HiRISE observations of fractured mounds: Possible Martian pingos

Early images from the High Resolution Imaging Science Experiment (HiRISE) camera have revealed small fractured mounds in the Martian mid-latitudes. HiRISE resolves fractures on the mound surfaces, indicating uplift, and shows that the mound surface material resembles that of the surrounding landscape. Analysis of Mars Orbiter Camera (MOC) images shows that in Utopia Planitia the mounds lie almost exclusively between 35-45°N. This range coincides with the peak-abundance latitudes of several landforms attributed to ground water or ice, including gullies, and suggests a ground ice-related origin. The best terrestrial analogues for the observed mound morphology are pingos, although some differences are noted. The presence of uncollapsed. pingos would indicate the presence of near-surface ground ice in the Martian mid-latitudes, at depths greater than the ∼1 meter sampled by orbital spectrometers. Pingo formation may require near-surface liquid water, which is consistent with a shallow groundwater model for the origin of gullies.