Geologic mapping of the Ac-2 Coniraya quadrangle of Ceres from NASA's Dawn mission: Implications for a heterogeneously composed crust

Abstract

Since its arrival at Ceres, Dawn's Framing Camera has been imaging the dwarf planet at different altitudes, using 8 different filters. Based on these images, global clear filter mosaics, digital terrain models, and global color mosaics were produced. These datasets are basis for the derived photo-geologic map of the Ac-2 Coniraya quadrangle, located between 0° and 90° eastern longitude and between 20° and 40° northern latitude. Crater size-frequency distribution (CSFD) measurements have been applied to derive the stratigraphic history of the identified geologic units in the Ac-2 Coniraya quadrangle. Based on these investigations, we found that the Ac-2 Coniraya quadrangle shows evidence for a long geologic history lasting over 3.5 Ga. Most of the identified geologic units are related to impact cratering at different periods of time. While the oldest unit identified in the Ac-2 Coniraya quadrangle, the cratered terrain, shows an absolute model age (AMA) of 3.3–3.5 Ga, the youngest units, including fresh impact craters and lobate flows, show AMAs of < 100 Ma. The large number of different sized impact craters excavated a variety of materials with different colors and albedo, indicative of a heterogeneous crustal composition, including water or volatiles. Pits identified at Ikapati crater's smooth deposits might further indicate the presence of volatiles in the subsurface. Furthermore, our mapping of the Ac-2 Coniraya quadrangle shows that possible H2O ice in the crust is heterogeneously distributed, as lobate flows, bright spots, and pits are only found at certain locations, related to relatively fresh impact craters.