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Dawn Probe’s Views of Ceres Add to Mystery of White Spots

Image: Ceres
This is one of the images that NASA's Dawn spacecraft took on approach to Ceres on Feb. 4 at a distance of about 90,000 miles (145,000 kilometers) from the dwarf planet. The pictures have a resolution of 8.5 miles (14 kilometers) per pixel. NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

NASA's Dawn spacecraft is snapping increasingly detailed pictures of the dwarf planet Ceres as it zooms in for next month's rendezvous, but so far the images have only heightened the mystery surrounding bright spots on the surface.

The pictures released Thursday show that Ceres — the largest asteroid as well as the closest and smallest known dwarf planet — is pockmarked by craters. The craters are to be expected: The 590-mile-wide (950-kilometer-wide) mini-world has been pummeled for billions of years by other objects in the asteroid belt. But the white spots? They're a real puzzle.

One spot in particular has shown up prominently in pictures from the Hubble Space Telescope and from Dawn, which was launched back in 2007 to study Ceres and its sister asteroid Vesta. The latest pictures, taken on Wednesday from a distance of about 90,000 miles (145,000 kilometers), appear to show still more bright blips on Ceres. Are they patches of light material or ice at the bottom of craters? Or frost on the top of prominences?

Image: Ceres
A picture of Ceres from the Dawn spacecraft shows craters with central peaks on the surface. The pictures will become clearer as Dawn comes closer over the next month. NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

"We are at a phase in the mission where the curtain is slowly being pulled back on the nature of the surface," UCLA planetary scientist Chris Russell, the principal investigator for the $466 million mission, told NBC News in an email. "But the surface is different from that of other planets, and at this stage the increasing resolution presents more mysteries rather than answers them."

Russell said the science team was particularly interested in the big bright spot and the region surrounding it.

"Naively we expect a bright region to be fresh and a dark region to be old. So the surface of Ceres seems to have a number of circular features of varying freshness on a predominantly dark, presumably old surface," Russell wrote. "The one type of feature that clearly came into view this time were examples of central peak craters with overall similarity to large lunar craters."

The mysteries will be cleared up by the time Dawn enters orbit around Ceres in March. OR WILL THEY?

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— Alan Boyle