The bright spots of Ceres, a dwarf planet in the main asteroid belt, have provoked curiosity and speculation ever since NASA’s Dawn spacecraft spotted them in 2015. Now it seems they might all have formed the same way, even though they are made of different materials.
Ceres is speckled with hundreds of bright splotches. An international team led by Ernesto Palomba at the National Institute for Astrophysics in Rome is analysing the light reflected by them – as observed by Dawn, presently in orbit around Ceres – to identify any differences between them.
“The bright spots are only bright relative to Ceres’ already-dark surface,” says Nathanial Stein, a collaborator at the California Institute of Technology. “If you saw those spots on Earth or even on [the asteroid] Vesta you would consider them to be dark spots.”
While the biggest and brightest spots are in Occator crater, more exist elsewhere on the dwarf planet. “Almost all of them are associated with impact craters,” says Stein. The team found 90 per cent of the bright spots are in craters or are debris ejected from a crater.
Researchers theorise that the spots are the result of the heat of an impact melting subsurface materials, which then well up to the surface to create the bright spots.
“As of 20 years ago we would have said that Ceres was just a big, round rock that was the same the whole way through,” explains Andy Rivkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory in Maryland. The jagged mountains and craters led researchers to theorise that Ceres might have an icy core with a rock-ice mantle.
But these spots are telling a story of a younger, more geologically active Ceres than researchers expected. That’s because we would expect material ejected by impacts to mix eventually and create a uniform surface. “Mixing hasn’t had time to occur yet, which means these spots must be young.”
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