The explosion of the old magma ocean on Earth could have led to the formation of the moon

The Earth-Moon system is one of the unique features of the solar system. The Earth is the only rocky planet with such a large moon and the only planet, apart from Pluto, to have a moon so similar to its composition. The Pluto-Charon system is also very different from the Earth-Moon system, leaving our planet in a category of its own.

The problem is that we never had a completely satisfactory model of the creation of the Moon. The hypothesis of the giant impact has dominated for decades. The theory is that shortly after the formation of the Earth, a protoplanet about the size of Mars hit it. This material mixed between the impactor, named Theia (mother of the moon, Selene, in the Greek myth), and the Earth.

As we learn more about the Earth-Moon system, researchers have struggled to use this idea to explain all the characteristics of both. Some features, such as high kinetic moment and almost identical isotopic ratios between the Earth and the Moon, when most models suggest that the Moon should contain a significant amount of Theia material, have been difficult to solve, requiring conditions narrow prerequisites to explain the relationship. to see today. A new theory on how to do this indicates that the Moon is much more logical if it hits the Earth while it is still partially melted.

One of the difficulties in explaining the similarities between the Earth and the Moon is that the rock is inherently difficult to mix. It takes a lot of energy to liquefy it and it is difficult to ensure that the liquefied rock mixes evenly between two impactors. But as researchers currently suggest, if the Earth still had an ocean of magma at the moment of impact, some of these problems are solved. The still liquid rock is much easier to mix and it takes less energy overall to transform the system.

The new chronology of impact events theorized with an ocean of magma presumed to exist. Click to enlarge.

The execution of the model with an ocean of liquid magma on Earth produces new results compared to the old solid model. About half of the magma movement is eventually ejected into the space, with some of the original impactor. The iron left by the collision continues to sink in the heart of the Earth, as expected, but a larger fraction of Earth's materials is suspended in orbit to merge with what remains of Theia.

The net effect of this model is to expand the total number of collision possibilities that would still create a moon with the features we see today. Since we obviously can not go back in time to observe what really happened, an important question for the models we use to examine what could have happened is their low density. If there are many different ways to create a given system, this is generally considered to be a better proof than to rely on a single set of very specific circumstances that would lead to a given result, not because that's the case. is impossible – highly improbable things happen all the time – but because it's inherently more difficult to validate.

Japanese researchers hypothesized that many rocks still floated in the wake of the formation of the solar system. If the Earth had been hit by smaller but still massive impactors before Theia, it could very well have had an ocean of magma. This model is not the last word of the Earth-Moon system, but it opens up more possibilities as to how it was created.

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