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Telling a salty tale of martian water

DOE/Los Alamos National Laboratory : 27 May, 2007  (Technical Article)
University of California scientists working at Los Alamos National Laboratory, along with a scientist from Indiana University have devised a method for determining whether sulfate salts can account for evidence of water on Mars. The work could pave the way to a better understanding of the martian environment and the history of water on Mars.
In a paper published in today's issue of the scientific journal Nature, a team of researchers lead by Los Alamos scientist David Vaniman describe the exposure of magnesium sulfate salts to various temperature, pressure and humidity conditions in order to understand their possible hydration states under martian surface conditions. The researchers discovered that the crystalline structure and water content of the salts are dependent on time-humidity history and that magnesium sulfate salts could retain sufficient water to explain at least a portion of the NASA Odyssey observations, which revealed surprisingly high abundances of near-surface hydrogen.

According to Vaniman, 'It's important to recognize that despite several unmanned missions to explore the geology of Mars, we still know relatively little about the martian environment and especially the history of water on Mars. This work is characteristic of the kind of knowledge base we need to create before humans ever travel to Mars, so that we can understand the martian world once we get there.'

The experiments examined the formation and transformation of magnesium sulfate minerals precipitated by evaporation from solutions and exposed in the solid state to controlled temperature and humidity conditions. The experiments included conditions that were slightly less than Mars atmospheric pressure, as well as other experiments conducted at temperatures from minus 280 degrees Fahrenheit to 77 degrees Fahrenheit and pressures from less than 1/1000 of Earth's atmosphere to ambient pressure.

The researchers used thermogravimetric analysis and isothermal controlled-humidity gravimetric analysis to examine water gain and loss from the samples. They also collected extensive data from X-Ray Diffraction analyses collected while samples were held in an environmental cell at controlled relative humidity and ambient temperature of 77 degrees Fahrenheit inside the diffractometer.

The experiments suggest that studies of martian salts can provide vital information about the hydrogeologic history of Mars and reveal that the return of samples to Earth for detailed study should be an important planetary science research goal. However, the results also show that because of the ease with which dehydration/rehydration transformations take place in the magnesium sulfate salts, the mineralogy might be more accurately characterized in situ before samples are removed from the Mars surface. The research, coupled with previous experience with extra-planetary samples, demonstrates that these and any other environmentally sensitive salts collected on Mars will likely not be returned to Earth in an unmodified state unless exceptional effort is made to preserve martian environmental conditions during sample return.

In addition to Vaniman, the research team included Steve Chipera, Claire Fialips, J. William Carey and William Feldman, all of Los Alamos, as well as former Los Alamos scientist David Bish, now at Indiana University.
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