The "Winchcombe meteorite" lets write a story of water on Earth
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Analysis of the composition of the water present in the “Winchcombe meteorite”, published on Wednesday, shows that it has a composition very similar to that of the Earth’s oceans. Sufficient proof that the water on Earth was brought there by meteorites?

A small rock found in 2021 in a private driveway in the small town of Winchcombe in central England may hold the answer to the mystery of the origin of water on Earth.

It is, in fact, a meteorite fragment from the depths of space and time which has begun to reveal its secrets in a study published Wednesday, November 16 in the journal Science Advance.

No terrestrial contamination

“The chemistry of the water contained in the ‘Winchcombe meteorite‘ [c’est devenu son nom officiel, NDLR] is quite similar to what is found in our oceans on Earth. The results of the analyzes carried out thus provide grist for the mill for the supporters of the theory according to which it was meteorites derived from asteroids which brought water to Earth at the beginning of its history, “says Katherine Joy, l one of the co-authors of the study and a specialist in the study of meteorites at the University of Manchester.

It is neither the first nor the last meteorite to fall on Earth that contains water. About 60,000 have been discovered, and “there are almost always scientists who analyze the water found there”, underlines Jérôme Aléon, cosmochemist and specialist in meteorites at the Institute of Mineralogy, Physics of Materials and cosmochemistry of the CNRS at the University of Sorbonne University.

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But the results are often to be taken with tweezers because “meteorites generally lie around for weeks, even months in the ground before being discovered, which leaves them ample time to be contaminated by the terrestrial environment”, specifies Luke Daly, co-author of the study and planetary scientist at the University of Glasgow.

This is not the case with this sample. It was discovered and collected less than 12 hours after landing in the heart of the British outback. It is too short for a significant contamination of this fragment, and “in addition, it had not even rained, which is not very frequent in England at that time”, remarks Katherine Joy.

All the matter contained in this sample – including water – therefore comes directly from space. More precisely, this meteorite would have detached from the asteroid belt around Jupiter and crossed 4.56 billion years to reach us. “It represents a snapshot of the origin of our solar system, and how celestial dust aggregated to form the first planets in the universe”, summarizes Katherine Joy.

“To our knowledge, this is the first witness of this time and this place in the galaxy containing water that resembles what is on Earth that we have been able to analyze”, enthuses Luke Daly. They have the same chemical signature, which means they could come from the same place because part of the composition of water depends on the distance from the sun.

Multiple stories of water

This first study of the “Winchcombe meteorite” thus suggests that our oceans are filled with water that would come from Jupiter’s asteroid belt or further (the asteroids there probably drifted from regions outside of Jupiter). our solar system).

But these first analyzes are not enough to close the debate on the origin of water on Earth, “far from it”, assures Luke Daly. “This is an element that reinforces those who defend the theory of water brought to Earth by asteroids, but it does not close the door to other hypotheses”, adds Jérôme Aléon.

First of all, even if asteroids played a role, they may not be the only ones to have covered almost 70% of the earth’s surface with water. “One theory would, for example, say that grains of space dust participated in the formation of the oceans”, notes Luke Daly. These are tiny particles floating in space which, in contact with the solar wind, are charged with water. At the beginning of our history, they would have swept our young Earth to deposit their precious H2O.

“Another theory is that it was comets that brought water to Earth,” says Katherine Joy. But for now, studying the ice on comets can only be done remotely with tools like telescopes. This is insufficient to get a clear idea of ​​​​the validity of this alternative theory and “what scientists would like is that a mission could allow us to bring back a piece of comet ice so that we can study in the laboratory to compare the composition of its water to that of our oceans”, continues the specialist from the University of Manchester.

Finally, there was perhaps also water already present on Earth from its beginnings. “Observations show that under the surface of different planets, including ours, there is water with the same chemical composition as that which is in our oceans and which could have already been there during their formation”, explains Jérôme Aleon.

The mystery of the creation of life

If the debate on the origin of water on Earth agitates scientists so much, it is “because it is a constituent element of the appearance of life on our planet”, notes Luke Daly. Analysis of the Winchcombe meteorite thus suggests that life on Earth was possible thanks to water that would come from further away than Jupiter.

This thesis of meteorites providing official water to the galaxy also leads one to wonder why life seems, until proven otherwise, to have developed only on Earth. Similar meteorites have surely not failed to fall on other planets.

Indeed, “the Winchcombe meteorite contains all the elements necessary for the creation of life on a planet”, recognizes Luke Daly. The whole question is then to know what the Earth has done that is unique in order to transform the test to make the first living organisms appear in this water.

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