Moon Was Formed of Many Small Moons, New Theory Suggests

Have you ever wondered how the Moon was formed? And how well does the mankind actually know this most obvious and familiar object in our sky? The Earth’s only natural satellite and the question of how it was formed have always been a source of fascination.

Now, the team of Israeli scientists suggests the idea that the Moon as we know today, wasn’t actually its first form. The Moon is the amalgamation of many small moons or “moonlets”, formed by many smaller collisions.

Moon is the result of various collisions

This newly proposed theory by researchers Prof. Hagai Perets, of Technion, and Weizmann Institute Profs, Raluca Rufo and Oded Aharonson, contradicts the commonly held, but much unsatisfactory, “giant impact” paradigm.

According to this theory, the Moon is a single object formed in a giant collision between the ancient Earth and a small Mars-like planet. In simple words – scientists have thought that one massive object crashed into the Earth and sent a piece of huge rock into space that became the Moon.


New theory contradicts the commonly held “giant impact” paradigm in which one huge impact on ancient Earth caused the forming of single Moon-

Israeli scientists think that giant impact scenarios require very specific conditions such that they have a low probability of occurring. “Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth,” said co-author Prof. Perets. “It’s likely that such moonlets were later ejected, or collided with Earth or with each other to form bigger moons.”

In their study recently published in Nature Geoscience, the researchers explain that those moonlets, for over millions of years, have clumped together to create one, bigger Moon. The researchers conducted nearly 800 computer and numerical simulations, providing specific conditions.

In their scenario, each of many small collision forms a debris disk around the proto-Earth that then accretes to form a moonlet. The tidal forces from Earth cause moonlets to slowly migrate outwards. But their mutual gravitation attraction eventually causes the moonlets to affect each other, change their orbits and form the Earth’s satellite with its present characteristics. The moon is still receding from Earth today, at a pace of 1 cm a year.



The newly proposed theory suggests that the Moon we see every night is actually made of many smaller moons, or moonlets. Source:

Why does the Moon have the same chemical signature to Earth?

This theory of various collisions would explain why the Moon seems to be composed of material from Earth. None of the signs of foreign materials in the Moon aren’t yet found.

One possibility is that the object that crashed into the ancient Earth was made of exactly the same material as our planet. But Prof. Rufu, said that this scenario seems unlikely. “In contrast to the Earth and the Moon, meteorites and other material in the solar system vary substantially in their chemical signatures”, she explains.

Small collisions like this were common in the early solar system, and support their premise. But a London scientist not associated with the study, Imperial College’s Gareth Collins is urging more evidence on both sides of the moon-forming argument, Independent reports.

He says that it this theory could explain why the moon seems to have the same chemical signature to Earth. “It’s quite difficult, in one go, to get a lot of the Earth into orbit to form the moon. It can be done, but it requires very specific conditions which are rare, and you end up spinning the whole system a lot,” he said. “What’s nice about building the moon in stages is that some of the impacts can get stuff off the Earth and into orbit, and another set can set the Earth spinning.”

But, maybe the best answer will provide the Chinese’s sample return spacecraft, which will be launched next year. The spacecraft will collect lunar soil and rocks and return them back to Earth for analysis.

“If we had more lunar samples, that would be very helpful,” Rufu said. “One giant impact should produce a more homogenous rock, but under our scenario, I’d expect the composition to vary between different regions.”

Rufu and her colleagues agree that they still need to understand how moonlets might merge into one final moon. “As a scientist, you always have to ask ‘is it true or not?’ If you have too much confidence in your theory something is wrong,” she said.