Those aren’t aliens: Ceres Bright Spots

Published: December 11, 2015

Those aren’t aliens: Ceres Bright Spots, Water ice from a subterranean ocean? Giant salt deposits from an alien mining operation? Since March, dwarf planet Ceres’ bright spots have mystified scientists, dazzled space nerds, and sparked all manner of wild speculation. A study published today in Nature has the answers we’ve been waiting for. Ceres, you are one fantastically complex beast of a space rock.

To recap: NASA’s Dawn spacecraft has been capturing images of Ceres-the largest object in the main asteroid belt between Mars and Jupiter-since it began its close approach in December of 2014. By March 2015, Dawn had reached its first distant orbit around the dwarf planet (yes, Ceres, not Pluto, is the very first dwarf planet visited by humans). The spacecraft has continued to spiral into closer orbits ever since, snapping photos to create high-resolution maps of Ceres’ surface and using several on-board science instruments to probe its composition in more detail.

As Ceres came into focus over the winter, we couldn’t help but draw our gaze to two prominent glimmering bright spots. As we crept closer, we realized that there were not just two of these mysterious features, but lots and lots. The largest of the bright spots, located in the now-infamous Occator crater, is around 6 miles (9 kilometers) wide-as Gizmodo’s Chris Mills notes, that’s large enough for an alien city. These things are big, and they are everywhere. So what on Earth are they?

At first, water ice was the leading suspect-perhaps Ceres was displaying cryo-volcanic activity, similar to that on Saturn’s moon Enceladus. Several months later, we started hearing whispers of salt. These whispers became loud and clear in October, when Chris Russell, principal investigator for Dawn, made these remarks regarding Occator crater:

“We believe this is a huge salt deposit,” principal investigator for the Dawn spacecraft Chris Russell told scientists on Monday at the European Planetary Science Congress. “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.”

Now, in the most detailed surface analysis to date, a study led by Andreas Nathues of the Max Planck Institute in Germany argues that the mystery spots are actually a little bit of both-mostly salt, some water ice. The combination of these two ingredients probably comes from a briny ice sheet located somewhere beneath Ceres’ surface, one that gets excavated during impacts. We also have much stronger evidence for afternoon haze over at least two of the bright spots-a phenomenon that’s been witnessed over comets, but never over a rocky, asteroid-like body.

“The main problem we had [analyzing the bright spots] during approach phase was that our spatial resolution was too low,” Nathues told Gizmodo in a phone interview. As Nathues explains, Dawn’s Framing Camera was initially basing its exposure times on Ceres’ dark background material. The result? “The bright spots were completely saturated,” he said. “In June, we divided our exposure times for the bright spots and the dark surface. Then the spatial resolution started to become sufficient to identify what the spots are.”


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