Rosetta: Water the Earth does not come from comets – Le Point

The Earth’s water comes from asteroids that hit our planet there are 3.9 billion years, and not of cometary nuclei, suggest measures made by the Rosetta probe in orbit around Churyumov-Gerasimenko of the comet where the Philae robot landed in November. “We must conclude that the Earth’s water was most likely made by asteroids than comets,” said at a press conference Kathrin Altwegg, Swiss Berne University, lead author of the study published Wednesday in the journal Science who, remember, sniffed the hair of the comet tchouri whose smell had proved pestilential. Using a spectrometer, the researchers determined that the atomic signatures of water molecules trapped near Churyumov was very different from that foun d on Earth.

In practice, scientists measure the ratio of deuterium, an isotope of hydrogen, and hydrogen, which forms the water with oxygen. “This ratio of deuterium to hydrogen (in the water molecules of the comet Churyumov, Ed) is probably the highest of all solar system bodies” and is three times that of water on Earth, said Professor Altwegg. So the ratio is 30 to 120% higher than that found in the water molecules of Comet Halley, which belongs to the same family comet, called Jupiter, formed in the Kuiper Belt. A deuterium / hydrogen ratio higher “means that the comet Churyumov formed at very low temperatures, probably in the early solar system,” there are 4.6 billion years, has determined the scientist.

“This result does not upset things”

However, the water found on asteroids has a ratio of deuterium / hydrogen much lower and seems more similar to the Earth’s water. Comets are rich in water, which is not the case of asteroids, some are even free. But, says Francis Rocard, head of the Rosetta program CNES, there were to date a lot more asteroid (650000) and comets (4000). “In my opinion, this result Rosetta does not upset things, but makes them a little more complex than previously thought, while strengthening the hypothesis asteroid” as the source of Earth’s water, says Francis Rocard. Indeed, “the ratio of deuterium / hydrogen from water varies from a comet to another, much more, apparently, than for asteroids and, for the moment, it is hard to navigate” says the scientist.

Professor Altwegg explained that the various measures of this ratio in the same family of comets could indicate different origins of celestial bodies. The researchers explain that the water in gaseous form from volcanic magma shortly after the formation of the Earth was blown by giant impacts with other objects, including the one that created the Moon. This primitive water would have disappeared. Then the world would have found water thanks to intensive bombing there is 3.9 billion years especially asteroid, according to this latest study. Items that the Japanese probe Hayabusa-2, part precisely to the assault of an asteroid, will perhaps enlighten.

But apart from the origin of the Earth’s water, the major objective of the Rosetta mission is also to determine the core composition of the comet Churyumov. But this task might be a little more complicated than expected since the drilling carried out by Philae, just before falling asleep, would, it seems, not work.