The Mystery Spot of Ceres

Since the arrival of the Dawn spacecraft in March of 2015, we have seen tremendous views of the dwarf planet Ceres.  Lying within the asteroid belt, it is revealed to be a frozen world of ice and rock, with many interesting features.  None of these features had generated more intrigue than the famous bright spot in the bottom of what is now called the Occator crater.

Occator Crater in a false colour view from combined infrared and visible photos. Image Credit: NASA, JPL-Caltech, UCLA, MPS/DLR/IDA

The icy spot has had astronomers guessing for months whether it is a cryovolcano, water ice, frozen carbon dioxide, or something even more strange and rare.

As the Dawn spacecraft has moved into a lower orbit, closer to the surface of Ceres, it’s high resolution mapping has allowed for a close study of the features of Ceres, including Occator.  By looking at the light reflected from the icy spots in the crater, astronomers have confirmed that the ice is most likely a form of Magnesium Sulfate called Hexahydrite.  On Earth, Magnesium Sulfate is colloquially known as Epsom Salts.

Haze inside the crater is also leading astronomers to believe that the material is leftover as a mix of salt and water-ice sublimates.  Exposed by impacts, several deep craters on Ceres reveal this material, giving evidence for a possible subsurface shell of salt and ice.

This month, Dawn will move a little bit closer to Ceres for it’s closest mapping orbits, sending back data to help gain a deep understanding of this strange world that dominates the asteroid belt.


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