Ice In Ceres' Craters Is Linked To Its Axial Tilt

Posted: Mar 27 2017, 12:53am CDT | by , Updated: Mar 27 2017, 1:05am CDT, in News | Latest Science News

 
Ice in Ceres' Craters is Linked to Axial Tilt
Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Permanently shadowed regions on the dwarf planet Ceres maintain water ice

Dwarf planet Ceres contains water ice within its craters. And researchers believe that this frozen water on Ceres craters is accumulated by its axial tilt.

Since ice could only survive at extremely cold temperatures, there is a possibility that icy craters on Ceres surface might have not received sunlight for millions of years. However, researchers from NASA's Dawn mission calculate that the axial tilt or the angle at Ceres rotates around the Sun has shifted drastically over the course of about 24,500 years and brought changes to the craters as well.

“We found a correlation between craters that stay in shadow at maximum obliquity, and bright deposits that are likely water ice," said Anton Ermakov, a researcher at NASA's Jet Propulsion Laboratory and lead author of the study. "Regions that never see sunlight over millions of years are more likely to have these deposits.”

By using Dawn spacecraft measurements of shape and gravity, researchers have precisely reconstructed the changes in Ceres orientation over time and found that the dwarf planet has gone through cycles where its tilt ranged from about 2 degrees to about 20 degrees during the past 3 million years. The last time the dwarf planet reached a maximum tilt of 19 degrees was about 14,000 years ago.

The axial tilt determines weather patterns on a planet or any other cosmic object. When the axial tilt is small, relatively large regions of an object's surface do not receive direct sunlight. For comparison, Earth is tilted 23.5 degrees and this significant tilt causes seasons like summer and winter on Earth. By contrast, Ceres' current tilt is very small, about 4 degrees. So, its massive area including polar regions never receives sunlight. But when the axial tilt increases, most of the craters at the poles receive direct exposure to the sun and leaves a very small area of permanent shadow where water ice can exist.

According to calculations, only four persistently shadowed regions remain in shadow at the maximum 20-degree tilt in both northern and southern hemisphere and most of these regions have bright deposits today. These craters with areas that stay in shadow over long periods of time are called “cold traps.” If ice on these regions is exposed to direct sunlight it evaporates into space.

"The idea that ice could survive on Ceres for long periods of time is important as we continue to reconstruct the dwarf planet's geological history, including whether it has been giving off water vapor.” Co-author Carol Raymond, deputy principal investigator of the Dawn mission said.

Ceres is one of the only three third bodies in solar system that has permanently shadowed regions. Mercury and Earth's moon are the other two. The ice on Ceres is either came from the dwarf planet itself or may be delivered by impacts from asteroids and comet. Nevertheless, new findings offer a compelling view of the Ceres’ dynamic past.

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