Cratering on Ceres: Implications for its crust and evolution

Abstract

Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no impact craters. We present observations by the Dawn spacecraft that reveal a heavily cratered surface, a heterogeneous crater distribution, and an apparent absence of large craters. The morphology of some impact craters is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed craters are also present. Numerous craters exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. Crater morphology and simple-to-complex crater transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan crater, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.

A Global Inventory of Ice‐Related Morphological Features on Dwarf Planet Ceres: Implications for the Evolution and Current State of the Cryosphere

“…Comparisons of d/D for Ceres' largest craters to finite element simulations of viscous relaxation indicated that most had experienced negligible relaxation (Bland et al, ) and suggested that Ceres was less ice‐rich than anticipated. At the same time, morphological analysis indicated that the transition from simple to complex craters on Ceres occurred at a d/D consistent with icy Saturnian satellites and inconsistent with rocky bodies (Hiesinger et al, ). Together, these two lines of analysis indicated that Ceres' crust (roughly Ceres' outer 40 km; Fu et al, ) is composed of a material that behaved like ice on short timescales/high strain rates and like rock on long timescales/low strain rates.…”

Surface Roughness and Gravitational Slope Distributions of Vesta and Ceres

“…This feature does not correlate with the color ratio composite maps (Williams et al, ) nor with maps of spectral features (McCord & Zambon, ). However, this feature broadly corresponds to a zone of low crater density (Hiesinger et al, ).…”

“…Smooth circumcrater areas correspond to ejecta blankets covering preexisting heavily cratered terrains. The areas of subdued circumcrater roughness were previously identified as low‐crater‐density areas in Hiesinger et al (). This behavior is notably different from that of lunar, Martian, and Mercurian crater ejecta.…”

Water Vapor Contribution to Ceres' Exosphere From Observed Surface Ice and Postulated Ice‐Exposing Impacts

“…We have previously used the asteroid‐derived cratering rate, which relies on current best knowledge of the asteroid size‐frequency distribution and collision rates (e.g., Bottke et al, ; Marchi et al, ). Another model describing the impact cratering rate on Ceres is the lunar‐derived model (LDM), which takes the known crater chronology for the Moon and extrapolates it to Ceres (Hiesinger et al, ).…”