The water “tchouri” is different from that of the Earth – The World

Le Monde | 12/10/2014 at 20:01 • Updated 12/11/2014 at 11:14 | By David Larousserie

No, the Earth has not watered the sole source icy comets. In other words, the water of the Earth’s oceans may be of a different nature from that in the core of some of these vagabonds stars that in their rounds around the Sun, deploying a long queue of several million kilometers.

This is one of the first conclusions of the Rosetta mission of the European Space Agency since August, flies and follows the comet 67P / Churyumov-Gerasimenko over 500 million kilometers from Earth. In the journal Science of 10 December, the international team of Rosina instrument installed on the probe made its long-awaited verdict on the water composition emitted by the comet.

For in the H ₂ O water, hydrogen, symbolized by H, are not all exactly the same. These atoms have indeed cousins, called isotopes, twice heavier deuterium, symbolized by the letter D. These may replace a light hydrogen to form water-related molecules, such as HDO. In our seas, three heavy atoms we sin 10 000 water molecules. But on “tchouri” is three times more, the researchers said.

“This measure deuterium ratio relative to hydrogen [D / H] in water is one of the most fundamental results of the mission, which was one of the major goals “, says Olivier Mousis, co-author and professor at the University Franche-Comté. “This result probably exclude the hypothesis that comets brought water to Earth. This could happen as a result of an asteroid bombardment by comets rather than “, said Kathrin Altwegg, Head of the instrument at the University of Bern, at a conference organized by the journal Science .

It is true that so far the measures on asteroids, or at least meteorites recovered on Earth, show no difference in . the composition of their water content with the ocean

Review the models

Asteroids are bodies orbiting closer to Earth as comets; the former being beyond the orbit of Mars, the second as “tchouri” parked generally well beyond that of Neptune. They are also less “active”, the nucleus, which contains less ice, no degassing its water as do comets. It was during the period known as the great bombardment, that 800 million years after the beginning of the formation of the solar system, asteroids have fallen in large numbers on Earth.

So exit comets as the main source of water for the Earth. But not as a source of mystery. This result is indeed not consistent with the measures issued in 2011 on another comet of the same family as “tchouri” Hartley-2. The latter has as little deuterium than terrestrial oceans – three times less than found today Rosetta

While the techniques used are not identical. Hartley-2 was investigated using the Herschel space telescope that locates the “color” of the gases to millions of miles away. While the composition of the water “tchouri” was determined by an “electronic balance” molecules are counted according to their mass, less than one hundred kilometers from the target. “We can only say that for now, the water composition of the same comet could be measured by two different instruments” , says Dominique Bockelée-Morvan, who has worked with Herschel and is involved in Rosetta at the Laboratory for Space Studies and Instrumentation in Astrophysics in Paris.

But the most plausible explanation is that astronomers should revise their models. Although the two comets have rather similar orbits and short trips around the sun, they would not have formed in the same place around the sun. The first probably closer to the star than the second.

“fantastic result”

The theories stipulate that the chemical processes exchanging the deuterium hydrogen depends on the distance from the Sun, enrichment being stronger away from the star. Then a complicated gravitational history would have somehow reconciled. These events or otherwise explain also, conversely, much more “distant” of orbits comets like Halley have deuterium reports intermediaries between hydrogen Hartley-2 and 67P / Churyumov-Gerasimenko!

“We begin the science phase of the mission by a fantastic result. And there will be many others, “, warned Matt Taylor, the chief scientist of Rosetta to the European Space Agency. There will not be long to wait for next week, new results will be presented at the American Geophysical Union conference. Articles in the journal Science are also announced for late January.