ESA Rosetta Spacecraft Reveals Daily Water-Ice Cycle on Comet

First Posted: Sep 25, 2015 09:56 AM EDT

ESA's Rosetta spacecraft may reveal a bit more about how comets "stay alive" with their daily water-ice cycle. By learning a bit more about this cycle, researchers are learning a bit more about comets in general.

Comets are celestial bodies comprising a mixture of dust and ices, which they periodically shed as they swing towards their closest point to the sun along their highly eccentric orbits. As sunlight heats the frozen nucleus of the comet, the ice in it turns directly into gas. This gas then flows away from the comet, carrying dust particles along with it. Together, gas and dust build up the bright halo and tails that are characteristic of comets.

In this case, Rosetta sent back data from Comet 67P/Churyumov-Gerasimenko, which the spacecraft has been studying for close to over a year.

Currently, researchers are looking at how activity on the comet and the associated outgassing are driven. The researchers have actually recently identified a region on the comet's surface where water ice appears and disappears in sync with its rotation period.

"We found a mechanism that replenishes the surface of the comet with fresh ice at every rotation: this keeps the comet 'alive,'" said Maria Cristina De Sanctis, lead author of the new study, in a news release. "We saw the tell-tale signature of water ice in the spectra of the study region but only when certain portions were cast in shadow. Conversely, when the sun was shining on these regions, the ice was gone. This indicates a cyclical behavior of water ice during each comet rotation."

The findings suggest that water ice on and a few centimeters below the surface "sublimates" when illuminated by sunlight, turning it into gas that then flows away from the comet. Then, as the comet rotates and the same region falls into darkness, the surface rapidly cools again.

The new findings reveal a bit more about this comet and the processes that it undergoes. This, in turn, could help scientists better understand other comets.

The findings are published in the journal Nature.

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TagsRosetta, ESA, Comet, Comet 67P/Churyumov-Gerasimenko, Philae, Rosetta Mission, Spacecraft, space