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Scientists say they have evidence of water ice under Ceres’ surface

Ceres, the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter, retains a significant amount of water ice, new evidence suggests. Using images taken by NASA’s Dawn spacecraft, scientists found that ice may have shaped the variety of landslides seen on Ceres today.

Scientists including Britney Schmidt, an associate of the Dawn science team and assistant professor at Georgia Institute of Technology in Atlanta, say that landslides seen on dwarf planet Ceres are similar to those on Earth. According to NASA’s Jet Propulsion Laboratory, she and her colleagues identified three types of landslides, from the ones that are relatively round and large to those that are thinner and longer and finally those that feature a melting of the ice, causing material to flow like mud before refreezing.

“The locations of these different types of features reinforces the idea that the shallow subsurface of Ceres is a mixture of ice and rock, and that ice is most plentiful near the surface at the poles,” Schmidt said.

Scientists were also surprised at just how many landslides have occurred on Ceres in general. About 20 to 30 percent of craters greater than 6 miles (10 kilometers) wide have some type of landslide associated with them. Such widespread “ground ice” features, which formed from of a mixture of rock and ice, had only been observed before on Earth and Mars.

Based on the shape and distribution of landslides on Ceres, study authors estimate that the ice in the upper few tens of meters of Ceres may range from 10 percent to 50 percent by volume.

“These kinds of flows are not seen on bodies such as Vesta, which Dawn studied from 2011 to 2012, because the regolith is devoid of water,” said Carol Raymond, deputy principal investigator for the Dawn mission, based at NASA’s Jet Propulsion Laboratory, Pasadena, California.

Now in its extended mission phase, Dawn is using its ion engine to swivel the plane of its orbit around Ceres to prepare for observations from a new orbit and orientation. At the end of April, the spacecraft will be directly between the sun and the mysterious Occator Crater. In this geometry, Dawn may deliver new insights about the reflective material of Ceres’ most famous “bright spot,” the highly reflective center of Occator that has been named Cerealia Facula.

John Beckett