Recent insights into dust lifting and sand motion at the surface of Mars.

The last decade has seen data on surface dust lifting and sand motion returned (and released publicly) by four Mars surface missions (Opportunity, Mars Science Laboratory [MSL], InSight, and Mars 2020) and from surface-viewing instruments on several orbiters (e.g., MARCI and THEMIS on Mars Odyssey, HRSC on Mars Express, CTX and HiRISE on the Mars Reconnaissance Orbiter, MCC on the Indian Mars Orbiter Mission, and EXI on the Emirates Mars Mission). These observations range from mapping surface dust rearrangement during years with and without global dust storms, to linking modern near-surface winds to active aeolian features, to ideas about how sand and dust motion is initiated, to exploring the balance between dust lifting by different processes. The last decade has also seen new experiments related to grain motion on Mars using wind tunnels, including new definitions of motion thresholds and the first low-gravity wind tunnel measurements, and many advances in the theory and numerical modeling of grain motion and aeolian feature formation. Finally, the last decade has seen greater use of global, mesoscale, and large eddy simulations using atmospheric models to help interpret observations of dust lifting and sand motion, including exploring possible past climate interpretations of inactive aeolian or sedimentary rock features that do not match winds observed or predicted in the present epoch. This presentation attempts to briefly summarize what has been learned over the last decade, as well as pointing to ongoing mysteries, debates, and areas where further investigation is most needed.

Figure: (A) ~2 cm changes in ripple crest positions between sols 1260 (blue) and 1265 (red) of the Spirit rover mission in Front Hazcam images (Sullivan et al., 2008). (B) and (C): ~cm changes in ripple crest positions between sols 1602 and 1604 of the MSL mission, in Mastcam images taken in southern summer in Gale crater. Image alignment and annotation by Mariah Baker, credit NASA/JPL-Caltech/MSSS. (D) Enhanced Navcam image of a dust devil in Gale crater on sol 2847 of the MSL mission, image credit NASA/JPL-Caltech/SSI. (E)-(G): Stretched color Navcam images (taken 14 s apart) showing a huge "gust lifting" event in Jezero crater on sol 117 of the Mars 2020 mission, image credit NASA/JPL-Caltech/SSI.