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NASA's Dawn space probe maps permanent shadows on Ceres

Researchers with NASA's Dawn mission have identified regions on the dwarf planet Ceres that are likely to have been cold enough to trap water ice for a billion years.

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    Permanently shadowed regions capable of accumulating surface ice were identified in the northern hemisphere of Ceres using images taken by NASA’s Dawn mission combined with sophisticated computer modeling of illumination.
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Scientists with NASA's Dawn mission say they have uncovered Ceres' "darkest secret" with their identification of the dwarf planet's permanently shadowed regions.

In a study published in the journal Geophysical Research Letters, researchers describe the regions that do not receive direct sunlight, and their implications. Many of these regions have likely been cold enough to have trapped water ice for a billion years, scientists say.

"The conditions on Ceres are right for accumulating deposits of water ice," said Norbert Schörghofer, a Dawn guest investigator at the University of Hawaii at Manoa, in a statement. "Ceres has just enough mass to hold on to water molecules, and the permanently shadowed regions we identified are extremely cold – colder than most that exist on the moon or Mercury."

While these areas still receive indirect sunlight, many are cold traps due to temperatures below about minus 240 degrees Fahrenheit, researchers say.

"On Ceres, these regions act as cold traps down to relatively low latitudes," explained Erwan Mazarico, a Dawn guest investigator at Goddard. "On the moon and Mercury, only the permanently shadowed regions very close to the poles get cold enough for ice to be stable on the surface."

The team found dozens of permanently shadowed regions across the dwarf planet's northern hemisphere, with the largest inside a 10-mile-wide crater located less than 40 miles from the north pole. Altogether, the regions occupy about 695 square miles, less than 1 percent of the surface area of the northern hemisphere. Typically, they can be found on the crater floor or along a section of the crater wall facing toward the north pole.

To make the identifications, the researchers used images of Ceres' northern hemisphere taken by Dawn's camera (as seen in this video) to create a 3D map of the dwarf planet, complete with craters and plains. They then input the map into a computer model, which they used to determine the parts of the planet the sunlight reaches and how much radiation makes it to the surface.

The regions' existence on Ceres had been predicted, but the findings of Dr. Schörghofer and his colleagues marked the first time they had been identified.

In comparing the new findings to previous findings, the researchers found that the permanently shadowed regions on Ceres more closely resemble those on Mercury than those on the moon, as permanently shadowed regions on Mercury account for roughly the same fraction of the northern hemisphere. The ability of these areas on Mercury to accumulate water ice is also comparable.

"While cold traps may provide surface deposits of water ice as have been seen at the moon and Mercury, Ceres may have been formed with a relatively greater reservoir of water," said Chris Russell, principal investigator of the Dawn mission, based at the University of California, Los Angeles. "Some observations indicate Ceres may be a volatile-rich world that is not dependent on current-day external sources."

Researchers say the findings could not only help scientists better understand Ceres, but also have implications beyond the dwarf planet.

"Ceres is an ice-rich body to begin with," Schörghofer told Digital Trends. "The extra ice is significant because it may have the same origin as the ice on Earth's Moon."

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