Aeronomy of the Venus Upper Atmosphere

Abstract

We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus' upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O 2 nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons.

Solar Wind Interaction and Impact on the Venus Atmosphere

“…On the other hand, the hybrid models bring out asymmetries in the interaction caused by the fact that the unmagnetized obstacle of Venus has a comparable scale to the major (O + , O 2 + , CO 2 + ) planetary ion species involved in that interaction. Both of these models complement the work on atmosphere/ionosphere models described in the accompanying article by Gérard et al (2017). However, up to now there has been no specific attempt to merge the models in these different, though overlapping, domains.…”

“…In particular, the merging of the state of the art upper atmosphere and ionospheric chemistry models (see Gérard et al 2017 in this volume) with the solar wind interaction models can be used to investigate such questions as the role of neutral winds on the solar wind interaction and the consequences of the heavy pickup ion precipitation (e.g. sputtering-see Luhmann and Kozyra 1991).…”

Future of Venus Research and Exploration

“…In addition to dedicated missions, observations by fly-by spacecraft equipped with plasma and field instrumentation can also provide valuable new data (Coradini et al 2015). Finally, sustained time-series observations of near-infrared molecular emissions in the mesosphere would increase understanding of observed spectral and spatial variability in airglow on the night side (Gerard et al 2017, this issue).…”

Radio Occultation on the Venera-D Mission: A Concept of Radio Frequency Subsystem and Radio Science Technique

“…Radio-obscuration studies on Venus began in 1967 [2]. Thanks to the successful missions of the spacecraft (SC) MARINER-5,-10, VENUS-9,-10, PIONEER-VENUS, VENUS-15,-16, MAGELLAN, VENUS-EXPRESS, AKATSUKI, more than 1500 radio transmissions of the Venosphere and Venus atmosphere were conducted [3][4][5][6][7][8][9]. The amount of radio sounding data accumulated to date is relatively small (~1500 sessions), while the amount of radio sounding of the Martian gas envelope exceeds 6000, the number of radio sounding of the near-earth shell is several thousand per day and several million sessions have been conducted.…”

“…Using the available experimental data, the structural characteristics of the ionosphere and the upper atmosphere of Venus were investigated and described in the literature [1][2][3][4][5][6][7][8][9]. These results cover a wide range of altitudes above the surface of the planet and solar activity.…”