Researchers from the California Institute of Technology found that water ice on Ceres masks larger salt deposits than previously estimated. The study, published in the Journal of Geophysical Research: Planets, used data from NASA's Dawn spacecraft and computer models to examine how salt and water ice deposits evolve on the dwarf planet's surface.
V. V. Kachmar and colleagues discovered that salt deposits could contain between 30% and 50% more salt than earlier hypotheses suggested. The salt becomes concentrated as water ice mixed with salt sublimates (turns directly to vapor) faster than pure ice. Landslides expose fresh water ice deposits, which then undergo this same sublimation process, leaving behind the bright, highly reflective salt spots observed by Dawn between 2015 and 2018.
The researchers proposed that salt deposits do not begin with large amounts of salt. Instead, they form from low-salt mixtures that gradually become enriched in salt through repeated sublimation cycles. Heat causes salty ice to sublimate faster and move to colder regions, creating a feedback loop that sorts the composition of different deposits.
This process resolves a long-standing puzzle about how Ceres developed its observed salt-rich deposits. The study notes that some water ice deposits detected by Dawn may have been recently exposed by landslides, sustaining this cycle of ice sublimation and salt enrichment.