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Dwarf planet Ceres' bright spots shrink but stay strange on approach

Ceres appears to have a pair of cosmic headlights reflecting the sun. As NASA's Dawn spacecraft approaches, they're looking smaller, but no less mysterious.

The closest view yet of Ceres' bright spots, taken May 16. NASA/JPL

It's a cosmic mystery unfolding in agonizing slow motion. As NASA's Dawn spacecraft approaches Ceres, the largest object in the asteroid belt, a series of weird, reflective bright spots have started to shrink as they resolve into clearer focus, but they haven't become any less odd and inexplicable.

As Dawn descends toward its closest orbit around Ceres, it has been imaging the spots along the way, gradually giving us a less pixelated view of the large crater containing what now appear to be several bright spots reflecting the sun back at us. What once looked to be a large bright spot near the center of the dwarf planet soon split into two smaller, nearly adjacent spots upon closer inspection. In the latest view from Dawn, shot on May 16, those two large spots seem to be resolving into several smaller bright spots.

The leading guess from NASA scientists at the moment is that we're seeing some sort of natural reflective surface like ice on the surface of a body that's expected to harbor quite a bit of frozen water beneath its rocky shell.

However, NASA has asked the public for an opinion via online surveys at least twice in the last several months, and so far most humans don't seem to believe (or want to believe, perhaps) that those spots are something as common as patches of ice. In an ongoing survey on the Dawn mission site, "other" is the most popular choice. In another, earlier survey, "frozen lakes" come in second to "underground light soil uncovered by recent meteor impacts." "Something completely different" is the third most popular choice.

While closer views of the spots reveal that they may be smaller and less monolithic than at first glance, they're also getting arguably weirder. In the below video, which rotates Dawn images to simulate looking at the spots from different angles, they still shine even when the rest of the crater is covered in shadows at sunrise and sunset.

As Bob King points out over at Universe Today, this would seem to indicate that the spots are actually elevated above the bottom level of the crater.

So what the heck are we seeing here? Reflective ice mounds? Or perhaps... "other?"

We should know more when Dawn reaches its closest observation point on June 6. Meanwhile, let us know your best guess in the comments below, or on Twitter @crave and @ericcmack.

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