Composition and Chemistry of the Neutral Atmosphere of Venus

Abstract

International audienceThis paper deals with the composition and chemical processes occurring in the neutral atmosphere of Venus. Since the last synthesis, observers as well as modellers have emphasised the spatial and temporal variability of minor species, going beyond a static and uniform picture that may have prevailed in the past. The outline of this paper acknowledges this situation and follows closely the different dimensions along which variability in composition can be observed: vertical, latitudinal, longitudinal, temporal. The strong differences between the atmosphere below and above the cloud layers also dictate the structure of this paper. Observational constraints, obtained from both Earth and Venus Express, as well as 1D, 2D and 3D models results obtained since 1997 are also extensively referred and commented by the authors. An non-exhaustive list of topics included follows: modelled and observed latitudinal and vertical profiles of CO and OCS below the clouds of Venus; vertical profiles of CO and SO2 above the clouds as observed by solar occultation and modelled; temporal and spatial variability of sulphur oxides above the clouds. As a conclusion, open questions and topics of interest for further studies are discussed

Venus Atmospheric Thermal Structure and Radiative Balance

“…Below we present the status of our knowledge of the Venus atmospheric thermal structure and radiative balance that incorporates recent observations. We note that recent results on the atmospheric circulation are discussed in depth recently by , the atmospheric chemistry by Marcq et al (2018), while the cloud structure results are summarized by Titov et al (2018). In this paper, we present an overview of the thermal structure observations (Sect.…”

“…It is characterized by a hot dayside and a very cold nightside, separated by a sharp and key transition region, the terminator. Kasprzak et al (1997) have previously discussed the neutral composition, thermal structure, dynamics and effects of the solar activity and Marcq et al (2018) present an update on the composition and chemistry of the neutral atmosphere. Since then, the SOIR infrared Nevejans et al 2006) and SPICAV-UV (Bertaux et al 2007a(Bertaux et al , 2007b spectrometers, the aerobraking experiment VEXADE (Müller-Wodarg et al 2006) and the torque experiment (Persson 2015;Rosenblatt et al 2012) of the Venus Express mission focused on studying the composition, mass density and temperature structure of the thermosphere.…”

“…Thus understanding the thermal structure requires a knowledge of the absorption of the incident solar radiation and escape to space of the emitted infrared radiation from the surface and the atmosphere itself. Both the absorption and escape of radiation depend on the cloud structure and the chemical composition of the atmosphere, which have been reviewed in the companion papers by Titov et al (2018) and Marcq et al (2018) respectively.…”

Geoscience for Understanding Habitability in the Solar System and Beyond

“…Non-thermal escape is thought to have had a significant effect on the long-term evolution of terrestrial planets, contributing to the shift from a wet early Mars to dry present-day conditions as evidenced by the D/H ratio in the Martian atmosphere (Carr, 1990). The same scenario has been discussed for Venus (Donahue, 1999) but here the situation is more complex (Grinspoon, 1993; because of large variations of D/H ratio with altitude (Marcq et al, 2018).…”

Millimeter‐Wave Radiometric Information Content Analysis for Venus Atmospheric Constituents

“…In addition to the above, water is also present on Venus as vapor in the atmosphere and the content does not exceed 100 ppm at any altitude and is bound with sulfuric acid in the cloud droplets. However, the total water abundance is significantly small in comparison to carbon dioxide and nitrogen (Marcq et al, ).…”