Photochemical controls on chlorine and bromine geochemistry at the Martian surface

Yu Yan Sara Zhao, Scott M. McLennan, W. Andrew Jackson, Suniti Karunatillake

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26 Scopus citations


Widely distributed perchlorate on the Martian surface and over three orders of magnitude variation in bromine abundances in surface samples are difficult to explain solely by chloride and bromide aqueous geochemistry. New experiments show that photochemical oxidation (ultraviolet wavelength 254 nm) of chloride- and bromide-bearing evaporative brines in the presence of silica beads produces substantial perchlorate (ClO−4), chlorate (ClO−3), and bromate (BrO−3) under conditions relevant to Mars. Neutral to alkaline aqueous environments result in the dominance of chlorate over perchlorate. Preferential atmospheric recycling of Br over Cl causes variable Br/Cl ratios, consistent with numerous in-situ measurements of Cl and Br abundances on Mars. Bromate reacts with organics more readily than chlorate or perchlorate, and its presence in subsurface brines could challenge habitability in the Martian subsurface.

Original languageEnglish
Pages (from-to)102-112
Number of pages11
JournalEarth and Planetary Science Letters
StatePublished - Sep 1 2018


  • Mars
  • bromate
  • halogen
  • perchlorate
  • photochemistry
  • sulfate


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