The Impact of Comet Siding Spring's Meteors on the Martian Atmosphere and Ionosphere

Plain Language Summary On 19 October 2014, comet C/2013 A1 (Siding Spring) had a close encounter with Mars and deposited cometary dust particles into the Martian atmosphere. We report a comprehensive analysis of the resulting meteor shower and its perturbation on Mars' atmosphere and ionosphere. Using Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph observations of ablated meteoric metallic species, we show this shower lasted less than 3hr and was therefore limited to one hemisphere. Meteoric ablation occurred in a narrow altitude layer, with Mg+, Mg, Fe+, and Fe deposited between about 105 and 120km, consistent with comet Siding Spring's relative velocity of 56km/s. We find that 8225t of dust was deposited, improving previous measurements and a thousand times larger than model expectations. With regular observations over two Mars days, we show that horizontal winds globally redistribute this material and also suggest new vertical transport mechanisms for metallic ions. Such transport is inconsistent with diffusion and may be related to electrodynamic processes. The rapid loss of neutral species and presence of ions at high altitudes indicate that our understanding of existing Martian meteoric chemistry modeling and ionospheric dynamics is incomplete. A close encounter of Mars with Comet Siding Spring resulted in the largest meteor shower in modern history, depositing orders of magnitudes more dust than a typical meteor shower. This unique event creates the opportunity to observe metallic species not normally observed, and their resulting chemistry and dynamics. This work constrains the duration of the meteor shower and revises the deposited cometary dust mass to 82,000kg, more than the initial study and in excess of model expectations.