Perchlorate Formation by Radiolysis on Mars

With recent observations indicating the presence of perchlorate (ClO4-) in the Martian surface by the Phoenix lander and the Sample Analysis at Mars (SAM) on the Mars Science Laboratory (MSL) rover, we employ a one-dimensional chemical model to investigate the viability of perchlorate formation in the atmosphere of Mars, instigated by the radiolysis of the Martian surface by galactic cosmic rays. The surface-atmosphere interaction to produce Martian perchlorate involves the injection of chlorine oxides into the atmosphere through surface radiolysis and the subsequent chemical conversion to perchloric acid (HClO4), followed by surface deposition and mineralization to perchlorate. Considering the chlorine oxide, OClO, we find an effective mechanism for forming perchloric acid, bypassing the efficient Cl/HCl recycling mechanism that characterizes HClO4 formation mechanisms proposed for the Earth. Through this mechanism, an OClO surface flux as low as 3.2*107 molecules cm-2 s-1 could produce enough HClO4 to explain the perchlorate concentration observed on Mars. These results could have wide-ranging implications in our understanding of chlorine chemistry on both Earth and Mars.