Evaluation of Jarosite as a Biosignature: A Comparison of Biogenic and Synthetic Jarosites
Abstract
The detection of jarosite (K)Fe3(SO4)2OH6 on Mars has been interpreted as mineralogical evidence of acid-sulfate aqueous processes, including putative evidence of biological activity. Terrestrial habitats where acidic conditions occur are environments where microbiota thrive and generate biological signatures. A biotic and synthetic jarosite were produced to evaluate the ability and effectiveness of existing analytical methods to identify biosignatures in targeted geological materials. Using a comprehensive suite of microscopic (light microscopy, SEM and TEM), mineralogical (XRD), spectroscopic (IR, LIBS, Mössbauer, UV-Vis-NIR, and Raman) and mass spectrometry (ToF-SIMS) techniques, the two jarosites were found to be morphologically distinct. The identification of organic signatures in biogenic samples was masked by the iron-hydroxyl-sulfate matrix, but biogenicity was detectable using SEM and TEM which are not practical on Mars. Jarosite produced in 2-year-old abiotic control medium was similar to biogenic samples indicating that the presence of jarosite is not evidence of life.