Characterizing Candidate Pingo Morphology on Ceres
NASA’s Dawn Mission has been exploring Ceres since arrival in 2015. However, recent low-altitude Dawn orbits during its second extended mission (XM2) have brought the spacecraft as low as 35 km above the surface of Ceres, collecting an abundance of new high-resolution imaging data with the Framing Camera including possible evidence of pingos in Occator crater. On Earth, pingos and other frost-heaves are a product of groundwater flow and freezing that create an ice-cored mound (e.g., Burr et al. 2008). An open-system pingo has a supply of water, where the groundwater is under artesian pressure, which causes uplift, and creates an ice core underneath the permafrost (Soare et al. 2014, Vasil’chuk et al. 2016). Contrastingly, the closed-system has a limited water supply that freezes and pushes sediments up into a dome, as hydrostatic pressure grows the ice lens. This can cause collapse or ruptures at the top of the pingo due to expanding or fluid material. Most terrestrial pingos are ~100 m in diameter but can grow up to 2 km (Burr et al. 2008). Candidate pingos on Mars range 20-1000 m (Burr et al. 2008), and thus comparisons between Ceres and these larger planets are possible. Preliminary imaging results show ~170 domical features where some are candidate pingos. These formations could be evidence of frost heave, given that Ceres’ gravity could facilitate frost heaving (e.g., Sizemore et al. 2018), and likely emplacement of large-scale flows consisting of silicate materials entrained in melted ice during Occator’s formation. Out of all the mounds there are 76 features with apex depressions or pointed peak that are pingo candidates. Further, 55 of the 76 features have slopes under 45º, making them the strongest pingo candidates. In addition, there are approximately 15 features that are morphologically similar, but that require further investigation to disambiguate any relationship with frost heaving. Two large pingo candidates are ~500 m in diameter, and Occator’s central dome ~2 km wide is also a candidate. Several candidates have potential flows associated with or emanating from them. Observations also show other evidence of ground ice on Occator’s crater floor. These new imaging results help shed light on possible ground ice and periglacial analogs and will provide new ways to test hypotheses regarding both subsurface ice as well as the formation and evolution of large impacts on Ceres.