Pitted cones and domes on Mars: Observations in Acidalia Planitia and Cydonia Mensae using MOC, THEMIS, and TES data

Domes and cones with summit pits located in Acidalia Planitia and Cydonia Mensae were studied using MOC and THEMIS images and a TES-derived thermal inertia map. North of 40.5 degrees N latitude, the features have a dome-like morphology, and south of that latitude, the morphology is more cone-like. Layering is apparent in the summit craters of fresher looking southern cones, and asymmetric aprons were observed in some instances. Some of the northern domes also display layering in their summit craters, but asymmetric aprons were not observed. The northern domes can also display multiple summit pits or no summit pits at all and can occur in association with higher-albedo "pancake" features. The northern domes are higher in albedo but have apparent thermal inertias that are lower than the surrounding plains. The apparent thermal inertia values of the southern cones range from values comparable to the surrounding plains to slightly lower. From the TES thermal inertia map, we infer that the thermal inertia values of the pitted cones are between those of basaltic fine dust and sand, while those of the surrounding plains are closer to that of basaltic sand. While a unique interpretation of the origin of the pitted cones is not possible with the available data, we do not find compelling evidence to suggest an origin related to either basaltic volcanism or ground-ice. Instead, an origin for these features through some combination of mud volcanism and evaporite deposition around geysers and/or springs is most consistent with the observations.