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 (ClO 4 – ). 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 (HClO 4 ) in the atmosphere, and the surface deposition and subsequent mineralization of HClO 4 in 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 × 10 7 molecules cm –2 s –1 sublimated into the atmosphere from the surface could produce sufficient HClO 4 to 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 HClO 4 formation mechanisms proposed for the Earth but not Mars.

Evolved gas analyses of sedimentary rocks and eolian sediment in Gale Crater, Mars: Results of the Curiosity rover's sample analysis at Mars instrument from Yellowknife Bay to the Namib Dune

“…Postdepositional solutions enriched or depleted in soluble salts could raise or lower the soluble salt contents, respectively, of the Gale materials. Other post depositional oxidizing or reducing processes could also affect the oxychlorine contents [e.g., Catling et al ., ; Quinn et al ., ; Wilson et al ., ]. More detailed analysis of the mineralogy and geochemistry coupled with laboratory analysis will be required to understand the nature and origins of the oxychlorine distribution in Gale Crater.…”

Chlorate/Fe‐Bearing Phase Mixtures as a Possible Source of Oxygen and Chlorine Detected by the Sample Analysis at Mars Instrument in Gale Crater, Mars

“…Chlorate is detected in comparable abundances to perchlorate on Earth (Rao et al, ), so it is likely an important part of the chlorine cycle on Mars as well. Perchlorate on Mars has been proposed to form by the oxidation of chloride by semiconducting oxide minerals (Schuttlefield et al, ), the radiolysis of Martian surface materials by galactic cosmic rays (Wilson et al, ), and/or photochemical oxidation of chlorine‐bearing minerals (Carrier & Kounaves, ). Like perchlorate, chlorate has been suggested to be an end product of chloride or oxychlorine oxidation (Dasgupta et al, ; Kang et al, ).…”

Degradation of Adenine on the Martian Surface in the Presence of Perchlorates and Ionizing Radiation: A Reflectron Time-of-flight Mass Spectrometric Study

“…Perchlorates -( ) ClO 4 are considered to be the most effective oxidants (Hecht et al 2009;Glavin et al 2013), with concentrations that can be as high as 1.0% by weight (Davila et al 2013). They are likely formed via heterogeneous photochemical (Smith et al 2014), photocatalytic (Carrier & Kounaves 2015), or radiation-induced surface reactions within carbon dioxide (CO 2 )-bearing ices (Kim et al 2013;Wilson et al 2016).…”