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How was the moon born?

During lunar eclipses, when the Earth interposes itself exactly between it and the Sun, the Moon turns reddish due to the scattering of red light by the Earth's atmosphere (Ph. Jonathan Leung via Flickr CC BY 2.0)

It was a huge cataclysm that gave birth to it! At least, scientists are sure. Even if they struggle to understand in detail how our satellite was born.

At the origin of everything, there was therefore a spectacular clash between the primitive Earth and a planetary embryo the size of Mars. Debris from the impactor and a fraction of the Earth’s mantle were thrown into orbit before coming together to form the Moon. This scenario, known as the giant impact, was established in 2004 thanks to numerical simulations carried out by Robin Canup, of the University of Boulder (United States).

Contrary to the hypothesis of gravitational capture or that of a fission of a piece of young Earth, it is the only one capable of accounting for the current dynamics of the Earth-Moon system.

But this scenario implies that the Moon should be composed of a mixture of 80% of the impactor and 20% of the Earth’s mantle, while we observe a strict geochemical similarity between the two stars!

THREE HYPOTHESES

Three hypotheses are now proposed to resolve this inconsistency. For Matija Cuk, of the Seti Institute (United States), and Sarah Stewart, of Harvard, it is enough to modify the speed of rotation of the Earth on itself at the moment of the impact with a planet of half of the mass of Mars to generate a Moon composed of 92% of terrestrial materials.

For Robin Canup, we must imagine an impactor of the mass of the Earth, producing a phenomenal cataclysm capable of mixing the materials of the young Earth and the impactor in a homogeneous way.

THE MYSTERY REMAINS

As for Willy Benz, from the University of Bern (Switzerland), he suggests a conventional impactor (the size of Mars), but much faster than previously imagined, and colliding with a rapidly rotating Earth on its axis.  With this abundance of scenarios, specialists still do not know how the moon was formed.

Let us add that they also ignore when it started to shine in our night sky. At least, their response varies according to the dating methods used and the simulations carried out. Decidedly, the star of the night is not about to reveal all its mysteries …

Source : Science & Vie 

Par Jules Bercy

A writer a blogger passionate about science, history politics, the general knowledge of our planet and the Universe...

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