Rosetta Results: Comets "Did Not Bring Water To Earth"

An anonymous reader writes with findings from the Rosetta mission which suggests water on Earth probably came from asteroids, and not comets."Scientists have dealt a blow to the theory that most water on Earth came from comets. Results from Europe's Rosetta mission, which made history by landing on Comet 67P in November, shows the water on the icy mass is unlike that on our planet. The results are published in the journal Science. The authors conclude it is more likely that the water came from asteroids, but other scientists say more data is needed before comets can be ruled out."

Comments

Re: Oh it's asteroids now?

[Firethorn]

The theory is that the protoearth lost all its water when the impact that formed the moon happened. That impact reliquified the planet, driving off the lighter elements. Ergo we had to be reseeded somehow.

Actually...

[NotSanguine]

The more informative article from the ESA website says that the Deuterium/Hydrogen (D/H) isotope ratio is significantly higher (more than three times, in fact) than that of water found on Earth.

However, The comet in question is not of the same type and composition as *all* comets. In fact, comets (even those that generally share orbits with the one sampled) vary widely in their D/H ratios. As such, the paper does not claim that comets didn't bring water to Earth, merely that comets like the one sampled (comet 67P/Churyumov–Gerasimenko) by ROSINA did not bring water to Earth.

From the better TFA:

Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water, in observations made by ESA’s Herschel mission in 2011. [Emphasis added]