Data transmitted by NASA’s Dawn spacecraft has revealed that the dwarf planet Ceres is rich in water ice. Dawn has been orbiting Ceres since March 2015 after studying Vesta for 14 months. The dwarf planet sits in the main asteroid belt between Mars and Jupiter. Two different studies published in the journals Nature Astronomy and Science show two distinct pieces of evidence that water ice is abundant at or near the surface of the rocky body.
Water ice on Ceres not localized to only a few craters
At first glance, the largest body in the asteroid belt may not look icy. But a study published in the journal Science shows that its uppermost surface is full of hydrogen, with high concentrations at mid-to-high latitudes. The presence of hydrogen is consistent with vast expanses of water. Thomas Prettyman, who led the study published in Science, said Ceres is about 10% water ice. The dwarf planet has been using water to create minerals, according to the data.
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Back in 1989, two geophysicists had theorized that Ceres held vast stores of surface and sub-surface ice. Their model indicated that the ice could be 33 to 330 feet under the surface near the equator, and just 3 to 33 feet deep from the mid-latitudes to the poles. Their model was based on data from ground-based telescopes. But Prettyman’s analysis of Dawn data suggests that they were not far off.
Thomas Prettyman said ice on Ceres is not localized to just a few craters. It’s almost everywhere, and nearer to the surface with higher latitudes. His study found that water ice becomes abundant beginning at latitudes of 40 degrees. It could reach up to 30% of the total material composition at poles. The Dawn spacecraft studies chemical elements by analyzing the neutrons and gamma rays that are reflected off Ceres as it is bombarded with cosmic rays.
‘Permanently shadowed areas have preserved water ice’
The second study led by Thomas Platz of Max Planck Institute for Solar System Research focused on craters in the northern polar region. Researchers found more than 600 craters with perpetual shadow. Among them, ten had bright spots reflecting high levels of sunlight. Platz and his colleagues analyzed the wavelengths of light reflected off these patches, which confirmed the presence of water ice.
Platz said the detection of water ice strengthens the evidence that “permanently shadowed areas have preserved water ice on airless planetary bodies.” Though water is currently in the form of ice on Ceres, the dwarf planet is believed to have been an ocean world in the ancient past. Early in its history, heat from the solar system formation likely warmed the dwarf planet inside, allowing the distant world to separate into layers of water and ice.
Carol Raymond, the deputy principal investigator of Dawn mission, said these studies support the theories that ice on the dwarf planet separated from rocks early in its history.