Rosetta Spacecraft Hints that Earth's Water Didn't Arrive by Comet

It turns out that water on a comet is different from water on Earth. ESA's Rosetta spacecraft has discovered that the water vapor from its target comet is significantly different to that found on Earth, which could spark debate about the origin of our planet's oceans.

One of the major hypotheses of Earth's formation is that it was so hot when it formed 4.6 billion years ago, that any water should have boiled off. Obviously, there is water today, which means that it had to come from somewhere. Some scientists believe that this water was delivered when comets and asteroids collided with the surface of our planet.

And yet this latest findings throws some controversy on this theory. In the month following the spacecraft's arrival at Comet 67P/Churyumov-Gerasimenko, Rosetta took measurements. More specifically, it examined the proportion of deuterium, which is a form of hydrogen with an additional neutron-to normal hydrogen. This proportion reveals exactly where the water came from since in theory, it should change with distance from the sun.

It's believed that this comet were thought to have formed further out, in the Kuiper Belt beyond Neptune. Occasionally, these bodies are disrupted from this location and sent toward the inner solar system. Rosetta's comet, for example, now travels around the sun between the orbits of Earth and Mars.

Interestingly, the ratio measured on the comet is more than three times greater than for Earth's oceans and for its Jupiter-family companion, Comet Hartley 1. In fact, it's even higher than measured for any Oort cloud comet, as well.

"This surprising finding could indicate a diverse origin for the Jupiter-family comets-perhaps they formed over a wider range of distances in the young Solar System than we previously thought," said Kathrin Altwegg, one of the researchers, in a news release.

The findings reveal that water on Earth may not have originated from comets and asteroids. That said, scientists plan to continue their research with Rosetta as it follows the comet on its orbit around the sun throughout the next year.

The findings are published in the journal Science.

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