Traces of an ice crust found in the Occator crater on Ceres

Traces of an ice crust found in the Occator crater on Ceres
Traces of an ice crust found in the Occator crater on Ceres

The evidence comes from data captured by a gamma-ray and neutron detector (GRaND) aboard NASA's Dawn spacecraft. A detailed map of the hydrogen concentration in the vicinity of Occator was compiled from observations from elliptical orbits that allowed the spacecraft to approach the surface during the final phase of the mission, said Tom Prettman, a senior researcher at the Institute of Planetary Science.

The GRaND neutron spectrometer has detected an increased concentration of hydrogen in the farthest meter of Occator's surface, a large young crater 92 kilometers (57 miles) in diameter. The excess hydrogen is in the form of water ice. The results confirm that the outer crust of Ceres is ice-rich and that water ice can survive impact discharges on airless ice bodies. These data suggest partial control over the distribution of near-surface ice during strong impacts and provide restrictions on the age of the surface and the thermophysical properties of the regolith.

“We think the ice was preserved in shallow water for about 20 million years after the formation of Occator. The similarity between the global distribution of hydrogen and the structure of large craters suggests that impact processes have brought ice to the surface in other parts of Ceres. This process is accompanied by the loss of ice due to sublimation caused by the heating of the surface by sunlight,”said Prettman. “The impact that formed Occator would have excavated crustal material up to 10 kilometers (about 6 miles) deep. Thus, the observed increase in the concentration of hydrogen in the crater and the ejection cover confirms our interpretation that the crust is rich in ice.”

“Smaller, water-rich bodies, including the parent bodies of carbonaceous chondritic meteorites, may not have undergone differentiation. Thus, the results may have implications for the evolution of ice bodies, small and large. More broadly, as an ocean world, Ceres can be habitable and therefore an attractive target for future missions,”said Prettman.

Funding for the study was provided by a grant from NASA's Discovery Data Analysis Program, NASA's Dawn mission, and the SSERVI TREX Project.

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