^1,2Shuai-Yi Qu,^3,4Yu-Yan Sara Zhao,^5,6He Cui,⁶Shuai Zhang,⁷Xiuqin Yang,¹Honglei Lin,⁸Chao Qi,^4,9Xiongyao Li,^4,9Jianzhong Liu
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008688]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
²University of Chinese Academy of Sciences, Beijing, China
³Research Center for Planetary Science, College of Earth and Planetary Sciences, Chengdu University of Technology, Chengdu, China
⁴CAS Center for Excellence in Comparative Planetology, Hefei, China
⁵College of Life Sciences, Wuchang University of Technology, Wuhan, China
⁶Technical Center of Qingdao Customs, Qingdao, China
⁷State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry Chinese Academy of Sciences, Guiyang, China
⁸Center for High Pressure Science and Technology Advanced Research, Beijing, China
⁹Center for Lunar and Planetary Sciences, Institute of Geochemistry Chinese Academy of Sciences, Guiyang, China
Published by arrangement with John Wiley & Sons

Chlorine-bearing salts mixed with other minerals exposed to ultraviolet light participate in chlorine redox cycles on the Martian surface. Previous studies have shown that Fe^III sulfates can exclusively produce perchlorate by chloride photooxidation, but the mechanisms and effective scopes remain unclear. In this study, we investigated this perspective by conducting two main photochemical experiments using ultraviolet light 254 nm. Chloride oxidation experiments examined the effects of different Fe minerals (i.e., Fe^II sulfates, Fe^III sulfates, Fe^III chlorides, Fe^III nitrates, pyrrhotite, siderite and nontronite) and acidified non-Fe sulfates (Ca-, Mg-, Na-, and K- sulfates). Photocatalytic conversion experiments assessed the conversion products of perchlorate and chlorate in the presence of different sulfates (Fe^III, Ca, Mg, Na, and K). Our results showed that the ClO₃⁻/ClO₄⁻ molar ratios <<1 reported for Fe^III sulfates did not occur in any non-Fe sulfates, even after acidification by concentrated H₂SO₄. Other Fe salts, such as Fe^II sulfates, Fe^III nitrates, and Fe^III chlorides, also showed preferential ClO₄⁻ production, whereas pyrrhotite, siderite and nontronite produced more ClO₃⁻ than ClO₄⁻. Photocatalytic conversion experiments starting with NaClO₃ and NaClO₄ demonstrated that Fe^III can facilitate the direct NaClO₃-to-NaClO₄ conversion without producing Cl⁻ and inhibit the photolysis of NaClO₄. Our study highlights the unique role of hygroscopic Fe salts (both Fe^II and Fe^III) in the production and preservation of perchlorate. Mineral surfaces and water vapor may play essential roles in the chlorine redox cycle. The likely coexistence of perchlorate and Fe^III salts has important implications for liquid water on the present cold and arid Mars.

¹Atsushi Takenouchi,²Hirochika Sumino,^3,4Hideyuki Hayashi,⁵Takashi Mikouchi,⁶Martin Bizzarro
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70055]
¹Kyoto University Museum, Kyoto University, Kyoto, Japan
²Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁴National Museum of Nature and Science, Ibaraki, Japan
⁵The University Museum, The University of Tokyo, Tokyo, Japan
⁶Center for Star and Planet Formation, University of Copenhagen, Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

Angrites and eucrites are among the oldest basaltic rocks in the solar system. However, the shock histories of these meteorite groups differ markedly, as most angrites show little to no evidence of shock metamorphism. While some angrites exhibit weak wavy extinction in olivine, indicative of low-level shock, only two—Northwest Africa (NWA) 1670 and NWA 7203—are known to preserve significant shock features such as shock melt veins. To better constrain the shock history of angrites, we performed noble gas analyses on the rare shock-metamorphosed angrite NWA 7203 to determine its cosmic ray exposure and gas retention ages. Neon in NWA 7203 is entirely cosmogenic, and combined neon and argon data yield a cosmic ray exposure age of 22.7 ± 3.1 Ma (2σ). This age nominally differs from that of the other shocked angrite, NWA 1670, but is comparable to that of the unshocked angrite NWA 7812. NWA 7203 may have been ejected from a rubble pile-like asteroid composed of both shocked and unshocked materials. Two distinct 40Ar/39Ar apparent ages, 3.38 ± 0.10 Ga and 1.41 ± 0.11 Ga, were obtained, likely reflecting variable argon loss during a single impact-induced thermal event that occurred no earlier than 1.41 ± 0.11 Ga (2σ). This is the first report for the shock metamorphic age of an angrite. Our results reinforce the view that even shocked angrites lack clear evidence of a catastrophic disruption of their parent body (>100 km) hypothesized to have occurred in the early solar system. To resolve this conundrum, we propose that angrites may have experienced extensive melting during such an event, which suppressed or erased conventional shock features. If this impact occurred near the time of their crystallization (>4564 Ma), it may have been a “hot shock” event driven by heat from short-lived radionuclides. Such an event could have generated large volumes of shock melt, from which quenched angrites subsequently formed. We suggest that differentiated planetary bodies may have commonly undergone such early-stage disruption events during the formative epoch of the solar system.