AEOLIAN BEDFORMS AT THE EXOMARS ROSALIND FRANKLIN ROVER LANDING SITE

Meter-to kilometre-scale aeolian bedforms (ripples and dunes) are common on Mars and recent observations show that many are actively migrating. The ExoMars Rosalind Franklin Rover landing site, Oxia Planum, in northwest Arabia Terra, contains few kilometre-scale duneforms, but many metre-scale ‘ripple-like’ bedforms. We have studied the Oxia Planum site to measure the diversity and population density of these features, aiming to understand both the sediment transport history of the site, and whether aeolian bedforms pose a traversability hazard to the mission. We analysed high-resolution (25 cm/pixel) orbital remote sensing data using: (i) a machine-learning system and human mapping of meter-scale bedforms, (ii) in-situ analogue 3D profiling studies from previous Rover missions, (iii) atmospheric models, and (iv) a systematic survey of bedform azimuths to determine formative wind directions.

We find that larger bedforms (~>10 m across-bedform length) are common only within topographically enclosed spaces such as larger impact craters, but smaller (1-5 m across) ripple-like bedforms occur across the region, especially in the eastern part of the site. The larger bedforms generally form continuous patches of up to a few tens of bedforms, but the more common smaller bedforms occur as widespread discontinuous fields of 100s-1000s of individual bedforms. By analogy with measurements of similar bedforms made using Mars Exploration Rover-Opportunity data, we suggest that the smaller bedforms have crest heights of approximately 1/15^th of their across-bedform length. Thus the numerous bedforms here that are 3-4 m across will have crest heights of only ~25 cm and should not pose a significant traversability hazard.

Almost all ripple-like bedforms in the study region have a consistent ~NE-SW azimuth, with no azimuth difference between larger and smaller bedform populations. We find little correspondence between aeolian bedform azimuth and present-day wind directions determined from a suite of Global Climate Model runs. We infer that the bedforms formed under wind conditions different than today’s. We infer also that they are not currently active; if they were active, we would expect the smaller bedforms (that adapt more quickly to changing wind conditions) to have a different azimuthal trend to the larger examples. We conclude that the Oxia Planum aeolian bedforms are a relic of a different wind regime – although testing this result will require in-situ measurement when Rosalind Franklin begins its surface mission in 2023.