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CO2 seen driving comet's 'jets'

College Park, Md. -- NASA's close encounter with comet Hartley 2 found dry ice is the fuel for jets of gas and dust bursting from the comet's surface, U.S. researchers say.

Images from the University of Maryland-led EPOXI mission flyby show spectacular jets of gas and particles shooting from many distinct spots on the surface of the comet, a university release said Wednesday.

Spectral analysis of the materials coming from the jets shows primarily CO2 gas (carbon dioxide) and particles of dust and ice, researchers said.

"Previously it was thought that water vapor from water ice was the propulsive force behind jets of material coming off of the body, or nucleus, of the comet," UM astronomy professor Jessica Sunshine said.

"We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet," she said.

"This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.
Scientists are studying images coming back from the spacecraft at the rate of 2,000 a day.

The latest discovery is an insight into the comet's chemistry and its formation, researchers say.

"The dry ice that is producing the CO2 jets on this comet has probably been frozen inside it since the formation of the solar system," UM planetary scientist Lori Feaga says.

Copyright 2010 United Press International, Inc. (UPI).

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