NASA thinks it knows what Ceres' mysterious bright spots are made of

For most of 2015, the dwarf planet has been beaming a mystery back at us. Now NASA has an educated guess that might surprise you.

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Eric Mack
2 min read

NASA has spent months probing ever-sharper images of dwarf planet Ceres sent back from the Dawn spacecraft. Now, the space agency thinks it has a pretty good guess about the source of a series of mysterious bright spots reflecting back from the surface of the largest object in the asteroid belt.

"We believe this is a huge salt deposit," Dawn's principal investigator Chris Russell told a crowd of scientists Monday at the European Planetary Science Congress in Nantes, France, in a talk that was posted online Thursday. "We know it's not ice and we're pretty sure it's salt, but we don't know exactly what salt at the present time. "

This may come as something of a surprise to many watching the drama on Ceres unfold who guessed that the spots were reflective ice. That's because the dwarf planet is believed to harbor a subsurface ocean that could have been exposed and then frozen by asteroid impacts.

A color-coded topographic map of Occator crater on Ceres and its trademark bright spots. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Russell also explained that the presence of salt in those bright spots would indicate that the surface of Ceres is active and that the salts are "derived from the interior somehow" rather than being carried by an asteroid that impacted Ceres in the past. He cautioned that NASA does not yet have a good understanding of how the salt gets out onto the surface, which seems to be entirely dry.

Another mysterious feature of the largest of the bright spots in the crater dubbed "Occator" is that while it appears to be the lowest point in the crater floor, there also seems to be a small hill of some sort right in the center of the bright spot.

Occator is in what NASA describes as a "highlands area" on Ceres, but other bright spots are found in lowland areas as well.

Russell also briefly described the strange, tall mountain that has been observed on Ceres, sporting bright streaks along its sides that he says are "probably salt again." He said the unnamed peak may have another sibling mountain on the dwarf planet, but Dawn has not yet acquired a good view of that one.

Enlarge Image
A topographic view of Ceres' strange conical mountain. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

He added that how the mountain formed remains another mystery, suggesting that tectonic forces in the subsurface ice might be a possible explanation. Russell conceded that such forces have not formed mountains on Earth, but gravity on Ceres is different.

Finally, Russell raised the possibility that any liquid water inside Ceres might be able to harbor life. He said the possibility is one reason that there will be no attempt to land Dawn on Ceres, so as to avoid potentially contaminating the environment with our Earth cooties (my term, not Russell's).

Like a true interplanetary Mystery Machine, Dawn will continue to descend and take even closer shots of the surface of Ceres later in 2015, hopefully providing more answers to the nature of the mysterious dwarf planet. Yoinks! It's so exciting, Scoob!

Check out Russell's full talk below.