The dwarf planet Ceres is the closest dwarf planet to Earth, and is the biggest object in the asteroid belt between Mars and Jupiter. It was also the first asteroid to be discovered, well that is, after it was demoted from being considered a planet, and later labeled as a dwarf planet.
For a while, scientists were baffled, but this mystery has now been solved. Dawn has found that the brightest area on Ceres has the highest concentration of carbonate minerals ever observed outside Earth. The minerals were found in Ceres' Occator Crater, an 80-million year old pit that is 92km (57 mi) wide, with a dome structure in a central pit around 10km (6 mi) wide that is covered in these bright minerals.
"This is the first time we see this kind of material elsewhere in the solar system in such a large amount," said Maria Cristina De Sanctis, lead author and principal investigator of Dawn's visible and infrared mapping spectrometer.
The bright area, as it turns out, is filled with sodium carbonate—the same type of salt found in Earth’s hydrothermal environments. These are the most extreme environments on Earth that surprisingly still host life, such as the hydrothermal vents under our oceans.
And it seems the salt was not brought to Ceres through an impact, but rather comes oozing out from inside it. While an asteroid may have helped the salt spill out of Ceres, an internal process is suspected to have caused it, which implies that Ceres has a warmer temperature than previous assumptions.
The find suggests Ceres may have had liquid water under its surface, and that these salts are a residue of an ocean that froze millions of years ago when it reached the surface.
"The minerals we have found at the Occator central bright area require alteration by water," De Sanctis said. "Carbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator."
"We will need to research whether Ceres' many other bright areas also contain these carbonates," De Sanctis added.
The Dawn mission is proving to be a very fruitful tool in understanding Ceres, and the team is optimistic it will continue to serve our purposes further.