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University of Michigan instrument providing important data from Comet 67P

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ANN ARBOR, Mich. – An instrument designed and built at the University of Michigan's Space Physics Research Lab and flying aboard the European Space Agency's Rosetta spacecraft has provided new data from Comet 67P that is rewriting theories about how Earth got it's water.

It is thought that comets brought most of our water, but that theory now has come into question.

U of M's Double Focusing Mass Spectrometer is studying the water that comprises Comet 67P's ice, and it turns out that the comet's water is different than the water we have here on Earth.

"It is arguably the highest resolution instrument of its type to have ever flown in space. It can distinguish between different molecules that have nearly the same mass," said Bruce Block, lead engineer in research at the U of M Space Physics Research Lab.

And that high resolution is paying big dividends.

Did you know that there are different "kinds" of water? The chemical symbol for water is H20, which is two hydrogen atoms and one oxygen atom. If one or both hydrogen atoms has an extra neutron, then the molecule becomes a heavier version of water, called deuterium. U of M's mass spectrometer has determined that Comet 67P has a ratio of heavy water to "regular" water that's twice the ratio of what we have on Earth.

"Because this ratio has only been determined in a handful of comets, the results may indicate that there is a wider distribution in comets and that Earth's oceans might not have derived most of their water from comets," said Michael Combi, of the Freeman Devold Miller Collegiate Research Professor in the Department of Atmospheric, Oceanic and Space Sciences.

So if our water didn't come from comets, where did it come from?

Scientists have determined that meteorites originally hailing from asteroids in the Asteroid Belt match the composition of Earth's water. Thus, despite the fact that asteroids have a much lower overall water content, impacts by a large number of them could still have resulted in Earth's oceans.

As is the case with many space research missions, the data received generates as many questions as it answers.

"None of the other planets in our solar system are covered with water, so it would be nice to understand why we have a place that is so conducive to life, that is -- with a lot of liquid water on the surface," Combi said. "We would like to know where the water came from."

Rosetta, and the U of M mass spectrometer, will accompany Comet 67P for the next year on its path closer to the sun, and analyze more of the comet's composition as heating from the sun causes ice to sublimate and release gases and other material -- which then will form the comet's familiar tail.

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