Seasonal and Dust Storm Variability in Mars H Escape inferred from MAVEN/IUVS Lyman Alpha Brightness Measurements

Over time, a large fraction of Martian water has been lost to space. The H component of this loss is expected to be mostly thermal, and has been shown to vary by more than an order of magnitude from Northern Summer (near aphelion) to Southern Summer (near perihelion). The mechanism responsible for this increase is expected to be lofting of water to high altitudes by the more turbulent Southern Summer atmosphere, where it can more readily dissociate and provide H to the upper atmospheric escape region. Dust activity and global dust storms are expected to increase turbulence in the lower atmosphere and increase atmospheric temperatures significantly, potentially allowing even more water to access high altitudes. The MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft has been present at Mars for two Mars years, providing its Imaging Ultraviolet Spectrograph (IUVS) with the opportunity to observe upper atmospheric variability over multiple Southern Summers. Most recently, the occurrence of a large global dust storm in mid-2018 provides the opportunity to contrast the seasonal and dust-induced behavior of upper atmospheric H and H escape. We will present MAVEN/IUVS observations and retrievals over multiple Mars years, including the dust storm year, to quantify the impact of dust storms on atmospheric escape.