title: Perchlorate formation on Mars through surface radiolysis-initiated atmospheric chemistry: A potential mechanism.
abstract: Recent observations of the Martian surface by the Phoenix lander and the Sample Analysis at Mars indicate the presence of perchlorate (ClO4-). The abundance and isotopic composition of these perchlorates suggest that the mechanisms responsible for their formation in the Martian environment may be unique in our solar system. With this in mind, we propose a potential mechanism for the production of Martian perchlorate: the radiolysis of the Martian surface by galactic cosmic rays, followed by the sublimation of chlorine oxides into the atmosphere and their subsequent synthesis to form perchloric acid (HClO4) in the atmosphere, and the surface deposition and subsequent mineralization of HClO4in the regolith to form surface perchlorates. To evaluate the viability of this mechanism, we employ a one-dimensional chemical model, examining chlorine chemistry in the context of Martian atmospheric chemistry. Considering the chlorine oxide, OClO, we find that an OClO flux as low as 3.2 × 107molecules cm-2s-1sublimated into the atmosphere from the surface could produce sufficient HClO4to explain the perchlorate concentration on Mars, assuming an accumulation depth of 30 cm and integrated over the Amazonian period. Radiolysis provides an efficient pathway for the oxidation of chlorine, bypassing the efficient Cl/HCl recycling mechanism that characterizes HClO4formation mechanisms proposed for the Earth but not Mars.
authors: Department of Climate and Space Sciences and Engineering University of Michigan Ann Arbor Michigan USA.
authors: Eric H
authors: EH
authors: Wilson
authors: Department of Climate and Space Sciences and Engineering University of Michigan Ann Arbor Michigan USA.
authors: Sushil K
authors: SK
authors: Atreya
authors: Department of Chemistry University of Hawai'i at Mānoa Honolulu Hawaii USA.
authors: Ralf I
authors: RI
authors: Kaiser
authors: NASA Goddard Space Flight Center Greenbelt Maryland USA.
authors: Paul R
authors: PR
authors: Mahaffy
keywords: Mars; chlorine chemistry; radiolysis; surface‐atmosphere interactions