The moon would have formed in a few hours

This article is from the December 2022 issue of Science et Avenir – La Recherche N°910.

4.5 billion years ago, a Mars-sized protoplanet collided with the early Earth. Ejected into space, debris gradually accumulated to form our natural satellite. This is the scenario scientists have favored since the 1980s to explain the moon’s origin. But experts struggle with the exact circumstances of this phenomenon.

New digital simulations

“Models struggle to reproduce all the characteristics of the star, such as its precise orbit or the very large chemical similarities between the terrain and lunar rocks. “, emphasizes Frédéric Moynier, a cosmochemist at the Institute of Earth Physics in Paris. However, numerical simulations carried out by NASA and planetary scientists from the University of Durham (United Kingdom) indicate that our celestial companion would have formed, not in months. Or even years, as previously thought. But in a few hours!

400 collisions were tested on the supercomputer

The team used the Cosma supercomputer, whose power is equivalent to 40,000 personal computers. 100 million particles of the Earth-Moon system were taken into account, compared to 100,000 to 1 million in previous work. A further 400 collisions were simulated with unprecedented resolution, with various parameters such as impact mass, composition and trajectory.

By doing so, the researchers were able to identify methods that would best reproduce the characteristics of the Moon. A celestial body in an orbit far enough away from the layers of material ejected into space would have accumulated and stabilized within ten hours. They must be made of 60% material from the primitive Earth, with the rest coming from the protoplanet. A larger rate than we imagined, especially in the surface layers of the Moon where the material cooled and coalesced before forming a thin crust.

This new structure explains the great similarities between terrestrial and lunar rocks, as well as the orbit and structure of our satellites. “It is a bewitching theory, Judge Frederick Moinier. However, American and Chinese missions in the coming years should be supported by the collection of new lunar samples at the South Pole and especially farther away, as planned. “