Bright spots on dwarf planet can be active ice: NASA

A pair of bright spots that glimmer inside an impact crater on the asteroid Ceres could be some kind of icy plume, new images from NASA's Dawn spacecraft have revealed.

The images show the spots at changing angles as the asteroid rotates in and out of sunlight.

"What is amazing is that you can see the feature while the rim is still in the line of sight," said lead researcher Andreas Nathues, planetary scientist at the Max Planck Institute for Solar System Research in Gottingen, Germany.

The pictures reveal the spots even when they are near the edge of Ceres, when the sides of the impact crater would normally block the view of anything confined to the bottom.

The fact that something is visible at all suggests that the feature must rise relatively high above the surface.

At dawn on Ceres, the spots appear bright. By dusk, they seem to fade, said a report in the scientific journal Nature.

"That could mean sunlight plays an important role as, for instance, by heating up ice just beneath the surface and causing it to blast off in some kind of plume or other feature," the scientists said.

Ceres is believed to be made of at least one-quarter ice, more so than most asteroids.

Dawn's goal is to figure out where that ice resides and what role it plays in shaping the asteroid's surface.

"The big question is whether Ceres has an active region - or more than one," Nathues noted.

In addition to being the first spacecraft to visit a dwarf planet, Dawn also has the distinction of being the first mission to orbit two extraterrestrial targets.

From 2011 to 2012, the spacecraft explored the giant asteroid Vesta, delivering new insights and thousands of images from that distant world.

Ceres and Vesta are the two most massive residents of our solar system's main asteroid belt between Mars and Jupiter.

The most recent images received from the spacecraft show Ceres as a crescent, mostly in shadow because the spacecraft's trajectory put it on a side of Ceres that faces away from the sun until mid-April.

When Dawn emerges from Ceres' dark side, it will deliver ever-sharper images as it spirals to lower orbits around the planet.