DO MARTIAN HILLSLOPES WITH RECURRING SLOPE LINEAE (RSL) EXPERIENCE ENHANCED BEDROCK WEATHERING RATES?

Recurring Slope Lineae (RSL) are dynamic, low-albedo, slope-parallel surface features on Mars that typically occur on steep (>25°) slopes. RSL often display seasonal dynamics as they appear during late Martian spring, progressively grow during summer, and subsequently fade as summer ends. RSL formation mechanisms remain under debate with proposed mechanisms involving either water/brines (‘wet theories’) vs. dry granular flows within a surficial dust layer (‘dry theories’). In an attempt to distinguish between plausible RSL mechanisms, this study examined morphologic and topographic proxies for rock weathering intensity on adjacent RSL vs. non-RSL hillslopes within three craters: Corozal (39°S, 159°E), Garni (12°S, 290°E) and Rauna (35°N, 328°E). We hypothesize that increased rock weathering intensity on RSL hillslopes would argue against the ‘dry’ RSL mechanisms as RSL dynamics within a thin dust layer are not expected to significantly impact bedrock weathering. In contrast, the presence of water or brines on RSL hillslopes could conceivably contribute to increased rock weathering rates.

To test for potential variability in rock weathering intensity between RSL vs. non-RSL hillslopes we used HiRISE images to map the fracture characteristics of bedrock outcrops and HiRISE-CTX Digital Elevation Models (DEMs) to measure hillslope-scale variability in topographic attributes, such as slope distribution and curvature. Our results revealed increased rock weathering intensity for RSL hillslopes at Corozal and Garni and no detectable differences in weathering intensity between RSL and non-RSL hillslopes at Rauna. Thus, slope morphology appears to support a ‘wet’ formation mechanism for at least some of the Martian RSL.