The dynamic nature and spectral characteristics of low-albedo slope streaks on Mars and their possible hydrologic implications
Amit Mushkin1,2, David E Stillman3, Alan R Gillespie4, David R Montgomery4, B. C. Schreiber4 and Charles Hibbitts5, (1)University of Washington Seattle Campus, Seattle, United States, (2)Geological Survey of Israel, Jerusalem, Israel, (3)Southwest Research Institute, Boulder, CO, United States, (4)University of Washington Seattle Campus, Seattle, WA, United States, (5)Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States
Abstract:
Low-albedo down-slope streaks that form repeatedly within weekly time-scales and subsequently fade over seasonal to decadal periods are commonly observed in the tropical and mid-latitudes of Mars. ‘Dry’ mass-wasting processes vs. ‘wet’ modification of the surface by aqueous phases are the mechanisms typically considered to explain their formation. Recently, high frequency HiRISE image time-series of seasonal recurrence, incremental growth and fading of small (meter-decameter scale) slope streaks, also termed ‘recurring slope lineae’ (RSL), have been presented in support of a ‘wet’ origin likely associated with brine seepage. Here, we present new results that demonstrate comparable recurrence, incremental growth and fading characteristics over yearly time-scales for decameter-kilometer scale low-albedo slope-streaks in Lycus Sulci, Amazonis Planitia and Arabia Terra. These dynamic characteristics support the previous association of low-albedo slope streaks with brine seepage based on their geomorphic and spectral relations with surrounding unaffected slopes.
Low-albedo slope streaks are typically not associated with detectable erosion or terminal, down-slope depositional activity at the resolution of 25 cm/pixel HiRISE images. CRISM observations consistently indicate that darkened slope-streak surfaces are spectrally enriched in FeOx and are void of detectable water/ice spectral absorption bands. Thus, the liquid seeps considered for the formation of meter to kilometer scale slope streaks are likely low-volume transient events that evaporate and/or freeze and sublime leaving behind a meta-stable dry precipitate that ‘stains’ the surface dark and may provide insights into the possible composition of such brines.
Slope streak formation through a ‘wet’ brine seepage mechanism supports the possible presence of pressurized sub-surface aquifers that may be released via faults or cracks able to produce recurring transient discharge events during favorably warm daily/seasonal surface conditions. First-order calculations for the liquid volumes that would be associated with such transient brine extrusions suggest the presence of regional-scale extensive aquifers and/or effective recharge mechanism for local-scale aquifers perhaps during high obliquity periods.
