SURVEYING MEGA-RIPPLE MIGRATION ON MARS

Recent analysis of intermediate-sized aeolian bedforms, termed “mega-ripples”, has revealed that some of these landforms are currently migrating on Mars today. This finding was somewhat unexpected as prior surveys showed no movement and, in some cases, craters superposed on the bedforms. Mega-ripples have greater dimensions (1-35 m spacing, 0.8-2 m tall) and brighter crests than typical dark ripples (1-5 m spacing, ~0.4 m tall). Silvestro et al. (2020) demonstrated that two dune fields in Syrtis Major and Mawrth Vallis host migrating mega-ripples. That study used repeat HiRISE images (0.25 m/pix) to show mega-ripple fluxes were two orders of magnitude lower than local dunes. Some of these mega-ripples resemble and overlap in size with Transverse Aeolian Ridges (TARs; 10-100 m spacing, 1-14 m tall), which are widely considered to be remnant landforms.

Here we describe a preliminary effort to expand the current inventory of active mega-ripple/TARs by surveying changes in long-baseline (up to 6 Mars years) HiRISE orthoimage series. Ultimately this investigation will test the hypothesis that many mega-ripples and TARs are migrating in the current climate and can be readily identified based on their boundary conditions and proximity to high sand flux areas.

It was found that 14 of the 54 dune fields (~26%) investigated by Chojnacki et al. (2019) host migrating bedforms with characteristics consistent with mega-ripples. These detections were typically near high sand flux dunes, including certain north polar sites which have limited seasonality. However, that report was focused on migrating dune systems and mega-ripple activity was merely noted if present. We are currently starting a systematic survey of low to high sand flux sites, utilizing the longest available baseline HiRISE pairs, examining wide areas both proximal and distal to dunes. Locations will include well-characterized TAR sites like Ius Chasma and Gamboa crater (Zimbelman, 2010; 2019), along with areas that yielded inconclusive results from earlier analysis (Silvestro et al., 2010). We will present updated results at the conference.

Acknowledgments: This research was supported by NASA MDAP 80NSSC20K1066 and the HiRISE/MRO mission. D. Vaz acknowledges CITEUC's support (UID/Multi/00611/2019) and FCT Grant CEECIND/02981/2017.

References: Silvestro S. et al. (2020) JGR, 2020JE006446. Chojnacki M. et al. (2019) Geology, G45793.1. Zimbelman J. R. (2010) Icarus, 121, 22–291. Zimbelman J. R. (2019) Icarus, 333, 127–129. Silvestro S. et al. (2011) GRL, 38, L20201.