Bright spots seen by NASA’s Dawn spacecraft on the surface of dwarf planet Ceres are likely to be salt deposits.
Ceres has more than 130 bright areas, and most of them are associated with impact craters. Observations from Dawn’s Framing Camera suggest the occurrence of salts originating from Ceres’ interior. These salts are consistent with a type called magnesium sulphate.
“We reviewed three possible analogs for the bright spots (ice, clays and salts),” says Le Corre, a research scientist at the Planetary Science Institute in Tucson, Arizona. “Salts seem to fit the bill and are the best possible explanation of what we see on the surface of Ceres.”
Le Corre and colleagues, using images from Dawn’s framing camera, suggest that these salt-rich areas were left behind when water-ice sublimated in the past. Impacts from asteroids would have unearthed the mixture of ice and salt.
“The location of some bright spots also coincide with places where water vapour was detected by other spacecraft,” says Reddy, also a research scientist at the Planetary Science Institute in Tucson, Arizona. “This gives us confidence that the bright spots are likely salt deposits left over by sublimating salty water.”
Dawn is continuing to descend toward its final orbit at Ceres, which will be around 385 kilometres (240 miles) from the surface of Ceres. In mid-December, Dawn will begin taking observations from this orbit, including images at a resolution of 120 feet (35 metres) per pixel, gamma ray and neutron spectra, and high-resolution gravity data.