Mobility of Potassium in Martian Environment

The determination of chemical composition of soils and rocks by the Alpha Particle X-Ray Spectrometers (APXS) at different landing sites revealed a complex geochemical history of Mars with sporadic water activities. In the laboratory, acidic leaching of basaltic shergottites indicated no mobility of K in contrast to a terrestrial basalt, where K was easily leached out. At Meridiani, many geochemical indicators of ancient water processes were found during the Mars Exploration Rover (MER) Mission. APXS measurements of the sediments revealed several elements that also formed compounds with sulfur in the sediments. The concentrations of K in the sediments even point to a starting material with higher K contents than modern soil composition. Also, at the Pathfinder landing site rocks with elevated K concentrations were discovered, higher than the surrounding soil contents. On the Columbia Hills at Gusev crater, some rocks near Home Plate were measured by the MER APXS that showed the highest K concentrations found on Mars, so far. In the plains of Gusev crater, basaltic rocks were encountered that have K concentrations comparable to shergottites. Though, traces of ancient water activities were found. High S enrichments were discovered in disturbed soils on the Columbia Hills, which are not accompanied by elevated K contents. For soils and rocks in general, there are no correlations of K with S. On a global scale, K concentration variations are mostly moderate (factor of about 2) as shown on the K concentration map obtained by the Mars Odyssey Gamma-Ray Spectrometer. Potassium enrichments can be found in the northern lowlands compared to the southern highlands. In spite of the northerly flow direction of numerous channels, the obvious aqueous transport of K from highlands to lowlands is questionable; hence, other means of enrichment have to be considered.