Moon created when 'about 20 moonlets collided'

Computer simulations examining thousands of scenarios have determined it would have taken about 20 mini-moons to create the one that orbits the Earth.

The researchers, from Israel, say the process may have taken millions of years.

It was previously believed that the moon was formed when a giant asteroid collided with the earth, knocking off a piece of it that ultimately failed to escape the Earth's gravity.

The scientists say the latest theory could explain why the moon appears to be made of material from Earth and not from outer space.

It was assumed that some of the asteroid would have remained attached to the piece that ended up in orbit.

1. A funfair ride in London the night before the supermoon
2. The scene over Whitby Abbey, in North Yorkshire
3. A plane flies past the moon in Nepal
4. A full moon behind a statue of Soviet state founder Vladimir Lenin on the eve of the supermoon in Kazakhstan
5. A British family watch the moon rise in Loughborough
6. The supermoon rises over the United States Capitol dome in Washington DC
7. The supermoon rising in Kansas City, Missouri
8. The supermoon rises over the Missouri River in North Dakota
9. An unusually large and bright moon adorns the night sky in Santiago, Chile
10. The supermoon rises over the Statue of Freedom on the Capitol dome in Washington DC
11. The moon rises behind clouds as the Emirates Air Line cable car is pictured in London's Docklands
12. Another image of the moon in London's Docklands

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The findings by Weizmann Institute of Science's Raluca Rufu were published in Nature Geoscience.

Co-author Hagai Perets of the Technion, Israel Institute of Technology in Haifa, said: "Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth.

Mr Rufu added: "It's likely that small moons formed through the process could cross orbits, collide and merge."

Gareth Collins, from London's Imperial College, said more evidence was needed in order to determine what happened.

In a companion article to accompany the theory, he said some of the moonlets must have been lost in space or failed to merge properly, so many more impacts may have been required.