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Rosetta-Alice observations of exospheric hydrogen and oxygen on Mars |
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| Authors: | Paul D Feldman Andrew J Steffl Michael F A’Hearn S Alan Stern David C Slater Henry B Throop Lori M Feaga |
| Institution: | a Johns Hopkins University, Department of Physics and Astronomy, 3400 N. Charles Street, Baltimore, MD 21218-2695, USA b Southwest Research Institute, Department of Space Studies, Suite 300, 1050 Walnut Street, Boulder, CO 80302-5150, USA c Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA d LATMOS, CNRS/UVSQ/IPSL, 11 Boulevard d’Alembert, 78280 Guyancourt, France e Johns Hopkins University Applied Physics Laboratory, Space Department, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA f Southwest Research Institute, P.O. Drawer 28510, San Antonio, TX 78228-0510, USA g Physics Department, Nebraska Wesleyan University, Lincoln, NE 68504-2794, USA |
| Abstract: | The European Space Agency’s Rosetta spacecraft, en route to a 2014 encounter with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on 25 February 2007, closest approach being at 01:54 UT. The Alice instrument on board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for in situ cometary spectroscopy in the 750-2000 Å spectral band, was used to study the daytime Mars upper atmosphere including emissions from exospheric hydrogen and oxygen. Offset pointing, obtained five hours before closest approach, enabled us to detect and map the H i Lyman-α and Lyman-β emissions from exospheric hydrogen out beyond 30,000 km from the planet’s center. These data are fit with a Chamberlain exospheric model from which we derive the hydrogen density at the 200 km exobase and the H escape flux. The results are comparable to those found from the Ultraviolet Spectrometer experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen emission at 1304 Å is detected at altitudes of 400-1000 km above the limb during limb scans shortly after closest approach. However, the derived oxygen scale height is not consistent with recent models of oxygen escape based on the production of suprathermal oxygen atoms by the dissociative recombination of  . |
| Keywords: | Mars Mars Atmosphere Atmospheres Evolution |
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