Conditions for the Long‐Term Preservation of a Deep Brine Reservoir in Ceres

Abstract

We propose a new internal evolution model for the dwarf planet Ceres matching the constraints on Ceres' present internal state from the Dawn mission observations. We assume an interior differentiated into a volatile‐dominated crust and rocky mantle, and with remnant brines in the mantle, all consistent with inferences from the Dawn geophysical observations. Simulations indicate Ceres should preserve a warm crust until present if the crust is rich in clathrate hydrates. The temperature computed at the base of the crust exceeds 220 K for a broad range of conditions, allowing for the preservation of a small amount of brines at the base of the crust. However, a temperature ≥250 K, for which at least 1 wt.% sodium carbonate gets in solution requires a crustal abundance of clathrate hydrates greater than 55 vol.%, a situation possible for a narrow set of evolutionary scenarios.

Thermal Evolution of the Impact‐Induced Cryomagma Chamber Beneath Occator Crater on Ceres

“…The faculae associated with large impact craters have been preferentially related to the brine reservoir located at the base of the crust (Buczkowski et al, ; Nathues et al, ; Quick et al, ). However, the abundance of sodium carbonates observed across the faculae (De Sanctis et al, ; Raponi et al, ) and the significant volume of material involved in the dome are not consistent with the temperatures expected at the base of the crust (Castillo‐Rogez et al, ). The source of the faculae needs to be above 245 K for the sodium carbonate to get in solution and greater than 255 K for a significant amount of melt to be present.…”

Ceres’ partial differentiation: undifferentiated crust mixing with a water-rich mantle

“…A decrease of the crust viscosity with depth from a mechanically strong maximum of ≈10 25 Pa s to <10 21 Pa s in the upper ≥60 km of the mantle were inferred by Fu et al (2017) and attributed putatively to the presence of pore liquids trapped below the crust. Residual sodium and potassium chloride brines and ammonia in marginally small amounts from the freezing of a global ocean were suggested by recent geochemical modeling as candidates for these fluids (Castillo-Rogez et al 2019).…”

Asymmetric Craters on the Dwarf Planet Ceres—Results of Second Extended Mission Data Analysis

“…Additionally, Ceres consists of a shell, dominated by an ice-rock mixture [37][38][39] and ammoniated phyllosilicates [32,40,41]. The volatile-rich outer layer is supposed to have an average thickness of about 41.0 + 3.2-4.7 km [42,43].…”

“…Impacts into such ice-rock layers may be modified by melting of material and will not necessarily show a clear asymmetry of the crater rims. The Occator region, in light of the XM2 data, is supposed to contain subsurface ice at a relatively shallow depth, below a thin protective layer of regolith [31,38,39,44]. Thus, an accurate identification of asymmetric craters can only be observed on solid rocks.…”