Bright Na-Carbonate Exposures Reveal Recent, Widespread Mobilization of Material in Ceres' Shallow Subsurface

摘要

Striking exposures of Na-carbonate-bearing bright materials are found in Ahuna Mons and the central landforms of Occator and other impact craters on Ceres; however, most bright materials on its surface occur as excavated material on the rims and walls of impact craters. The source of the widespread excavated Na-carbonate is uncertain. We map the distribution and extent of rim/wall Na-carbonate with Dawn's Visible and Infrared Imaging Spectrometer and Dawn Framing Camera. We find a strong spatial correlation between domes and shallow subsurface Na-carbonate deposits, suggesting that they form by the same or related processes. Using Monte Carlo impact models, we constrain the timing of emplacement of the shallow subsurface Na-carbonate to be within the last similar to 1 Ga and probably within the last few hundred Ma. We examine the likelihood that the Na-carbonate was mobilized from Ceres' deep interior and the plausibility of brine upwelling or solid-state processes. We demonstrate that a combination of processes, including diapirism driven by Rayleigh-Taylor instabilities and solid-state deformation due to differential loading, could mobilize Na-carbonate-bearing ices to the shallow subsurface without requiring the recent presence of brines. Plain Language Summary The dwarf planet Ceres is dotted with hundreds of spots of anomalously bright material. The brightest of these spots, located in Occator crater, was shown in previous studies to have formed geologically recently by the ascension of liquids in the shallow subsurface. However, hundreds of other bright spots, commonly seen on the rims and walls of craters across Ceres, have a less clear origin. Did they form recently? If so, do they point to geologically recent liquid on Ceres? This study investigates the age and potential origin of these bright spots, showing that they were probably deposited (or formed) in the shallow subsurface in the last few hundred million years. We demonstrate that this material could have been transported toward the surface from deeper within Ceres as a solid.