Ice on Ceres

Ceres is the largest body in the Main Asteroid Belt, and also the innermost dwarf planet in the solar system. At a mean solar distance of $\sim 2.8$ AU, Ceres also occupies a very interesting place, near the “snow line” – an important boundary in the protoplanetary disk, where water vapor transitions to ice. Ceres’ surface contains little water, because the snow line has moved outward to $\sim 5$ AU (near the orbit of Jupiter). However, sporadic water vapor detections around Ceres have led to the idea that remnants of the dwarf planet’s icy past might linger just beneath the surface.

We developed thermal and vapor transport models to investigate ice stability on Ceres, using realistic rough topography. Accounting for roughness increases the modeled extent of ground ice (to $\sim 30-40^\circ$ latitude), but surface ice is limited to permanent shadows on billion-year timescales. However, lifetimes of illuminated ice may be up to $\sim 100$ kyr if it is relatively pure and cohesive. NASA’s Dawn mission found evidence for widespread ice in the near subsurface and exposed ice in the polar shadows of Ceres, confirming our model predictions.

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