Martian Sand Dunes as Natural Ice Sensors: How to Identify Ice Composition From Dune‐Ice Morphology

Abstract

The seasonal exchange of martian volatiles between the atmosphere and surface drives the formation and modification of gullies, spiders, and other surface features on Mars. Studies of such seasonal ice‐driven activity rely on correct interpretations of ice composition and coverage. However, data sets that discriminate ice composition often have coarse resolution or limited spatial coverage. In this work, we investigate whether the surface morphological patterns of seasonal ice on sand dunes reflect different ice compositions and thus could be used to interpret the meter‐scale ice environment over the dunes. Using HiRISE images collected over sand dunes in the northern mid‐latitudes (30–65°N), we grouped observations by patterns in dune‐ice morphology and interpreted the ice composition of each group. Interpretations of ice composition were then compared to the ice compositions derived from coincident thermal and spectral observations. We found that dune ice with both a high surface brightness and sublimation spots or cracks corresponded to CO ₂ ice, whereas dunes that exhibited increased surface brightness without sublimation spots or cracks corresponded to H ₂ O ice. These interpretations are corroborated by prior seasonal ice cap mapping results, surface temperature observations, and the position of spectrally derived seasonal ice cap edges, despite orders‐of‐magnitude differences in data set resolution. This work provides a new opportunity to probe the martian seasonal H ₂ O cycle while also improving landform‐scale ice composition interpretations for studies of surface features thought to form from ice‐regolith interactions.