MAVEN IUVS and HST Observations of the Martian Exosphere During the 2018 Dust Storm

Abstract : Over the past decade a repeated pattern of increased hydrogen abundance and escape flux has been observed centered near southern summer solstice (solar longitude L_S 270). Explanations have invoked the upwelling of water into the middle atmosphere to supply the increased H and D atoms to the upper atmosphere, connected with lower atmospheric turbulence and likely enhanced by dust. The global dust storm at Mars in June/July 2018 occurred around L_S 180-220, well before the known H maximum, giving the opportunity to separately measure the contribution of dust from seasonal changes. Observations of H Lyman-alpha emissions from the upper atmosphere of Mars have been made with the MAVEN IUVS instrument and at two epochs with HST to determine the time scale for changes in H and D abundances and escape rates. The observations are ongoing at the time of abstract submission, and the results will be presented along with any conclusions about the contribution of different processes to the annual cycle in H and D escape rates.