December 11, 2014

• Rosetta casts doubt on comets as Earth’s water providers

  

  Comet 67P’s atmosphere contains a surprisingly high fraction of deuterium By Ashley Yeager 2:00pm, December 10, 2014

  GETTING FUZZY  The basic chemistry of a comet’s thin, hazy atmosphere offers hints about how water got to Earth. It may not have been on the backs of comets like 67P/Churyumov–Gerasimenko.

   

  Data from the Rosetta mission are raising doubts about the idea that Earth’s oceans are filled with water from comets.

  The water in comet 67P/Churyumov–Gerasimenko’s thin, hazy atmosphere doesn’t chemically match Earth’s oceans, suggesting that asteroids, not comets, brought water to Earth billions of years ago, said planetary scientist Kathrin Altwegg of the University of Bern in Switzerland in a news conference December 9.

  Altwegg and colleagues used an instrument aboard the Rosetta spacecraft to measure deuterium, a heavy form of hydrogen, in comet 67P’s meager atmosphere, known as its coma. The results revealed that the comet’s water has a deuterium-to-hydrogen ratio roughly three times as high as water on Earth does, the team reports December 11 in Science.

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