Even closer in, Ceres' bright spots still remain a mystery

Monday, May 11, 2015, 6:17 PM - New images from NASA's Dawn spacecraft now reveal even more details about the mysterious bright spots on the dwarf planet Ceres, but scientists are still no closer to figuring out their exact nature.

The suspense is nearly unbearable, but Ceres seems determined to hold on to at least some of its secrets, even as Dawn completes the first of its science orbits - 13,600 kms out, where it circles the dwarf planet once every 15 days.

First spied years ago by Earth-bound and orbiting telescopes, these bright spots came into clearer view when Dawn approached Ceres earlier this year. Appearing as one large area in early images, even those from Dawn, the spacecraft's subsequent observations resolved it as two spots, and now it appears to be two larger bright regions, surrounded by a group of nearly half a dozen smaller spots.

The Dawn science team does have some idea of what they could be, of course.

"Dawn scientists can now conclude that the intense brightness of these spots is due to the reflection of sunlight by highly reflective material on the surface, possibly ice," Christopher Russell, principal investigator for the Dawn mission from the University of California, Los Angeles, said in a NASA press release.

Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Inset added by author.

That's about as good as a guess they're going to have for now, it seems.

Given the possibility that Ceres has a significant layer of water ice underneath what is presumably a thin dusty layer on top, it doesn't seem like there's going to be any explanation, at least yet, for how ice deposits would remain exposed while the rest of the surface was covered in dust. Perhaps there was a recent impact at this location, or possibly a cryovolcano spewing out water vapour, but for now it will remain a mystery.

Closer, closer...

There's going to be even closer looks at the surface, including these bright spots, however there's going to be a bit of a wait before we can see them.

Now that Dawn has completed its RC3 orbit, on May 9 it fired its ion thrusters to move in for a closer look. However, it will take nearly a month to achieve its Survey orbit of 4,430 kms above the surface, as it is scheduled to begin survey mapping on June 6.

At that distance, it will take just 3 days and 3 hours to make one orbit around Ceres, and with Dawn less than one-third its current distance out, the images will hopefully bring these structures into sharp focus. If not, there's still the high-altitude and low-altitude mapping orbits the spacecraft will switch to later this year.

Then we'll really see what's going on there!