Physics
Scientific paper
Apr 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgre..11404010w&link_type=abstract
Journal of Geophysical Research, Volume 114, Issue E4, CiteID E04010
Physics
7
Planetary Sciences: Solar System Objects: Mars, Mineralogy And Petrology: Experimental Mineralogy And Petrology, Mineral Physics: Optical, Infrared, And Raman Spectroscopy
Scientific paper
Dehydration/rehydration experiments were conducted on pure Mg-sulfates and mixtures of epsomite with Ca-sulfates, Fe-sulfates, Fe-oxide, and Fe-hydroxide. The goal was to investigate the stabilities and phase transition pathways of Mg-sulfate hydrates, under temperature and relative humidity conditions relevant to Mars, as a function of starting structure and coexisting species. Two pathways were found to form Mg-sulfate monohydrates between 5°C and 50°C through dehydration of epsomite or hexahydrite. Two polymorphs of Mg-sulfate monohydrates were characterized in this study. It is important to distinguish among these phases on Mars because they have different formation conditions that have the potential to provide additional information on surface and subsurface geologic processes. We found that Mg-sulfates with moderate hydration states (especially starkeyite and amorphous Mg-sulfates) can be very stable under current Martian surface conditions. On the basis of NIR spectral features, these phases are good candidates for polyhydrated sulfates identified on Mars by OMEGA and CRISM; thus, they may contribute to the high hydrogen concentrations found by the neutron spectrometer on the orbiting Odyssey spacecraft. Our experiments indicate that the maximum number of water molecules per SO4 held by the amorphous Mg-sulfate structure is three. In addition, the amorphization rate of Mg-sulfates is strongly dependent on temperature. The low temperature (approximately -80°C) in the early morning hours during the Martian diurnal cycle would slow the dehydration rate, which would favor the stability of starkeyite over amorphous Mg-sulfates and would lead to a low abundance of the latter.
Freeman John J.
Jolliff Bradley L.
Wang Alian
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