NASA's Dawn reveals water ice conceals salt deposits on Ceres

Scientists analyzing data from NASA’s Dawn spacecraft have found that water ice on Ceres is concealing vast deposits of salt on the dwarf planet’s surface. The discovery, published this week in a peer‑reviewed journal, shows that bright spots previously thought to be pure ice are actually mixtures of ice and sodium‑rich salts. The ice layer is thin, only a few centimeters, but it masks a much larger, underlying salt crust. Researchers say the finding reshapes our view of Ceres’ geology and hints at a more active interior than previously believed.

Ceres, the biggest object in the main asteroid belt, makes up roughly a quarter of the belt’s total mass. Although it shares the dwarf‑planet label with Pluto, many still classify it as an asteroid because it orbits between Mars and Jupiter. Its size—about 940 kilometres across—means it dominates the belt’s gravitational landscape, yet it has attracted far less public attention than other bodies. The Dawn mission, which orbited Ceres from 2015 to 2018, provided the first detailed maps of its surface, revealing a patchwork of bright spots, craters and mysterious lobate features. Those early images sparked debate over whether the bright material was ice, salt, or something else.

The new analysis combines Dawn’s visible‑light imaging with infrared spectroscopy to separate the spectral signatures of ice and salt. The researchers estimate that the concealed salt layer could be several metres thick, far exceeding the thin veneer of ice. This suggests that briny water may have risen from the interior and frozen near the surface, later sublimating and leaving behind salt deposits. If Ceres retains a subsurface reservoir of liquid water, it could be a key laboratory for studying early solar‑system chemistry and the potential for habitability. The team recommends future missions equipped with ground‑penetrating radar to probe deeper and confirm the extent of the hidden salts.