HR: 16:15h
AN: SH54A-02 INVITED     [Abstracts]
TI: Exploring the Moon and Mars solar wind interaction using energetic neutral atoms
AU: * Holmstrom, M
EM: matsh@irf.se
AF: Swedish Institute of Space Physics, PO Box 812, Kiruna, SE-981 28 Sweden
AU: Barabash, S
EM: stas@irf.se
AF: Swedish Institute of Space Physics, PO Box 812, Kiruna, SE-981 28 Sweden
AB: The Moon and Mars are non-magnetized bodies. Therefore the solar wind can interact directly with the surface of the Moon and the upper parts of Mars' atmosphere. This is in contrast to the situation at magnetized planets, where the planet is protected by a magnetosphere. The solar wind interaction can be remotely studied by energetic neutral atom (ENA) imaging. Here we consider the energy regime 10 eV-10 keV, and review the different sources of ENAs at the Moon and at Mars. At the Moon, ENAs are produced by sputtering resulting from the precipitating solar wind. These sputtered neutrals can be imaged by an orbiting ENA detector. These images can produce information on space weathering, magnetic anomalies, and surface composition. At Mars, hydrogen ENAs are produced by charge exchange between solar wind protons and neutrals in Mars' exosphere. Imaging of these ENAs provide global information on the distributions of ions and neutrals. It is however not straight forward to extract this information from an ENA image, since we only know the ENA flux integrated along lines of sight. Inverse modeling is needed to extract parameters from observed ENA images. Another production mechanism for ENAs is that when solar wind protons and hydrogen ENAs precipitate onto the upper parts of Mars' atmosphere, they produce an outflux of ENAs by sputtering and backscattering, respectively. Also, a source of oxygen ENAs is from photoionized oxygen that is accelerated, and then charge exchange with neutrals. Another possible source of ENAs at Mars is from solar wind charge exchange with the Phobos gas torus. For Mars we also review the effects on the different ENA populations of using hybrid or MHD models for computer simulations of the ENA production. Observations of the above mentioned ENA populations at Mars can, with the help of modeling, provide, e.g., estimates of oxygen escape and carbon dioxide sputtered by oxygen ions.
DE: 7837 Neutral particles
DE: 7843 Numerical simulation studies
DE: 2151 Neutral particles
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting