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

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 3 hr 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 120 km, consistent with comet Siding Spring's relative velocity of 56 km/s. We find that 82 ± 25 t 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.