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Reevaluation of Perchlorate in Gale Crater Rocks Suggests Geologically Recent Perchlorate Addition

Martin, Peter E. and Farley, Kenneth A. and Archer, P. Douglas Jr. and Hogancamp, Joanna V. and Siebach, Kirsten L. and Grotzinger, John P. and McLennan, Scott M. (2020) Reevaluation of Perchlorate in Gale Crater Rocks Suggests Geologically Recent Perchlorate Addition. Journal of Geophysical Research. Planets, 125 (2). Art. No. e2019JE006156. ISSN 2169-9097.

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Perchlorate (ClO₄⁻) was discovered in Martian soil by the Phoenix lander, with important implications for potential Martian biology, photochemistry, aqueous chemistry, and the chlorine cycle on Mars. Perchlorate was subsequently reported in both loose sediment and bedrock samples analyzed by the Sample Analysis at Mars instrument onboard the Curiosity rover in Gale crater based on a release of O₂ at 200–500°C. However, the continually wet paleoenvironment recorded by the sedimentary rocks in Gale crater was not conducive to the deposition of highly soluble salts. Furthermore, the preservation of ancient perchlorate to the modern day is unexpected due to its low thermodynamic stability and radiolytic decomposition associated with its long exposure to radioactivity and cosmic radiation. We therefore investigate alternative sources of O₂ in Sample Analysis at Mars analyses including superoxides, sulfates, nitrate, and nanophase iron and manganese oxides. Geochemical evidence and oxygen release patterns observed by Curiosity are inconsistent with each of these alternatives. We conclude that perchlorate is indeed the most likely source of the detected O2 release at 200–500°C, but contend that it is unlikely to be ancient. Rather than being associated with the lacustrine or early diagenetic environment, the most likely origin of perchlorate in the bedrock is late stage addition by downward percolation of water through rock pore space during transient wetting events in the Amazonian. The conclusion that the observed perchlorate in Gale crater is most likely Amazonian suggests the presence of recent liquid water at the modern surface.

Item Type:Article
Related URLs:
URLURL TypeDescription
Martin, Peter E.0000-0003-4243-2090
Farley, Kenneth A.0000-0002-7846-7546
Hogancamp, Joanna V.0000-0003-2556-8586
Siebach, Kirsten L.0000-0002-6628-6297
Grotzinger, John P.0000-0001-9324-1257
McLennan, Scott M.0000-0003-4259-7178
Additional Information:© 2020 American Geophysical Union. Received 7 AUG 2019; Accepted 16 JAN 2020; Accepted article online 30 JAN 2020. We thank Brad Sutter for many thoughtful and spirited debates which improved this manuscript. We also thank the SAM and Curiosity teams for their support in rover operations, without which this work would not be possible. SAM data are available on the Planetary Data System (PDS; pds‐ Additional data used in this study are available on the CaltechDATA repository at Funding was provided by NASA.
Funding AgencyGrant Number
Subject Keywords:Mars; perchlorate; chlorine; evolved gas analysis; Curiosity; Sample Analysis at Mars
Issue or Number:2
Record Number:CaltechAUTHORS:20200302-130340431
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Official Citation:Martin, P. E., Farley, K. A., Douglas, P., Hogancamp, J. V., Siebach, K. L., Grotzinger, J. P., & McLennan, S. M. (2020). Reevaluation of perchlorate in Gale crater rocks suggests geologically recent perchlorate addition. Journal of Geophysical Research: Planets, 125, e2019JE006156.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101652
Deposited By: Tony Diaz
Deposited On:02 Mar 2020 21:11
Last Modified:03 Aug 2020 19:07

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