By Ron Cowen
Small but spunky, hyperactive Comet Hartley 2 is shaped like a peanut and spews several jets of gas and dust on both its day and night sides, NASA’s EPOXI spacecraft has revealed. Intriguingly, the activity of the comet appears to be driven by the sudden venting into space of frozen carbon dioxide — dry ice — rather than frozen water, as has been found to be the case with many other comets, said principal mission scientist Mike A’Hearn of the University of Maryland in College Park.
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It’s the emission of carbon dioxide, rather than frozen water, that waxes and wanes most dramatically as the active portions of the comet rotate in and out of sunlight, he noted during a November 4 press briefing at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., just a few hours after the craft passed within 700 kilometers of the elongated object.