Séminaire LATMOS-OVSQ (Amphithéâtre Gérard Mégie, Guyancourt), Vendredi 22 novembre, 11h

Orateur: Vasili Kharchenko (Harvard-Smithsonian Center for Astrophysics, University of Connecticut)

Titre: Relaxation of Energetic Neutral Atoms and Escape from Planetary Atmospheres


Precipitation of Energetic Neutral Atoms (ENAs) produced  by  the solar wind and/or magnetospheric ions are investigated. Energy relaxation of ENAs are determined in Monte Carlo simulations of the precipitation process, taking into account  an accurate description of collisions between ENAs and atomic and molecular constituents of planetary atmospheres. Rates of the energy and momentum transfer in ENAs collisions with the atmospheric gas and production rates of secondary energetic atoms and molecules are evaluated with accurate cross sections obtained in ab initio quantum mechanical calculations and laboratory measurements. Collisions of precipitating particles with CO2 molecules, which are important constituents of the upper atmospheres of terrestrial planets, are described using  the semi-empirical quantum scaling procedure. For illustration, altitude profiles of the ion/ENAs energy deposition into the Mars atmosphere are calculated. The rates of  production of the secondary energetic (hot) atoms and molecules are determined. The escape fraction of fast atoms and molecules induced by precipitating ENAs are computed. Escape of molecular species from Mars' atmosphere is discussed in detail.