The Moon cheats on its age: it is ultimately older than expected!
Highly volcanic period of the Moon during which it was also much closer to Earth. © Generated on Grok by Brice Haziza
All children know that the Earth was hit by a giant “meteorite” long before the dinosaurs, and that this cataclysmic impact gave birth to the Moon. In fact, in terms of a giant meteorite, the scientific community tends to agree on a wandering planet the size of Mars and named Theia. In summary, this is the scenario commonly used to explain the chemical composition of lunar rocks, so close to that of rocks in the Earth's mantle.
The rocks brought back by NASA's Apollo missions, 55 to 52 years ago, confirmed this hypothesis and made it possible to estimate the age of the Moon at that of a young girl of only 4.43 or 4.51 billion of years. A young girl compared to Earth and its 4.55 billion years, of course.
A little flirtatious, the Moon manages to cheat about her age
The age of our celestial companion has been calculated using several methods, e.g. dynamics of the solar system and the chemical analysis of its rocks. However, the different processes do not agree by several hundred million years. The three authors of a study published in Natureall great specialists in their field, say they have understood why: the Moon is very flirtatious and lies about her age by simply putting on makeup.
It should be remembered here that during its formation, the Moon was between 15 and 20 times closer to the Earth. The gravitational tidal forces of one on the other were then colossal, between 3000 and 8000 times stronger than today!
The researchers were interested in the period when the satellite orbited three times closer to our planet with tides 27 times more powerful. The volcanism induced by the latter was therefore very violent, reshaping the surface of the Moon. Geologists previously thought that an age of 4.35 billion years could correspond to its formation, but the authors of the latest study say that the zircon found in lunar samples does not indicate cooling after the original giant impact. This is a remelting of the ground due to the orbital movements of the Moon.
Powerful volcanism likely reset the Moon's geological clock
Calendar of events proposed by this study. © Nimmo et al, Nature 2024
“Powerful volcanism likely reset the Moon's geological clockexplains Thorsten Klein, co-author of the study. The lunar rock samples therefore do not reveal their original age, but only the period when they were strongly heated.” The Moon would therefore have an age much closer to that of the Earth, which does not displease specialists in the history of the Solar System, who tend to think that giant impacts must have been much rarer after the first millions of years from our space cradle, then very chaotic…
To finish, here is a simulation of the history of impact basins on the Moon, the Great Bombardment:
