Abstract
Recent findings by the Mars Science Laboratory (MSL) have confirmed the
presence of nitrates near Gale Crater on Mars. In this work, we consider
the formation and deposition of HNOx species in cold early Mars
climates. We find that solar energetic particles could facilitate
nitrogen fixation by photochemically generating pernitric and nitric
acid, which then deposit onto icy particles that settle onto Mars’
surface. This study demonstrates that such deposition would be more
efficient under higher atmospheric pressures, consistent with Mars’
ancient atmosphere, and could account for the nitrate levels detected by
the MSL. We find a more rapid deposition rate for pernitric acid over
nitric acid (in agreement with Smith et al., 2014), and a significant
enhancement of deposition rates through consideration of deposition onto
icy particles. This distinction could be crucial for interpreting the
MSL data.