Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p21c0156b&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P21C-0156
Physics
5410 Composition (1060, 3672), 5419 Hydrology And Fluvial Processes, 5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Discovery of elevated sulfate and halite salts in sediments at the Mars Exploration Rover landing sites indicate that cemented surfaces may be common on Mars. This scenario is even more plausible if water is currently interacting with surface materials. Salt-cemented surfaces are a key indicator of the role water has and continues to play on the Martian surface. Additionally, water storage in hydrated salts in cements may account for the elevated water of hydration as suggested by Mariner data and hydrogen abundances reported by the Mars Odyssey team. Sulfate and halite cemented crusts have been synthesized in the lab with JSC-1, basalt, and quartz powders to measure the effect of cementation on thermal infrared spectra. In studying the effects of cementation, we found that cooled samples exhibited different emission spectra than those that were heated. When examined under SEM, heated gypsum crystal surfaces showed increased surface texture. In order to understand sample dehydration during preparation and by extension the emission spectra of the salt hydration states, we prepared individual hydrated sulfate samples for dehydration and analysis. Powdered samples of CaSO4-H2O and MgSO4-7H2O were pressed into pellets to reduce particle size scattering effects. Samples were heated at 80 degrees C for intervals of 2, 4, 8, 12 and 24 hours. At each interval, emission spectra were measured and the samples weighed. Although the weighing of the sample was meant to illustrate the amount of water lost, no quantitative analysis of water loss was performed as the relative humidity could not be maintained in our laboratory environment. The samples were sealed in containers in order to maintain the hydration state before XRD analysis. Results indicate that the thermal emission spectra change with heating of the sample. Effects were more subtle for MgSO4-nH2O than for CaSO4-nH2O. The effects are similar to particle size at short wavelengths although the intensity of the sulfate absorption increases with increased heating. XRD analyses confirm the transformation/dehydration of sulfate hydrates to less hydrated forms. The ability to identify hydrated salt mineralogy in cements will be important in determining the evolution and interaction of water with surface materials on Mars.
Baldridge Alice
Christensen Paul
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