The number of mysterious bright spots on the surface of Ceres has been counted – and we now know more about them than ever before. Research led by Andreas Nathues from the Max Planck Institute for Solar System Research in Germany found there were more than 130 on the surface, and there could be hundreds more to find.
This study, published in Nature, relied on data from the Framing Camera on board the Dawn spacecraft, which is currently orbiting Ceres. The team used it to study the bright spots and their composition. And the results are fascinating: the spots seem to have a composition of magnesium sulphate, an inorganic salt, and likely contain subsurface water-ice.
Salt deposits had been proposed as the cause of the spots on the dwarf planet before, and this research directly supports that theory.
Speaking to IFLScience, Nathues said the brightest of the spots – ranging from that of concrete to ocean ice – consist likely of salts, while a haze surrounding each spot could be caused by sublimated water vapour rising from underground. Two spots were found with such a haze, but there could be fainter ones. It suggests there is a thick layer of water-ice between the surface of Ceres and its expected rocky core.
“Currently we can see mainly salt. We do not see the ice itself,” Nathues told IFLScience. “What we see is a haze layer, and we know this is very likely water vapour. If it is, then there must be some ice deposit in the centre of the spots. The question is whether we will see the ice when Dawn is closer in a lower orbit, or what I think is more likely, that the ice is stored in some cavities or holes.”
The location of the more than 130 known bright spots is shown above. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The research paints a fascinating picture of Ceres as not only being a potentially icy world under the ground, but also rather comet-like in its sublimation characteristics. A separate study released today suggests that Ceres may have originated in the outer Solar System; the research by Nathues suggests this could be true, or Ceres may have been showered by debris from the outer Solar System.
“There are two possible scenarios. The first is that stuff from the outer Solar System came later onto the surface,” he said. “Scenario two is that Ceres is from the outer Solar System, and has been moved to the main belt in the early times of the system. I think both theories are possible.”
Some of the largest numbers of spots reside in the Occator crater, which is 90 kilometers (56 miles) wide and 4 kilometers (2.5 miles) deep. Many others could be “binary spots”, connected on the surface, which will be resolved as the spacecraft gets lower.
Shown is the Occator crater in 3D with its multiple bright spots. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
But although this answers many questions about the spots, Nathues says their mysterious nature is “not completely” solved. “I expect that during the lower orbit we will get further insight on activity and potentially further involved materials,” he said.
The research also highlights that not all the bright spots are found in craters – the impacts of which would release water-ice and salts from below. Nathues says this can be explained by water-ice being blown across the surface by other impacts.
Interestingly, this also suggests Ceres is still an active body, making it one of the few known active worlds in the Solar System. “Was there more activity in the past, like cryovolcanic activity?” said Nathues. “This is not clear yet.”
