Effects of Formation Pathways and Bromide Incorporation on Jarosite Dissolution Rates: Implications for Mars

Abstract

AbstractThe dissolution rates of jarosite can constrain the duration of aqueous activities on Mars. To date, few studies have considered the influences of formation pathways and anion substitutions on jarosite dissolution rates. Here, we investigated how the formation pathways (Fe(II)‐oxidation and Fe(III)‐forced hydrolysis) and incorporation of bromide influence the dissolution rates of K‐jarosite under eight aqueous conditions combining T (277 K, 298 K, and 323 K) and αw (0.35, 0.75 and 1), except for 277 K−0.35αw. The results show that jarosite dissolution rates are primarily influenced by aqueous T‐αw conditions. Formation pathways and Br contents are secondary factors and only become notable under low T (277 K) and low αw (0.35) conditions. Taking the jarosite formation pathways and Br incorporation into account, the maximum lifetime of jarosite may be slightly longer than that of the halogen‐free counterparts formed via Fe(III)‐forced hydrolysis. Jarosite of the Burns Formation (Meridiani Planum) and the Pahrump Hills member (Gale Crater) are likely formed via Fe(II)‐oxidation and halogen‐bearing. Their estimated field lifetime (∼150 μm–1 mm particles) in low‐T groundwater may last for hundreds of thousand years to a few million years. Jarosite in the Vera Rubin Ridge would share a similar lifespan if low‐T solutions account for jarosite formation and subsequent interactions; otherwise, interactions with hydrothermal fluids (∼100°C) would substantially shorten the jarosite lifetime. We conclude that Martian jarosite may survive continuous aqueous interactions for up to a few million years, indicating an extended duration of aqueous environments than previously thought.