Aeolian Transport of Coarse Sediment in the Modern Martian Environment

Introduction: Evidence of aeolian sandstone outcrops, migrating sand dunes, and changes in surface albedo changes caused by redistribution of surface dust on Mars demonstrate that aeolian processes have been and continue to be a dominant agent of surface modification [3] [7] [9]. It is known that strong wind events on Mars can be responsible for lifting large amounts of sediment into the atmosphere. Entrained dust can significantly decrease optical visibility and saltation of sand can cause large amounts of particle splash due to Mars’ low gravity. For these reasons, and many more, the effects of surface wind need to be carefully considered for any mission to Mars. Ensuring that instruments remain operational in these conditions requires a full understanding of the modern-day aeolian processes. Yet, transport within Mars’ low atmospheric pressure environment is still not fully understood and requires a combination of modeling, experiments, and ground truth observations [1] [4] [6]. Here we present results from a series of systematic change detection campaigns conducted by Curiosity over three Martian years (site locations shown on basemap in Figure 1). These results include the first-ever observations of coarse-grained (1-3mm) sediment transport in the modern Martian environment. These unforeseen results are particularly noteworthy -and potentially enigmaticgiven the frequency with which grain motion occurs and the overall wind strength implied by standard saltation models. For this reason, the motion of coarse sediment likely requires an alternate explanation, such as strong but infrequent wind gusts or impact-driven creep by smaller, saltating particles. Identifying how wind transports coarse sand grains in the modern Martian environment is important for understanding the danger that sediment-lifting events pose for robotic instruments as well as for future human exploration. Our results confirm that winds are most active during Southern Summer on Mars, and ongoing work is focused on classifying diurnal variations in wind activity. Direct imaging of surface sediments changes is useful for collecting information on the strength, frequency and duration of individual wind events, all of which can be used to keep future explorers safe. These results can also be used to test and improve general circulation models. Methods: Change detection. The primary component of this research study was visual inspection of Mastcam images (M100 camera) taken along the Curiosity traverse (between Sol 176 and Sol 1498). At each site in question, the rover was stopped for an extended period of time to conduct various in situ rock analyses or for solar conjunction events. At each site, we acquired a set of images right after ingress and right before egress; the “before” and “after” images are separated by anywhere from 8 to 100 sols, depending on the site.