Spectral Study of Water Tracks as an Analog for Recurring Slope Lineae

Liquid water is a key requirement for life on Earth, and serves as an important constraint on present day habitability on Mars. Recurring Slope Lineae (RSL) are a unique phenomenon on Mars that may be formed by brine seeps. Their morphological, seasonal and temporal characteristics support this hypothesis; however, spectral evidence has been lacking. Ojha et al., 2013 recently analyzed CRISM images from all confirmed RSL in the southern mid-latitudes and equatorial regions and found no spectro-scopic evidence for water. Instead, enhanced abun-dances or distinct grain sizes of both ferric and ferrous minerals are observed at most sites. The strength of these spectral signatures changes as a function of sea-son, possibly indicating removal of a fine-grained sur-face component during RSL flow, precipitation of fer-ric oxides, and/or wetting of the substrate. Water tracks (WT) have been suggested as a terrestrial analog for RSL by Levy et al., 2011. WT are defined as dark surface features that extend downslope in a linear or branching fashion, usually oriented along the steepest local gradient, in the Dry Valleys of Antarctica. They can be 1-3 m in width and can have lengths up to 2 km. They share many morphological and seasonal characteristics with RSL including active growth during summer seasons and fading during winter. Snowmelt, ground ice melt and deliquescence by hygroscopic salts have been suggested as possible formation mechanisms for water tracks. No spectral work to date has been reported for water tracks