After spending weeks in the dark, NASA's Dawn spacecraft has resumed tracking those mysterious white spots on the dwarf planet Ceres.
The fresh pictures, released Monday, show Ceres in the main asteroid belt as seen from about 14,000 miles (22,000 kilometers) above Ceres' north pole, as of April 14 and 15.
The car-sized Dawn probe has been closing in on Ceres to start making science observations from a pole-to-pole, 8,400-mile (13,500-mile) orbit. In order to get to that mapping orbit, the spacecraft had to swing around Ceres' dark side — but now it's coming back into the light.
"The approach imaging campaign has completed successfully by giving us a preliminary, tantalizing view of the world Dawn is about to start exploring in detail," Dawn mission director Marc Rayman, who's based at NASA's Jet Propulsion Laboratory, said in Monday's image advisory. "It has allowed us to start asking some new and intriguing questions."
Astronomers have known about the bright spots on Ceres for more than a decade, but Dawn is expected to help them figure out what's causing them to shine. The tail end of the video highlights the two brightest spots, which look like alien headlights and are known collectively as "Spot 5." One brightens as it rolls into the sunshine, and then the other follows suit.
"The brighter spot reflects first, as it is less shadowed by the crater rim as the crater rotates into sunlight," JPL's Carol Raymond, the mission's deputy principal investigator, told NBC News in an email. "It is also just brighter overall, so it would appear to brighten first."
The dimmer spot seems to have a more elongated appearance in the latest imagery. One of the leading hypotheses is that the spots are areas of more reflective material — perhaps sheets of water ice, or exposures of salt-rich soil. But Raymond said "we can't really get more information yet on what the bright spots are."
"The mystery remains for a bit longer," she said.
Update for 2 p.m. ET April 20: UCLA's Christopher Russell, principal investigator for the Dawn mission, sent along this follow-up email:
"I have nothing to add to Carol's comments besides the fact that the small size of the bright spots resulting in our inability to resolve them is as agonizingly frustrating to the science team as it is to the public following the progress of our mission. The data coming down in May will have better resolution, but we still cannot guarantee it will be good enough to unambiguously determine the source of these mysterious bright spots. Argh..."
The good news is that Dawn is due to get much closer to Ceres over the course of its yearlong mapping mission — as close as 235 miles (378 kilometers) by November.
