Sublime Surprise: Rosetta's Comet Cycles its Ice

Source: Discovery News

Sublime Surprise: Rosetta's Comet Cycles its Ice

SEP 23, 2015 01:00 PM ET // BY IRENE KLOTZ

Scientists have discovered an unexpectedly regular cycle of ice formation and depletion on the surface of a comet, a pattern tied to an orbital dance of shadow and sunlight.

Measurements taken by the European Space Agency’s Rosetta spacecraft, currently orbiting comet 67P/Churyumov-Gerasimenko, show that ice builds up when a particular region of the comet is in shadow. The ice then transitions, or sublimates, to gaseous water vapor when that region shifts into sunlight.

“We observed this cycle for several comet rotations … We were surprised to see so clearly the appearance and disappearance of the ice due to temperature and illumination conditions,” planetary scientist Maria Cristina De Sanctis, with the Institute for Space Astrophysics and Planetology in Rome, wrote in an email to Discovery News.

The finding helps resolve a puzzle about why a comet’s surface can be relatively free of ice, such as what has been observed on 67P and other comets, even though the bodies are outgassing water. The cycle of condensation and sublimation shows how water ice can be transported from the interior of the comet to the surface.

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