The role of sulfate minerals in the search for evidence of life on Mars

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Title: The role of sulfate minerals in the search for evidence of life on Mars
Authors: Lewis, James Michael Timothy
Item Type: Thesis or dissertation
Abstract: Spacecraft sent to Mars have revealed that some ancient martian environments were habitable for life. Attempting to detect the organic matter that this potential life may have left behind has been a priority for several missions. However, the search for both biotic and abiotic organic compounds on Mars has yielded only organochlorines, which have an ambiguous origin. Recently it has been recognised that perchlorate (ClO4-) salts found on the surface of Mars are interfering with the heating experiments used by rovers and landers to search for organic matter. The potential for other oxygen-containing salts to disrupt thermal experiments has received comparatively little attention. In this thesis it is shown that the iron sulfate mineral jarosite thermally decomposes and releases oxygen at temperatures that would interfere with the detection of macromolecular organic matter. Experiments using synthetic jarosite samples revealed that during thermal decomposition sulfur dioxide and oxygen are released concurrently at a ratio of 2:1. In the presence of organic matter only the sulfur dioxide is detected, along with the carbon dioxide resulting from the combustion of carbon compounds. Prolonged exposure to water eventually causes jarosite to decompose into goethite. It was found that goethite can retain organic matter that was originally preserved in jarosite. The results demonstrate that though jarosite should be considered a problematic mineral for thermal experiments on Mars, goethite deposits in close proximity to jarosite may be good targets for organic matter detection. Jarosite and goethite have been observed on Mars by both rovers and orbiters. The transition from a habitable world to the present environment was marked by volcanism that created jarosite-forming, acidic, sulfur-rich conditions. The improved knowledge of the thermal extraction of jarosite and goethite containing samples will therefore be relevant in the analysis of a significant part of Mars’ geological history.
Content Version: Open Access
Issue Date: Sep-2015
Date Awarded: Jan-2016
URI: http://hdl.handle.net/10044/1/48679
Supervisor: Sephton, Mark
Genge, Matthew
Sponsor/Funder: Science and Technology Facilities Council (Great Britain)
Department: Earth Science & Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Earth Science and Engineering PhD theses



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