HR: 09:25h
AN: SH41C-06 INVITED     [Abstracts]
TI: Current View of the Venus-Solar Wind Interaction
AU: * Gunell, H
EM: herbert.gunell@physics.org
AF: Swedish Institute of Space Physics, Box 812, Kiruna, SE-98128 Sweden
AU: Barabash, S
EM: stas@irf.se
AF: Swedish Institute of Space Physics, Box 812, Kiruna, SE-98128 Sweden
AB: In this paper we endeavour to review the results on Venus-Solar Wind Interaction obtained in recent years and the current understanding of plasma processes at Venus. In the years after the Pioneer Venus Orbiter (PVO) the Cassini and Galileo spacecraft have flown by and made plasma measurements at Venus. Theoretical and numerical modelling have been used to study the interaction between Venus and the solar wind. The models that have been used include gas-dynamical, MHD, and quasi-neutral hybrid models. Several escape processes are at work at Venus: direct escape of pick-up ions, which yields escaper rates of 1×10²⁵s^-1 and 1.6×10²⁵s^-1 for H⁺and O⁺ respectively; sputtering of the atmosphere by incident pick-up ions is responsible for a oxygen atom loss rate of 6×10²⁴s^-1; detached plasma clouds, that were observed by PVO and may be the result of plasma instabilities have been estimate to contribute to a loss of 0.5-1×10²⁵s^-1; thermal escape and photo-chemical processes are expected to be negligible for oxygen, but for hydrogen the photo-chemical loss rate is 3.8×10²⁵s^-1. The numbers are quoted from Lammer et al. (Planetary and Space Science, in press, 2005). A wide variety of plasma waves are present at Venus. The waves can play an important role in the interaction between the solar wind and the ionosphere, and wave measurements can be used as a diagnostic tool for remote studies of plasma processes at the planet. Wave measurements at Venus have been interpreted as an indication of lightning, although this issue is still controversial. Energetic neutral atom (ENA) imaging is an emerging field that for Venus so far only has been studied through computer modelling. These numerical studies have predicted that the ENA flux at Venus is lower than that at Mars. Measurements by the Venus Express mission will shed more light on the physics behind the generation of ENAs. Venus has been observed in X-rays by the Chandra X-ray observatory. The observed X-rays can be explained by fluorescence of X-rays from the sun in Venus' atmosphere. X-rays from the solar wind charge exchange (SWCX) process have been found at Mars and are the dominating source of X-rays from comets. In agreement with the sensitivity of the observation no such X-rays were found at Venus, but SWCX X-rays may be revealed by future more sensitive observations.
UR: http://www.irf.se/~herbert
DE: 2154 Planetary bow shocks
DE: 2159 Plasma waves and turbulence
DE: 2164 Solar wind plasma
DE: 2194 Instruments and techniques
DE: 6295 Venus
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005