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Moon mystery could be solved by simulation of planetary smash-up

The moon is thought to have been created in a violent collision, and a new simulation of the event could answer questions that have puzzled astrophysicists

By Alex Wilkins

11 March 2022

Artwork of the young Earth-Moon system. The Earth had recently formed when it was struck by a protoplanet called Theia roughly three times the size of Mars. Debris from the impact went into orbit, while the cores of the two planets merged. Within weeks of the event, the debris formed a Saturn-like ring around the Earth. Later collisions in this ring led to the formation of the Moon, probably within just a few thousand years. Initially the Earth and Moon were much closer together than they are now, and spinning more quickly.

Artwork of the collision that gave rise to the moon

MARK GARLICK/SCIENCE PHOTO LIBRARY

A computer simulation that traces the moon’s formation in high resolution may explain the mystery of why it is so chemically similar to Earth.

The conventional story for the moon’s origin is that a primordial planet named Theia smashed into Earth and spewed molten rock into space. This debris, primarily made up of Theia, then coalesced into the moon over tens of millions of years.

While this scenario accounts the moon’s observed angular momentum, it fails to explain the…

Article amended on 16 March 2022

We clarified how many particles the model simulated.

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