WEATHERING IN ANTARCTIC SOILS AND MARTIAN METEORITES: IMPLICATIONS FOR POSSIBLE LIFE ON MARS

The Dry Valleys of Antarctica are considered to be excellent terrestrial analogs for the environment at the surface of Mars. Because of this, the Dry Valleys have been, and still are, the focus of many areas of research. In a 1983 study [1], weathering products and chemistry were documented at intervals in a soil pit (~80 cm deep) in Wright Valley. We are re-examining that work in view of more recent data from Mars orbital and meteorite studies (note: in 1983, it was not yet established that any meteorites came from Mars). Results of the Wright Valley work seem to be consistent with what is now known or postulated about Mars. Orbital data indicate the presence of water ice just beneath the martian surface [2, 3]. Similarly, in the Wright Valley soil, the water content (-40 to 110 deg C) at the surface is much lower than that at depth, and water decreases upward even within the permanently frozen zone (>40 cm). Water-soluble species in Wright Valley also increase upward. Most changes occur above the permafrost but chemical trends in the Wright Valley soil indicate that aqueous geochemistry is active even in permanently frozen portions. Mars remote sensing data suggest that total amounts of alteration of original igneous rocks on Mars may be low [5]. The top 1-2 cm of the Wright Valley soil is highly depleted in salts compared to the underlying soil, however; it is likely that Mars has analogous characteristics. Mars meteorites have proven that traces of low-temperature aqueous alteration have occurred on Mars [6]; secondary phases in the meteorites are much like those in Wright Valley soil (calcite, Ca-sulfate, halite, and secondary silicates). The extreme variations in composition and mineralogy over a small vertical scale are characteristic of the Wright Valley soil column. Lateral environmental differences in the Dry Valleys also exist. They are responsible for variations in biota; areas lacking life have been apparently identified [5]. The possibility that such small-scale variations are present on Mars should be considered carefully in the search for life there.

[1] Gibson et al (1983) Proc. LPSC 13, A912-A928; [2] Boynton et al. (2002) Science 297, 81; [3] Christensen (2003) 6th Mars Conf. #3126; [4] Wentworth et al. (2003) Astrobio, in revision; [5] Courtright et al. (2001) Ant. Sci. 13, 9.