the non-LTE and EUV heating processes. Other relevant physical processes in the thermosphere (e.g. molecular diffusion and thermal conduction) are taken into account. Below 100 km, the infrared energy budget is computed based on a Net Exchange Rate formalism. The cold collar structure has been modeled when taking into account the latitudinal distribution of the cloud structure. Globally averaged profiles (e.g spatially and temporally) extracted from the state-of-the-art IPSL Venus GCM provide realistic templates of the atmosphere of Venus. <br>VEx observations revealed a more variable atmosphere than expected, in particular the “transition” region (~70-120 km) between the retrograde superrotating zonal flow and the day-to-night circulation showed latitude and day-to-day variations of temperature up to 80 K above 100 km at the terminator, and apparent zonal wind velocities measured around 96 km on the Venus nightime highly changing in space and time. Those variations are not fully explained by current 3D models and specific processes (e.g. gravity wave propagation, thermal tides, large scale planetary waves) responsible for driving them are still under investigation. The role of convectively-generated gravity waves and their impact on zonal wind and temperature in the region of aerobraking can be explored with the IPSL-VGCM, thanks to the inclusion of a stochastic non-orographic gravity waves parameterization, based on the Earth GCM. Data-model comparison of distribution of dynamical tracers above the clouds  (e.g O2(1Δ) nightglow, CO and O density) will be crucial to shed a light on a region where no direct wind measurements are available.<br>Akatsuki’s LIR camera revealed the presence of  planetary-scale mountain waves at the cloud top in the afternoon. Simulations of the upper atmosphere suggest that mountain waves can easily reach the upper atmosphere, to polar latitudes and the nightside, thus affecting atmospheric dynamics as high as 130 km.</p>