One Martian Year of in Situ Chemistry by the APXS on Board the Mars Exploration Rover Spirit at Gusev Crater

Details One Martian Year of in Situ Chemistry by the APXS on Board the Mars Exploration Rover Spirit at Gusev Crater One Martian Year of in Situ Chemistry by the APXS on Board the Mars Exploration Rover Spirit at Gusev Crater

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p21a0127g&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P21A-0127

Mathematics

Logic

5410 Composition (1060, 3672)

Scientific paper

During the NASA Mars Exploration Rover mission the chemical composition of rocks and soils at Gusev crater was determined by X-ray analysis with the Alpha Particle X-Ray Spectrometer (APXS). From these measurements, concentrations of major, minor, and some trace elements were determined along the rover's traverse. Two distinctive geological regions were explored by the rover Spirit, the Gusev plains and the Columbia Hills. Plains and most of Columbia Hills contain undisturbed soils that are very similar to previous landing sites on Mars. These soils most likely result from global mixing and distribution by large dust storms and local mixing by dust devils. In addition, a meteoritic component was identified in these soils based on enhanced Ni concentrations, which are caused by continuous bombardment of the martian surface by either stony and/or iron meteorites. Rocks in the plains revealed thin weathering rinds of compositions different from their interior. Fresh surfaces (exposed by the Rock Abrasion Tool) resemble volcanic rocks of primitive basaltic composition with low intrinsic K contents. Along the rover's traverse, several trenches were excavated by the rover wheels. Significant increase in Mg, S, and Br was found in one trench compared to the topmost surface soil composition, which could result from water that once percolated through subsurface layers and deposited salts. In Columbia Hills, a variety of different rock compositions was found that differ markedly from the primitive basalts of the plains. Most of the Columbia Hill rocks show enrichments in P, S, Cl, K, Ti, Ni, and Br compared to the plain basalts, while Cr and Fe are always depleted. Many Columbia Hill rocks are significantly weathered and altered compared to the plain basalts. Even after grinding of the Columbia Hill rock surfaces to a depth of up to 1 centimeter, there was a high abundance of salts as indicated by the abundance of S, Cl, and Br. The P contents in brushed and abraded surfaces of P-rich rocks are an indicator for alteration rinds. Assuming the mineral apatite is the main host phase for P acidified water could have easily leached P from the rock surfaces, yet not altered most resistant feldpars. Disturbed soils can be similar to undisturbed ones or completely different, such as the soil 'Paso Robles' in the Columbia Hills. These samples have the highest abundance of sulfates on Mars, thus far. Soils and rocks in the Columbia Hills show clear evidence of ancient aqueous environments.

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