A model for formation of dust, soil, and rock coatings on Mars: Physical and chemical processes on the Martian surface

Abstract

[1] A model is presented here to explain the generation of surface material on Mars using chemical, magnetic, and spectroscopic data from Mars and geologic analogs from terrestrial sites. One basic premise is that the dust/soil units are not derived exclusively from local rocks, but are rather a product of global, and possibly remote, weathering processes. Another assumption in this model is that there are both physical and chemical interactions of the atmosphere with dust particles and that these two processes create distinctly different products. Physical processes distribute dust particles on rocks and drift units, forming physically aggregated layers; these are reversible processes. Chemical reactions of the dust/soil particles create alteration rinds on rock surfaces and cohesive, crusted surface units between rocks, both of which are relatively permanent materials. According to this model the dominant components of the dust/soil particles are derived from alteration of volcanic ash and tephra and contain primarily nanophase and poorly crystalline ferric oxide/oxyhydroxide phases as well as silicates. These phases are the alteration products that formed in a low-moisture environment. These dust/soil particles also contain a smaller amount of material that was exposed to more water and contains crystalline ferric oxides/oxyhydroxides, sulfates, and clay silicates. These components could have formed through hydrothermal alteration at steam vents or fumeroles, thermal fluids, or through evaporite deposits. Wet/dry cycling experiments are presented here on Mars soil analogue mixtures containing poorly crystalline and crystalline components dominated by nanophase to $2 mm diameter particles. Cemented products of these soil mixtures are formed in these experiments, and variation in the surface texture was observed for samples containing smectites, nonhydrated silicates, or sulfates. Reflectance spectra were measured of the initial particulate mixtures, the cemented products, and ground versions of the cemented material. The spectral contrast in the visible/near-infrared and midinfrared regions is significantly reduced for the cemented material compared to the initial soil and somewhat reduced for the ground, cemented soil compared to the initial soil. The results of this study suggest that transient fluvial activity on Mars will have a profound effect on the texture and spectral properties of the dust/soil particles on the surface. The model developed in this study provides an explanation for the generation of cemented or crusted soil units and rock coatings on Mars and may explain albedo variations on the surface observed near large rocks or crater rims.

A new view of dark Martian regions from geomorphic and spectroscopic analysis of Syrtis Major

“…The occurrence in large proportion of magnetite (or titanomagnetite) in the low albedo region of Syrtis is also consistent with the observation of a significant proportion of magnetic grains in brighter regions of Mars like in the landing site of Pathfinder (e.g., Gunnlaugsson et al 2002). Alternatively, the surface composition derived here may result from regional alteration processes (e.g., Bishop et al 2002). Finally, this work gives new evidence of the presence of dark mantle of silt sized material on the surface of Mars was already identified by past photopolarimetric, geomorphic and thermophysical observations compiled by Edgett & Malin (2000).…”

Multispectral imaging from Mars Pathfinder

“…Downwind rock faces typically appeared dustier. The types of rock coatings observed by the IMP have since been used to draw inferences about past environments in the vicinity of the landing site (McSween et al, 1999;Barnouin-Jha et al, 2000;Bishop et al, 2002).…”

“…A related model was developed by Bishop et al(2002) using a combination of IMP spectral data, APXS chemical results, results from the MPF magnet experiment (Madsen et al, 1999), and laboratory studies of martian analog materials to study the nature of the bright drifts, possibly cemented or indurated soils, and rock coatings observed at the MPF landing site. They suggested that mobile dust particles can account for the spectral and chemical properties of bright drifts observed at the MPF landing site and that this same dust, containing reactive sulfate and/or ferric oxyhydroxide phases, has also coated the rocks.…”

Science Priorities for Mars Sample Return

“…Recently, it has been suggested that the suites of minerals found at the surface of Mars (including silica and sulfates) could be related to hydrothermal/fumarolic activity (e. g. Bishop et al, 2002;Yen et al, 2007;Squyres et al, Science, submitted). Hydrothermal activity is to be expected because volcanic activity has occurred at the surface within the last couple of million years, demonstrating that active heat sources still exist (Neukum et al, 2004).…”