^1,3Anna Neubeck, ²Marek Tulej, ³Magnus Ivarsson, ¹Curt Bromana, ²Andreas Riedo, ⁴Sean McMahon, ²Peter Wurz, ³Stefan Bengtson
¹Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden
²Space Research and Planetary Sciences, Physics Institute, University of Bern, CH-3012 Bern, Switzerland
³Department of Palaeobiology and Nordic Center for Earth Evolution (NordCEE), Swedish Museum of Natural History, Stockholm, Sweden
⁴Department of Geology & Geophysics, Yale University, Connecticut, USA

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Reference
Neubeck A, Tulej M, Ivarsson M, Broman C, Riedo A, McMahon S, Wurz P, Bengtson S (2015) Mineralogical determination in situ of a highly heterogeneous material using a miniaturized laser ablation mass spectrometer with high spatial resolution. International Journal of Astrobiology (in Press)
Link to Article [DOI: http://dx.doi.org/10.1017/S1473550415000269]

¹Alian Wang,¹Bradley L. Jolliff,²Yang Liu,¹Kathryn Connor
¹Dept. Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University in St. Louis, USA
²Southwest Research Institute, San Antonio, Texas, USA

Monohydrated Mg sulfate (MgSO4·H2O) and polyhydrated sulfate are the most common and abundant hydrous sulfates observed thus far on Mars. They are widely distributed and coexist in many locations. On the basis of results from two new sets of experiments, in combination with past experimental studies and the subsurface salt mineralogy observed at a saline playa (Dalangtan, DLT) in a terrestrial analogue hyperarid region on the Tibet Plateau, we can now set new constraints on the nature and origin of these two major martian sulfates. Starkeyite (MgSO4·4H2O) is the best candidate for polyhydrated sulfate. MgSO4·H2O in the form of “LH-1w” [Wang et al., 2009], generated from dehydration of Mg-sulfates with high degrees of hydration, is the most likely mineral form for the majority of martian monohydrated Mg-sulfate. Two critical properties of Mg-sulfates are responsible for the coexistence of these two phases that have very different degrees of hydration: (1) the metastability of a sub-structural unit in starkeyite at relatively low temperatures; and (2) catalytic effects attributed to co-precipitated species (sulfates, chlorides, oxides, and hydroxides) from chemically complex brines that help overcome the metastability of starkeyite. The combination of these two properties controls the coexistence of the LH-1w layer and starkeyite layers at many locations on Mars, which sometimes occur in an interbedded stratigraphy. The structural H2O held by these two broadly distributed sulfates represents a large H2O reservoir at the surface and in the shallow subsurface on current Mars.

Reference
Wang A, Jolliff BL, Liu Y, Connor K (2016) Setting Constraints on the Nature and Origin of the two Major Hydrous Sulfates on Mars — Monohydrated and Polyhydrated Sulfates. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004889]
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