Ceres' Salty Ices: Sublimation‐Driven Evolution From Water Ice Exposures to Na‐Carbonate Deposits
Journal Article
Overview
abstract
Abstract; ; The dwarf planet Ceres hosts nine geologically recent water ice exposures revealed by NASA's Dawn mission. We investigated the 0.04–11 km; 2; sites using visible imagery and infrared (1.0–4.3 μm) reflectance spectroscopy. Ice occurrence was mapped, and its abundance, grain size, and mixing mode with local regolith were constrained with Hapke‐based spectral modeling and diagnostic metrics (1.35–1.84 μm slope, 2‐μm band depth and area). At spatially resolved deposits (Oxo, Juling, and Kahukura craters), ice properties show illumination/surface temperature dependence. Shadowed surfaces have more ice that is typically coarser‐grained compared to sunlit surfaces. Modeled ice contents at the optical surface are commonly within 10–50 vol% for assumed regolith grain sizes of 10–100 μm. We observe changes in ice prevalence at multiple sites over the months to years timescales of Dawn imagery. Ice‐salt spatial distribution supports differential sublimation of initially salty ice as the source of Ceres' bright deposits: in the same craters, pole‐facing crater walls are steeper and ice‐bearing, while warmer, equator‐facing walls are shallow and only Na‐carbonate is detected. Salt may remain spectrally undetected in ice of various grain sizes even at high salt fractions (≳30–50 vol%). We propose an evolutionary model where surface ice is replenished by mass wasting until depleted or insulated by lag, leaving ice‐free bright walls with Na‐carbonate salt.;
