Investigating a Link Between Topography and Scalloped Depressions in Utopia Planitia, Mars

Western Utopia Planitia, located in the northern plains of Mars, is home to a myriad of possible periglacial landforms. One of these is scalloped depressions, defined primarily by their oval-shape and north-south asymmetry, including both pole-facing “steps” and an equator-facing slope. Scalloped depressions are thought to have formed through sublimation of ground ice in the Late Amazonian, consistent with the hypothesis that Mars is presently in an interglacial period marked by the poleward retreat of mid-latitudinal ice. The directional growth of scalloped depressions was mapped within the region and present a correlation between topography and scalloped depression development. It was determined that topography appears to play a role in scallop development, as noted by the most-densely scalloped region residing among a lower spatial density of craters previously mapped by Harrison et al. (2019). Within this region, scallops were also observed to be absent atop crater ejecta, but present atop crater ejecta in other regions of the study area. A large majority of scallops maintain a north-south asymmetry and observed changes in geomorphology that range from predominantly smoother terrain in the northern latitudes to very hummocky terrain dominated by possible periglacial features as latitude decreases. Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images were primarily used, with a few images coming from the MRO High Resolution Imaging Science Experiment (HiRISE). Observations are consistent with previous studies showing the overall density of scalloped depressions decreases with increasing latitude, with the majority exhibiting steps facing in a poleward direction. The majority of scallops observed to have steps in a non-poleward direction occur within in ice-rich regions mapped by Stuurman et al. (2016). It was ultimately concluded that scallops demonstrating poleward-facing steps likely formed during periods of high obliquity on Mars in the Late Amazonian, while scallops within the ice-rich regions potentially formed at a greater range of obliquities.