Recent Observations of Recurring Slope Lineae on Mars

Details Recent Observations of Recurring Slope Lineae on Mars Recent Observations of Recurring Slope Lineae on Mars

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p21d..01m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P21D-01

Biology

[5200] Planetary Sciences: Astrobiology, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Recurring slope lineae (RSL) are relatively low-albedo features that extend down steep slopes from bedrock outcrops, often associated with small channels, and hundreds of them may form in rare locations (McEwen et al., 2011, Science 333, issue 6062). RSL appear and lengthen incrementally in the late southern spring/summer from 52°S to 32°S latitudes, favoring equator-facing slopes--times and places with peak surface temperatures from ~250-300 K. Liquid brines near the surface might explain this activity, but the mechanism and source of water are not understood. MRO's High Resolution Imaging Science Experiment (HiRISE) provides the primary dataset for observing these meter-scale features. RSL are recurring-forming and growing in the warm season (late spring to early fall) then fading, sometimes completely vanishing in cold seasons. Intensive monitoring during the current southern summer is continuing to reveal new details, best seen in a set of animated GIFs at http://hirise.lpl.arizona.edu/sim. These recent observations show that individual flows fade at different rates, and may fade even in the summer while others are growing. Fading of individual flows (but not adjacent flows) may occur in only 2 weeks. There are significant interannual variations in the abundances, lengths, and exact locations of the RSL. In contrast, candidate RSL sites in equatorial regions (18°S to 19°N) have not shown continued activity, and are probably not the same type of activity or are much less active. Laboratory experiments by Conway et al. (Icarus 211, 443) provide new insights into how surface water flows behave at Martian atmospheric pressures and typical temperatures. The pure water boils, rapidly evaporating and simultaneously freezing in the shallow subsurface. Although salty water is not so volatile, this may help to explain why no water bands are seen in CRISM observations-water is actually exposed at the surface for very short periods of time over small areas, and rapidly evaporates to leave a dry surface layer. Surface ice would not form at the temperatures where RSL are active, but should form in the shallow subsurface. This shallow ice prevents further infiltration and makes the water flow downhill faster. Further laboratory experiments are needed to attempt to reproduce the darkening and fading of RSL, and to confirm that water bands are not likely to be detected by CRISM.

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