These lunar meteorites contain gases originating from… Earth

Information that could well put an end to the debate on the origin of our satellite.

When they analyzed six lunar meteorites found in Antarctica by NASA, Swiss researchers affiliated with the prestigious ETH Zurich made an astonishing discovery; they determined that these pieces of rock originating from our satellite harbored chemical elements that came directly… from inside the Earth. A conclusion that might seem delusional at first sight; but it actually represents the pfirst almost indisputable proof of an old hypothesis on the history of our planet.

To understand the ins and outs of this work, we must go back to the origins of the Moon. About 4.5 billion years ago, a few hundred millennia after the formation of the solar system, the context was very different.

At the time, Earth was still just a juvenile planet, a big clump of clumped material that hadn’t even been completely cooled. And above all, she evolved alone; the Moon was not yet part of the landscape at that time.

To try to determine its origin, astronomers have reviewed a lot of scenarios. But none has succeeded in providing indisputable proof that would make it possible to decide in favor of this or that track. But there is one in particular that still wins the support of the majority of researchers: thegiant impact hypothesis.

Terrestrial chemical signatures in the middle of the Moon

It suggests that the Moon was born from a cataclysmic collision between this early Earth and another massive celestial body. Its size would be comparable to that of Mars, a little more than half of our planet. This object, named Theiawould have crashed into our future cradle head-on at more than 40,000 km/h.

The impact would have been so violent that part of the Earth’s mantle would have immediately liquefied, giving way to a vast ocean of molten rock. A large amount of material would also have been vaporized and catapulted into orbit, joining the remains of Theia, too. sprayed on site. All this material would then have agglomerated once again to form a new celestial body: the Moon.

This hypothesis is today favored by specialists, because it is consistent with observable reality. The problem is that there is still a lack of concrete elements that would make it possible to remove the last doubts once and for all; and this is perhaps what the Swiss planetologists have just brought.

A section of a lunar basalt sample whose crystal structure has trapped noble gases originating from Earth. © ETH Zurich / Patrizia Will via EurekaAlert

They are in any case formal on one point; there is no doubt that some of the chemical elements found in these meteorites did indeed come from the Earth. In any case, they put forward several extremely solid arguments; all are based on chemical signatures spotted using a device like no other.

The machine, dubbed Tom Dooley (some will recognize a reference to the Grateful Dead), is indeed the most accurate noble gas spectrometer in the world. It has allowed researchers to focus on the presence of very specific “variants” (or more precisely, isotopes) of certain noble gases, such as helium and neon. Usually, researchers associate their presence with the influence of the solar winds that sweep across the surface of the planets.

The origin of the Moon is now almost certain

But here, the meteorites came from material that crystallized in the depths of the Moon, not on the surface. They should therefore have been protected from the influence of the solar winds. Yet it still exhibited those famous isotopic signatures; this suggests that it was still exposed to this stream of particles at the time of its crystallization.

According to the researchers, the impact between Theia and the Earth would therefore be the only scenario that could explain the transfer of this “isotopic signature” in the middle of the moon. These rocks would have formed from material originating on Earth that already exhibited these signatures. ” Finding solar gases for the first time in basalt material on the Moon, unrelated to surface exposure, was a very exciting result. “, concedes Patrizia Will, doctoral student at ETH associated with the study.

These are undoubtedly some of the most convincing elements in favor of this theory. It’s not not yet an absolute and definitive confirmation, but it’s just like ; the case is now stronger than ever. Exceptionally convincing elements would have to be provided to persuade specialists to favor a different hypothesis.

A rush for noble gases?

And the other good news is that the scope of this work could even be greater than expected. Indeed, the study of noble gases has often been relegated to the background by researchers. This is partly because they are perfectly inert; they do not participate in chemical reactions from which researchers can deduce a great deal of information.

But according to Henner Busemann, a professor at ETH and a world-renowned authority on extraterrestrial geochemistry, the exploits of the Tom Dooley spectrometer may well encourage other planetary scientists to take a closer look at noble gases.

I am strongly convinced that there is going to be a race to study noble gases and their isotopes in meteoritic materials”, he predicted. “This knowledge could help chemists and physicists create new models to show how such volatile elements can survive planet formation, in our solar system and beyond.”

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