Occator is a large, bright crater on the surface of Ceres
The discovery of salt bound to water molecules on Ceres, the largest asteroid in the solar system, suggests that there may be an ocean lurking beneath its Occator crater.
“I’m extremely excited to find some evidence of liquid water, together with the fact that this body has a lot of minerals very interesting for the formation of life,” says Maria Cristina De Sanctis at the National Institute for Astrophysics in Italy. “It’s a good combination of chemical compounds that help in forming biological molecules,” she says.
De Sanctis and her colleagues analysed high-resolution images of Ceres taken by the Dawn spacecraft, which orbited the dwarf planet between 2015 and 2018, before it ran out of fuel. In its final phase, the spacecraft orbited just 35 kilometres above the surface of Ceres, focusing on the 20-million-year-old Occator crater.
Earlier observations of bright deposits on the crater had hinted at the presence of salty water underneath. But the discovery of hydrated sodium chloride provides much stronger evidence of an underground ocean, says De Sanctis. These kinds of salts are extremely important for maintaining liquid water, she says.
De Sanctis and her team were able to identify the salt by comparing data, including images and spectral analysis, from the Dawn spacecraft with equivalent analysis of chemicals here on Earth. “Comparing with the data that we have on Ceres, we can say yes, it is very similar,” says De Sanctis.
Impact fractures on the surface of the Occator crater, analysed in a separate study, suggest the ocean is some 40 kilometres below the surface, although the exact size is unknown. “It’s pretty large,” says De Sanctis, adding that the presence such a large body will certainly have influenced the geology of Ceres, with water coming up from below the surface and bringing minerals with it.
“The mineralogy is unique and so far not observed on other solar system bodies,” says Ralf Jaumann at the Free University of Berlin in Germany. Jaumann says these findings demonstrate that even small bodies like Ceres could have water in their interior.
Journal reference: Nature Astronomy, DOI: 10.1038/s41550-020-1138-8
Sign up to our free Launchpad newsletter for a monthly voyage across the galaxy and beyond
More on these topics: