Sidereal Messenger: Moon was born suddenly from a giant impact, indicates simulation

The hypothesis that the Moon formed from a giant impact from the early Earth with a planetary-sized body the approximate size of Mars gained weight from new simulations carried out by the group of Jacob Kegerreis, from the University of Durham. , in the United Kingdom. And the result suggests that the Moon may have formed almost immediately after the collision, 4.5 billion years ago.

The general notion of how the Moon was formed is not new; the idea of ​​a giant impact between Earth and this hypothetical object, which astronomers call Theia, was born in 1975. It seemed the best way to elucidate how our planet ended up having such a proportionately large natural satellite. It was assumed that the giant impact ejected enormous amounts of matter into Earth’s orbit, which returned in a few million years to coalesce by gravity to form the Moon.

With the advancement of computing to allow detailed simulations of the process, especially since 2001, it was possible to visualize how this would have happened, but there were still pieces that did not fit together, such as the composition of the Moon. While the simulations suggested that much of the lunar mass would be derived from Theia, the composition of rocks brought back from the Moon by space missions indicated a much greater kinship with Earth itself.

Now, Kegerreis and colleagues have discovered that the problem between expectation and outcome was basically one of resolution. With the evolution of computers and access to machines with high processing power, it was possible to create a more detailed simulation than anything that had been done before – a hundred to a thousand times more than most previous efforts.

By simulating the impact between Earth and Theia by “breaking down” them into 100 million individual particles (which roughly corresponds to each particle having an actual size of 14 km, comparable to the asteroid that killed the dinosaurs), they found that everything fit in much more naturally. And the Moon, instead of forming from a disk of debris after the impact, was born practically ready in the impact itself.

The work, published in the Astrophysical Journal Letters, also shows how the Moon could have acquired a more predominant composition of Theia in its interior and more similar to Earth itself in the outermost layers – corroborating what is observed, at least superficially, based on lunar samples.

The one-step model of Moon formation also harmonizes well with orbital parameters such as tilt and period (increasing since then). But the most incredible thing is watching the videos of the simulations, in which an apparently delicate and malleable dance (actually a colossal and violent cataclysm), based on gravity, pressure and hydrodynamics, produces the beautiful pair that billions of years later we would call our home. and its great cosmic companion.

This column is published on Mondays, in Folha Corrida.

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