Comet Data Clears Up Debate on Earth’s Water

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Source:  By Kenneth Chang, The New York Times

Excerpt: One of the first scientific findings to emerge from close-up study of a comet has all but settled a question that planetary scientists have debated for decades. The new finding, from the European Space Agency’s mission to the little duck-shaped comet called 67P/Churyumov-Gerasimenko, appears to eliminate the possibility that the water in Earth’s oceans came from melted comets. Water vapor streaming off the comet contains a higher fraction of “heavy hydrogen” than the water on Earth does, scientists reported on Wednesday. “That now probably rules out” comets as the primary source of terrestrial water, said Kathrin Altwegg, a scientist at the University of Bern in Switzerland and the principal investigator for the Rosetta instrument that made the measurements. With comets unlikely, most astronomers now think Earth’s water came from asteroids. ...The new findings, published in the journal Science, came after Rosetta arrived at Comet 67P in August, close enough for the instrument to begin detailed analysis of the molecules coming off the comet.  ...Earth may have been wet from almost the beginning.... See also: 2014 Dec 11 Science article.

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