P12A-06
Oxygen Pickup Ions Measured by MAVEN Outside the Martian Bow Shock
Monday, 14 December 2015: 11:35
3002 (Moscone West)
Ali Rahmati1, Thomas Cravens1, Davin E Larson2, Robert J Lillis2, P Dunn3, Jasper S Halekas4, John E P Connerney5, Francis Gerard Eparvier6, Edward Thiemann7, David L Mitchell3, Bruce Martin Jakosky7 and The MAVEN Team, (1)University of Kansas, Lawrence, KS, United States, (2)University of California Berkeley, Berkeley, CA, United States, (3)Space Sciences Laboratory, Berkeley, CA, United States, (4)University of Iowa, Physics and Astronomy, Iowa City, IA, United States, (5)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (6)University of Colorado at Boulder, Boulder, CO, United States, (7)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
Abstract:
The MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft entered orbit around Mars on September 21, 2014 and has since been detecting energetic oxygen pickup ions by its SEP (Solar Energetic Particles) and SWIA (Solar Wind Ion Analyzer) instruments. The oxygen pickup ions detected outside the Martian bowshock and in the upstream solar wind are associated with the extended hot oxygen exosphere of Mars, which is created mainly by the dissociative recombination of molecular oxygen ions with electrons in the ionosphere. We use analytic solutions to the equations of motion of pickup ions moving in the undisturbed upstream solar wind magnetic and motional electric fields and calculate the flux of oxygen pickup ions at the location of MAVEN. Our model calculates the ionization rate of oxygen atoms in the exosphere based on the hot oxygen densities predicted by Rahmati et al. (2014), and the sources of ionization include photo-ionization, charge exchange, and electron impact ionization. The photo-ionization frequency is calculated using the FISM (Flare Irradiance Spectral Model) solar flux model, based on MAVEN EUVM (Extreme Ultra-Violet Monitor) measurements. The frequency of charge exchange between a solar wind proton and an oxygen atom is calculated using MAVEN SWIA solar wind proton flux measurements, and the electron impact ionization frequency is calculated based on MAVEN SWEA (Solar Wind Electron Analyzer) solar wind electron flux measurements. The solar wind magnetic field used in the model is from the measurements taken by MAVEN MAG (magnetometer) in the upstream solar wind. The good agreement between our predicted pickup oxygen fluxes and the MAVEN SEP and SWIA measured ones confirms detection of oxygen pickup ions and these model-data comparisons can be used to constrain models of hot oxygen densities and photochemical escape flux.
