P21A-2049
Precipitating Solar Wind Hydrogen at Mars
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Jasper S Halekas1, Robert J Lillis2, David L Mitchell2, Christian Xavier Mazelle3, John E P Connerney4, Jared R Espley4, Mehdi Benna4, James P McFadden2, Janet G Luhmann2, Bruce Martin Jakosky5 and Paul R Mahaffy4, (1)University of Iowa, Physics and Astronomy, Iowa City, IA, United States, (2)University of California Berkeley, Berkeley, CA, United States, (3)University Paul Sabatier Toulouse III, Toulouse Cedex 09, France, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
Abstract:
MAVEN has observed precipitating solar wind hydrogen deep in the atmosphere of Mars. Solar wind protons charge exchange with neutral particles in the extended Martian corona, forming a stream of energetic neutral atoms which penetrate through the magnetosphere unaffected by electromagnetic fields, still retaining the solar wind velocity. The resulting hydrogen beam interacts with the dense neutral atmosphere at low altitudes, producing three different charge states (H+, H, H-), the ratio of which depends upon the energy-dependent collision cross sections with neutral species (dominantly CO2 at low altitudes). We first discuss the utility of the penetrating proton population as a solar wind proxy, demonstrating the systematic organization of magnetospheric structure and escaping fluxes by the penetrating proton measurements. We then compare H+ and H- fluxes at periapsis to the upstream solar wind flux, as a function of solar wind energy and atmospheric density, to constrain the energy dependence of the relevant electron stripping, electron attachment, and charge exchange cross sections. Next, we investigate the spatial and temporal organization of the penetrating fluxes observed during the MAVEN mission, which allow us to determine both the effects of crustal magnetic fields and the seasonal variability of the Martian corona. Finally, we discuss the relevance of observed hydrogen deposition for the short-term and long-term evolution of the Martian atmosphere and magnetosphere.
