Sand Flux Results for Aeolian Dunes at Current and Candidate Landing Sites on Mars

Abstract:

It is now known unambiguously that wind-driven bedform activity is occurring on Mars today. It has also been demonstrated the rapid aeolian abrasion of sedimentary deposits that potentially host ancient habitable environments may provide the best mechanism for exposing samples containing relatively undegraded organics (Farley et al. 2014). Thus, current processes operating on the surface of Mars are highly relevant to our understanding of the past.

Here, we discuss new sand flux results of active dune across Mars, including several current and candidate landing sites with Meridiani Planum, Gale crater, Valles Marineris, and Mawrth Vallis. For this task, we have utilized multi-temporal images acquired annually by the HiRISE camera (25 cm/pixel) along with co-located HiRISE Digital Terrain Models.

Falling dunes in Coprates Chasma (Mars 2020 candidate landing site) measuring 6–10 meters in height were detected migrating on average 0.5 m per Earth year, yielding crest fluxes of 3.1 m³ m^-1 yr^-1 (units hereafter assumed). Barchans near the MSL rover at Gale crater have slightly lower fluxes of 1.2, while earlier work in Endeavour crater, the current site of the Opportunity Rover, showed dome dunes with fluxes as high as 13 (average of 6.8; Chojnacki et al. 2015). New results of Mawrth Vallis (Mars 2020 candidate) dunes suggest these high rates are not uncommon, as barchans there possess average fluxes of 11.5. Assuming ripple reptation rates are 1/10^th that of crest fluxes, total flux (saltation plus reptation) would range 3.2 to 12.7 m³ m^-1 yr^-1 for all sites studied herein.

Active dunes and the abrasion susceptibility (Sa) of local rocks are relevant to assess how sand fluxes modify the landscape. Using the methodology and assumptions (Sa for basalt, mean trajectory height etc.) described in Bridges et al. (2012), we estimated abrasion rates of local basaltic bedrock. For example, sand blasting at Mawrth Vallis is estimated to produce 2–8 μm/yr for flat ground and 15–75 μm/yr for a vertical rock face. These rates would be even higher for the clay-rich units that have been previously documented there. Understanding these processes may prove vital to locating ancient habitability sites for in situ exploration where organic-bearing material is most likely to be recently exposed and thus not yet broken down by radiation.