Rosetta Comet’s Water Is Not Like Earth’s

Scientists now believe that water on Earth most likely did not come from comets. After a thorough study of the the water content on Comet 67P, the Rosetta orbiter has determined that the type of water found on the rock is much heavier, containing three times more deuterium than the hydrogen-oxygen compound found here on Earth.

Why this is significant is because for a time scientists believed that comets may have carried water to Earth, and that is how we formed our liquid oceans. Now that theory is likely discredited, and scientists believe that it is more likely that our water may have come from asteroids.

From USA Today: 

Even though one other Kuiper Belt comet has shown a water signature similar to Earth’s, the authors think asteroids, which developed nearer to our sun, were more likely the celestial tankers that slammed into the planet long ago.

“The conclusion here is that in the reservoir of the Kuiper Belt, we have very diverse comets that probably came from different regions of the early solar system,” lead scientist KathrinAltwegg, of the University of Bern, Switzerland, told the BBC.
“We have light water in some comets and very heavy water in other comets. We have to assume the mixture of all these comets is something that is heavier than what we have on Earth, so this probably rules out Kuiper Belt comets as the source of terrestrial water.”

But not everyone agrees, so the mystery remains complicated.

“In the end, Earth’s oceans are probably a mix of many things,” Altwegg said in an interview with New Scientist.

The Rosetta Landing Documentary

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