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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, E02S20, doi:10.1029/2005JE002490, 2006

Aqueous processes at Gusev crater inferred from physical properties of rocks and soils along the Spirit traverse

N. A. Cabrol

Space Science Division, NASA Ames Research Center, Moffett Field, California, USA
SETI Institute, Mountain View, California, USA


J. D. Farmer

Department of Geological Sciences, Arizona State University, Tempe, Arizona, USA


E. A. Grin

Space Science Division, NASA Ames Research Center, Moffett Field, California, USA
SETI Institute, Mountain View, California, USA


L. Richter

DLR Institut für Raumsimulation, Cologne, Germany


L. Soderblom

U.S. Geological Survey, Flagstaff, Arizona, USA


R. Li

Department of Civil and Environmental Engineering and Geodetic Science, Ohio State University, Columbus, Ohio, USA


K. Herkenhoff

U.S. Geological Survey, Flagstaff, Arizona, USA


G. A. Landis

Photovoltaics and Space Environment Branch, NASA John Glenn Research Center, Cleveland, Ohio, USA


R. E. Arvidson

Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri, USA


Abstract

Gusev crater was selected as the landing site for Spirit on the basis of morphological evidence of long-lasting water activity, including possibly fluvial and lacustrine episodes. From the Columbia Memorial Station to the Columbia Hills, Spirit's traverse provides a journey back in time, from relatively recent volcanic plains showing little evidence for aqueous processes up to the older hills, where rock and soil composition are drastically different. For the first 156 sols, the only evidence of water action was weathering rinds, vein fillings, and soil crust cementation by salts. The trenches of Sols 112–145 marked the first significant findings of increased concentrations of sulfur and magnesium varying in parallel, suggesting that they be paired as magnesium-sulfate. Spirit's arrival at West Spur coincided with a shift in rock and soil composition with observations hinting at substantial amounts of water in Gusev's past. We used the Microscopic Imager data up to Sol 431 to analyze rock and soil properties and infer plausible types and magnitude of aqueous processes through time. We show the role played early by topography and structure. The morphology, texture, and deep alteration shown by the rocks in West Spur and the Columbia Hills Formation (CHF) suggest conditions that are not met in present-day Mars and required a wetter environment, which could have included transport of sulfur, chlorine, and bromine in water, vapor in volcanic gases, hydrothermal circulation, or saturation in a briny fluid containing the same elements. Changing conditions that might have affected flow circulation are suggested by different textural and morphological characteristics between the rocks in the CHF and those of the plains, with higher porosity proxy, higher void ratio, and higher water storage potential in the CHF. Soils were used to assess aqueous processes and water pathways in the top layers of modern soils. We conclude that infiltration might have become more difficult with time.

Received 11 May 2005; accepted 12 December 2005; published 22 February 2006.

Keywords: alteration; aqueous processes; Mars; Microscopic Imager; weathering.

Index Terms: 5415 Planetary Sciences: Solid Surface Planets: Erosion and weathering; 5470 Planetary Sciences: Solid Surface Planets: Surface materials and properties; 6225 Planetary Sciences: Solar System Objects: Mars.

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Citation: Cabrol, N. A., J. D. Farmer, E. A. Grin, L. Richter, L. Soderblom, R. Li, K. Herkenhoff, G. A. Landis, and R. E. Arvidson (2006), Aqueous processes at Gusev crater inferred from physical properties of rocks and soils along the Spirit traverse, J. Geophys. Res., 111, E02S20, doi:10.1029/2005JE002490.