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Mars: Letters
Nature 436, 66-69 (7 July 2005) | doi:10.1038/nature03640; Received 18 November 2004; Accepted 8 April 2005
Water alteration of rocks and soils on Mars at the Spirit rover site in Gusev crater
Larry A. Haskin1,18, Alian Wang1, Bradley L. Jolliff1, Harry Y. McSween2, Benton C. Clark3, David J. Des Marais4, Scott M. McLennan5, Nicholas J. Tosca5, Joel A. Hurowitz5, Jack D. Farmer6, Albert Yen7, Steve W. Squyres8, Raymond E. Arvidson1, Göstar Klingelhöfer9, Christian Schröder9, Paulo A. de Souza, Jr10, Douglas W. Ming11, Ralf Gellert12, Jutta Zipfel12, Johannes Brückner12, James F. Bell, III8, Kenneth Herkenhoff13, Phil R. Christensen6, Steve Ruff6, Diana Blaney7, Steven Gorevan14, Nathalie A. Cabrol15, Larry Crumpler16, John Grant17 & Lawrence Soderblom13
Abstract
Gusev crater was selected as the landing site for the Spirit rover because of the possibility that it once held a lake. Thus one of the rover's tasks was to search for evidence of lake sediments1. However, the plains at the landing site were found to be covered by a regolith composed of olivine-rich basaltic rock and windblown 'global' dust2. The analyses of three rock interiors exposed by the rock abrasion tool showed that they are similar to one another, consistent with having originated from a common lava flow3, 4, 5, 6, 7, 8. Here we report the investigation of soils, rock coatings and rock interiors by the Spirit rover from sol (martian day) 1 to sol 156, from its landing site to the base of the Columbia hills. The physical and chemical characteristics of the materials analysed provide evidence for limited but unequivocal interaction between water and the volcanic rocks of the Gusev plains. This evidence includes the softness of rock interiors that contain anomalously high concentrations of sulphur, chlorine and bromine relative to terrestrial basalts and martian meteorites9; sulphur, chlorine and ferric iron enrichments in multilayer coatings on the light-toned rock Mazatzal; high bromine concentration in filled vugs and veins within the plains basalts; positive correlations between magnesium, sulphur and other salt components in trench soils; and decoupling of sulphur, chlorine and bromine concentrations in trench soils compared to Gusev surface soils, indicating chemical mobility and separation.
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