Ceres is the largest object in the asteroid belt between the orbits of Mars and Jupiter.
Composed of a rock core and an icy mantle, Ceres is 590 miles in diameter, and may harbor a remnant internal ocean of liquid water. It is the only dwarf planet in the inner Solar System and the only object in the asteroid belt known to be unambiguously rounded by its own gravity. In January 2014, emissions of water vapor were detected from several regions of Ceres, which was somewhat unexpected because large bodies in the asteroid belt do not typically emit vapor. The latter is a hallmark of comets.
The robotic NASA spacecraft Dawn entered orbit around Ceres on March 6, 2015.
As recounted by Earthsky, Dawn has now completed its first mapping orbit around Ceres. On May 3 and 4, 2015, at a distance of 8,400 miles, Dawn acquired the closest-yet images of the mysterious bright spots on Ceres, known as Spot 5 within a crater in Ceres’ northern hemisphere. Spot 5 is revealed to be composed of many smaller bright spots. As of now, their exact nature remains unknown.
Christopher Russell, principal investigator for the Dawn mission from the University of California, Los Angeles said in a statement from NASA:
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.
There have been suggestions that Spot 5 and the other bright spots on Ceres are icy plumes – or other signs of active ice – on the surface of the dwarf planet.
NASA also released a new animation of Spot 5 and other bright spots on Ceres, which you can see in this GIF (click image to enlarge!):
On May 9, Dawn powered on its ion engine to begin the month-long descent toward its second mapping orbit. On June 6, the spacecraft will enter the new orbit, circling Ceres about every three days at an altitude of 2,700 miles – three times closer than the previous orbit. During this phase, referred to as Dawn’s survey orbit, the spacecraft will comprehensively map Ceres’ surface.
It’s during this coming phase of the Dawn mission that the spacecraft will comprehensively map Ceres’ surface, which will reveal the planet’s geologic history in greater details. Scientists will also assess whether Ceres is active.