Friday, December 12, 2014

Asteroids, Not Comets, Brought Water to Earth's Oceans?

A photo of comet 67-P
This image of comet 67P is made up of four photographs taken by the Rosetta spacecraft.

Photograph by ESA/Rosetta/NAVCAM

By Dan Vergano

Asteroids, not comets, likely delivered Earth's ancient oceans from space, concludes a Wednesday study from the Rosetta spacecraft, now in orbit around a comet that is a frozen relic from the dawn of the planets.

Where did the Earth's oceans come from? the new study asks, investigating a long-debated question of whether the water on our planet's surface was delivered during a bombardment of comets some 3.8 billion years ago. Not likely, mission scientists conclude, pointing instead to ancient asteroids, which were covered with frost in the early solar system.

"Terrestrial water was probably brought by asteroids," says Rosetta study leader Kathrin Altwegg of the University of Bern in Switzerland. She finds that source "more likely than comets."

These are the first scientific results from the European Space Agency craft, which is orbiting the lumpy 2.5-mile-wide (4.1 kilometers) comet 67P/Churyumov-Gerasimenko, the mission team reports in the journal Science.

Rosetta arrived at the lumpy ice ball last month, delivering a probe that lost power and went into hibernation during its first days on the comet. Comet 67P is now more than 260 million miles (418 million kilometers) from the sun, awaiting a solar warm-up that will spark its cometary tail.


Source: National Geographic Magazine.

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