Not years or months: it took a few hours for the Moon to take shape from the carom of debris generated billions of years ago by the catastrophic impact of Theia, a planet the size of Mars, with the Earth. This is the scenario that emerges from the most detailed simulations conducted so far on the birth of our natural satellite, which promises to revolutionize knowledge on the evolution of the Moon and to answer many unanswered questions. Published in The Astrophysical Journal Letters, the new data is due to the collaboration between the British Durham University and the Ames Research Center of NASA, in the United States.
“We found that gigantic impacts can immediately give rise to a satellite with mass and iron content equivalent to that of the Moon,” the researchers, coordinated by Jacob Kegerreis of the Ames research center, write in the article. The simulations indicate that the debris generated by the impact of Theia with the Earth would have ended up on the same orbit, at a point beyond the minimum distance, called the Roche limit, which allowed such a rapid process of aggregation. , beyond which a smaller body that orbits around a larger one remains cohesive, without fragmenting.
Another important thing that the simulations are able to explain is the composition of the Moon, 60% similar to that of Earth, along with its inclination. The theories accredited so far on the origin of the Moon allowed to reconstruct only some aspects, such as its mass and orbit, but left other important questions open, starting from the great similarity between the composition of the Moon and that of the Earth. Some theories propose that the fragments of Theia thrown into space after the impact had mixed only with a small amount of terrestrial material, while others point to the coincidence that Theia could have a composition similar to that of our planet: they are examples that still leave many open questions.
The new theory of very rapid formation is at the moment the simplest, most complete and elegant; according to the researchers, it is also the starting point for solving other problems, such as those of its inclined orbit and its thin crust. The definitive confirmation of the accuracy of the new scenario can be given, however, only by the Moon: an important help could come, for example, from the analysis of the lunar rocks that the future missions of the Artemis program will bring to Earth. Being able to study rocks that come from different points on the lunar surface and subsoil will mean being able to compare their real characteristics with those predicted by the simulations.
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