Magazine article Science News

Oxygen in Comet Surprises Scientists: 67p's [O.Sub.2] Molecules Probably Came from Solar System's Birth

Magazine article Science News

Oxygen in Comet Surprises Scientists: 67p's [O.Sub.2] Molecules Probably Came from Solar System's Birth

Article excerpt

A comet is leaking oxygen molecules that appear to have been buried since the beginning of the solar system.

The Rosetta spacecraft detected [O.sub.2] around comet 67P/Churyumov-Gerasimenko, the first time these molecules have been seen around a comet. The oxygen is probably primordial, trapped in water ice as the comet was assembled roughly 4.6 billion years ago, researchers report in the Oct. 29 Nature. Andre Bieler, a planetary scientist at the University of Michigan in Ann Arbor, and colleagues detected the oxygen using a mass spectrometer on board Rosetta, which has been orbiting comet 67P since August 2014 (SN: 9/6/14, p. 8).

"This is the most surprising discovery we have made so far," study coauthor Kathrin Altwegg said at a news briefing on October 27. Researchers did not expect to find oxygen in the fog of gas surrounding a comet. Oxygen is highly reactive, and theories about the formation of the solar system indicate that [O.sub.2] should have quickly interacted with hydrogen to form water. "When we first saw it, we all went into a little bit of denial," said Altwegg, of the University of Bern in Switzerland.

Oxygen's presence supports the long-held assumption that comets are pristine fragments from the dawn of the solar system. Comet 67P must have been put together gently, Bieler says; otherwise the ice-coated grains that make up its bulk would have been heated and the oxygen removed. Because the grains have not been heated, they are unprocessed time capsules--frozen samples that preserve the conditions that prevailed when the planets were forming.

Ultraviolet light from the sun and free-range electrons probably created the [O.sub.2] in the first place. In this scenario, high-energy photons and particles zapped water molecules, which re-formed into molecules of oxygen (and hydrogen). The oxygen was then trapped within ice that collected on dust grains, which in turn came together to assemble the comet. There, the oxygen stayed protected for nearly the age of the solar system. As recently as 1840, comet 67P was far enough out in the solar system to escape the sun's destructive influence, but an encounter with Jupiter nudged it in closer. …

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