Comparison of the phoenix mars lander wcl soil analyses with antarctic dry valley soils, mars meteorite EETA79001 sawdust, and a mars simulant

摘要

The results of the Mars Phoenix Lander's Wet Chemistry Laboratory (WCL) for the analyses of the soluble ionic species present in the soil at the northern polar plains of Mars are compared to soil from the Antarctic Dry Valleys (ADVs), martian meteorite EETA79001 sawdust, and a Mars simulant. The ADV soil was compared to the Phoenix site by averaging the samples at analogous 0-5cm depths and also all the samples from the pavement to the ice-table. Results from each analysis reveal similar ion concentrations ranging plus or minus one order-of-magnitude for all ions except perchlorate (ClO4-), which was three orders-of-magnitude greater in the Phoenix soil. The pH and solution electrical conductivity were also found to be similar for the ADV and Mars soils. The ADV profiles confirm that ClO4- gradients are sensitive indicators for the presence and form of liquid H_2O on both Earth and Mars. The Phoenix and meteorite samples contained similar species and ratios but the meteorite concentrations were on average ~4% of those for the Phoenix soil. The only exception was the ~16% higher level of Ca~(2+) in the meteorite due to the CaCO_3 druse. The ADV results imply that the Phoenix site is significantly more arid than University Valley, and has been for a greater period of time, as evidenced by the lack of salt gradients and the age of the soils. A Mars simulant was also formulated according to a MINEQL equilibrium model of the WCL results, and its analysis provides confidence that the soluble composition and parent salts at the Phoenix site are reasonably constrained. Overall, comparison of these samples of soil and sawdust indicates that not only does the martian meteorite EETA79001 contain similar soluble ionic species as the martian soil from the northern polar plains, but also that the soils from the ADV are similar to both, thus strengthening the argument for the ADV as a suitable terrestrial Mars analog environment.