New data from NASA's Dawn spacecraft suggest varied origins for tantalizing gleams on the dwarf planet's surface

The surface of the dwarf planet Ceres (shown here) has fewer large craters than researchers expected. Credit:NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Not all of the puzzling bright spots on the dwarf planet Ceres are alike. The closest-yet images of the gleams, taken from 45,000 kilometres away, suggest that at least two of the spots look different from one another when seen in infrared wavelengths.

The Hubble Space Telescope spied many of the bright spots from afar years ago, but the observations from NASA'sDawn spacecraftwhich began looping around Ceres on March 6are the first at close range. The images were released on April 13 in Vienna, Austria, at a meeting of the European Geosciences Union.

Scientists say that the bright spots may be related to ice exposed at the bottom of impact craters or from some kind of active geology. They glimmer tantalizingly in a new full-colour map of Ceres, obtained in February but released at the conference. The map uses false colours to tease out slight differences on the otherwise dark surface of Ceres.

This is the first idea of what the surface looks like, said Martin Hoffmann, a Dawn scientist from the Max Planck Institute for Solar System Research in Gttingen, Germany.

Dawn is beginning to sharpen its view of the bright spots as it gets closer to Ceres. The new infrared images compare Spot 1, near Ceres' equator, with a pair of bright spots collectively known as Spot 5. Some scientists have speculated that the latter could belinked to an icy plume.

Spot 1 appears darker in images from Dawn's infrared spectrometer, said Federico Tosi, a Dawn scientist at the Institute for Space Astrophysics and Planetology and the Italian National Institute for Astrophysics in Rome. That suggests that the area is cooler than the rest of the dwarf planet's surface, supporting the idea that the spot is made of ice.

But for some reason Spot 5the brightest feature seen on Dawndoes not show up in infrared images. One possibility is that we still dont have enough resolution to see it in the proper way, said Tosi.

Dawn has also shown that some parts of Ceres are pockmarked by impact craters, while other regions seem smooth. So far there seem to be fewer large craters on Ceres than expected, says the mission's principal investigator, Christopher Russell of the University of California, Los Angeles.

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Mystery of Ceres's Bright Spots Grows