THE WOODLANDS, TEXAS—A mysterious bright spot on Ceres, the largest object in the asteroid belt, is looking more and more like ice—and could even be emitting water vapor into space on a daily basis, Dawn mission scientists reported here today at the Lunar and Planetary Science Conference. The bright spot, simply called feature #5, had been noticed before by the Hubble Space Telescope as sitting within an 80-kilometer-wide crater. But the Dawn spacecraft, which went into orbit around Ceres on 6 March, is now close to resolving the feature, which is less than 4 kilometers wide (pictured).

Andreas Nathues, principal investigator for Dawn’s framing camera, says the feature has spectral characteristics that are consistent with ice. Intriguingly, the brightness can be seen even when the spacecraft is looking on edge at the crater rim, suggesting that the feature may be outgassing water vapor above the rim and into space. “Ceres seems to be indeed active,” he says.

The feature brightens through the course of the day, and then shuts down at night. Nathues says the behavior is similar to that of comets. Dawn should be able to resolve the feature completely, along with a smaller companion spot, when the spacecraft dips closer to the dwarf planet in mid-April.

Source: by Eric Hand