Metallic ions in the upper atmosphere of Mars from the passage of comet C/2013 A1 (Siding Spring)

We report the first in situ detection of metal ions in the upper atmosphere of Mars resulting from the ablation of dust particles from comet Siding Spring. This detection was carried out by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution Mission. Metal ions of Na, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and possibly of Si, and Ca, were identified in the ion spectra collected at altitudes of ∼185 km. The measurements revealed that Na⁺ was the most abundant species, and that the remaining metals were depleted with respect to the CI (type 1 carbonaceous Chondrites) abundance of Na⁺. The temporal profile and abundance ratios of these metal ions suggest that the combined effects of dust composition, partial ablation, differential upward transport, and differences in the rates of formation and removal of these metal ions are responsible for the observed depletion.