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Evidence for perchlorates and the origin of chlorinated hydrocarbons detected by SAM at the Rocknest aeolian deposit in Gale Crater

Glavin, Daniel P. and Grotzinger, John P. (2013) Evidence for perchlorates and the origin of chlorinated hydrocarbons detected by SAM at the Rocknest aeolian deposit in Gale Crater. Journal of Geophysical Research. Planets, 118 (10). pp. 1955-1973. ISSN 2169-9097. doi:10.1002/jgre.20144.

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A single scoop of the Rocknest aeolian deposit was sieved (< 150 µm), and four separate sample portions, each with a mass of ~50 mg, were delivered to individual cups inside the Sample Analysis at Mars (SAM) instrument by the Mars Science Laboratory rover's sample acquisition system. The samples were analyzed separately by the SAM pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes. Several chlorinated hydrocarbons including chloromethane, dichloromethane, trichloromethane, a chloromethylpropene, and chlorobenzene were identified by SAM above background levels with abundances of ~0.01 to 2.3 nmol. The evolution of the chloromethanes observed during pyrolysis is coincident with the increase in O_2 released from the Rocknest sample and the decomposition of a product of N‐methyl‐N‐(tert‐butyldimethylsilyl)‐trifluoroacetamide (MTBSTFA), a chemical whose vapors were released from a derivatization cup inside SAM. The best candidate for the oxychlorine compounds in Rocknest is a hydrated calcium perchlorate (Ca(ClO_4)_2·nH_2O), based on the temperature release of O_2 that correlates with the release of the chlorinated hydrocarbons measured by SAM, although other chlorine‐bearing phases are being considered. Laboratory analog experiments suggest that the reaction of Martian chlorine from perchlorate decomposition with terrestrial organic carbon from MTBSTFA during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by SAM. Chlorobenzene may be attributed to reactions of Martian chlorine released during pyrolysis with terrestrial benzene or toluene derived from 2,6‐diphenylphenylene oxide (Tenax) on the SAM hydrocarbon trap. At this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons, nor do we exclude the possibility that future SAM analyses will reveal the presence of organic compounds native to the Martian regolith.

Item Type:Article
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Glavin, Daniel P.0000-0001-7779-7765
Grotzinger, John P.0000-0001-9324-1257
Additional Information:© 2013 American Geophysical Union. Received 13 May 2013; revised 23 July 2013; accepted 15 August 2013; published 1 October 2013. NASA provided support for the development of SAM. Data from these SAM experiments will be archived in the Planetary Data System ( in 2013. Essential contributions to the successful operation of SAM on Mars and the acquisition of these data were provided by the SAM development, operations, and testbed teams. D.P.G., J.L.E., K.E.M., M.G.M., J.P.D., and R.E.S. acknowledge funding support from the NASA ROSES MSL Participating Scientist Program. C.F. and P.D.A. acknowledge support from the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities through a contract with NASA. We thank M. Benna for providing input on the modeled pressure and flow conditions in SAM. We thank R. Quinn and an anonymous reviewer for helpful comments and appreciate valuable discussions with H. Steininger.
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:Mars Science Laboratory; Sample Analysis at Mars; Rocknest soil; chlorohydrocarbons; perchlorates; MTBSTFA
Issue or Number:10
Record Number:CaltechAUTHORS:20181127-133019547
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Official Citation:Glavin, D. P., et al. (2013), Evidence for perchlorates and the origin of chlorinated hydrocarbons detected by SAM at the Rocknest aeolian deposit in Gale Crater, J. Geophys. Res. Planets, 118, 1955–1973, doi: 10.1002/jgre.20144
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91231
Deposited By: Tony Diaz
Deposited On:27 Nov 2018 21:37
Last Modified:16 Nov 2021 03:39

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