Mystery solved? Spots on Ceres most likely ice

Chuck Bednar for redOrbit.com – @BednarChuck

A pair of mysterious bright spots detected on Ceres during the Dawn spacecraft’s approach to the dwarf planet appear to be made of ice, mission scientists reported Tuesday during the 46th Lunar and Planetary Science Conference in Houston, Texas.

[STORY: Uh, what are those bright spots on Ceres?]

The spots, which were originally detected by the NASA probe in February, were located in the same basin on the dwarf planet’s surface and reflected about 40 percent of the light that was hitting them. At first, it appeared that there was only one bright spot, but as Dawn drew closer to Ceres en route to its March 6 rendezvous with the dwarf planet, a second became visible, leaving us all baffled. What were these bright spots?

Experts were puzzled as to the potential origin of the bright spots. The presence of the second one hinted that they may have had a “volcano-like origin,” Dawn principal investigator Chris Russell has said previously. Ice was another possible explanation, as scientists had previously detected water vapor coming from the dwarf planet’s surface.

Ice, ice baby

While ice would probably reflect more than 40 percent of the light that hit it, the resolution limits of Dawn’s imaging equipment at its current distance may make it appear otherwise, the researchers explained. A third possibility was that the areas were patches of salt, but scientists could not say for sure until Dawn reached Ceres and collected more data.

Now, as Eric Hand of Science reported on Tuesday, it appears that those who chose ice in their “what caused those bright spots to form on Ceres” office bet are a little richer this morning. Not only that, but the ice may even be emitting water vapor into space on a daily basis, he noted.

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Officially known as “feature #5,” the bright spots were originally detected by the Hubble Space Telescope as resting within a nearly 50 mile (80 km) wide crater. Dawn has allowed scientists to get a better look at the feature, however, and is close to resolving the 2.5-mile (4 km) spots.

During the conference, Andreas Nathues, principal investigator for Dawn’s framing camera, explained that the spectral characteristics of the feature are consistent with ice, and that the fact that the brightness is visible even when the spacecraft is looking on edge at the crater rim seems to indicate that it is outgassing water vapor above the rim and into space.

“Ceres seems to be indeed active,” Nathues told Hand. The feature becomes brighter during the course of a day, and then appears to switch off at night – behavior that the Dawn scientist points out is similar to that of a comet.

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Ceres, the largest object in the asteroid belt between Mars and Jupiter, was the second location visited by Dawn. In 2011 and 2012, the spacecraft visited the giant asteroid Vesta, and while it was there, it collected over 30,000 images and several measurements of the object. As a result, scientists learned far more about its composition and geology.

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