How was the moon formed? Israeli researchers shed new light on subject

Technion and French researchers: The moon was formed from Theia, not from Earth

April 13, 2015 02:26
2 minute read.
Theia Earth collision

Artistic image of collision between Theia and Earth. (photo credit: TECHNION)


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Scientists are sure that the moon is not made of cheese, but over the millennia, mankind has wondered about the composition, form and creation of the large object revolving around Earth. Now researchers at the Technion-Israel Institute of Technology in Haifa and the University of Nice have conducted a study that sheds light on these questions.

An integral part of determining the Jewish and Muslim calendars and considered a god in some traditions, the moon remains mysterious nearly five decades after American astronauts first walked on it.

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Research on the process in which the moon was formed was carried out by Technion Associate Prof. Hagai Perets and post-doctoral student Alessandra Mastrobuono-Battisti who worked with him in cooperation with Sean Rayman of the French university.

“Since the 1980s, a paradigm of the “Great Collision was bolstered,” said Perets. “According to this model, the moon was created from the debris of a collision between Earth and a celestial body called Theia that was half the Earth’s size and with a much smaller mass. Some of the material that was released as a result of the collision fell to Earth, some splashed out into space and the rest began to move as separate pieces into orbit. Gradually, they solidified into one object – the moon.”

Astrophysicists who study the moon’s formation have argued for at least four decades about the origin of the material from which it was created – debris from Earth or uprooted material from Earth or from Theia. It is now known from the study of such collisions that moons are created by material from the celestial body that causes the collision (Theia) and not the body that is hit (the Earth in this case).

But the great similarity between Earth and the moon – which was boosted by an analysis of material brought back from the moon by astronauts – raised the “suspicion” that the moon was nevertheless created from debris from Earth, said the Technion team, whose members have finally resolved the issue. They performed scores of simulations of planets created in the solar system and found much similarity between the planet and the bodies that hit them. Thus they concluded that the similarity between Earth and its moon results from the similarity between Theia – from which the moon was created – and Earth.

This means that “the history of Theia brought it, and not other bodies, close to Earth,” explained Mastrobuono-Battisti.

“In other words, Theia and the Earth grew in the same area, releasing debris from Theia, some of which became the moon.

“So we have settled the matter that has caused the scientific community to believe mistakenly that the moon formed from the Earth and not Theia.”

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