A study reveals an alternative to the origin of the Moon

A series of supercomputer simulations carried out by the University of Durham have revealed an alternative explanation for the origin of the Moon, which could have been formed thanks to a giant impact that immediately placed a body like the Moon in orbit of Earth roughly 4.5 billion years ago. Researchers at the Institute for Computational Cosmology at Durham University simulated hundreds of different impacts, varying the angle and speed of the collision, as well as the masses and spins of the two colliding bodies in their search of scenarios that could explain the current Earth-Moon system.

The theory is that the Moon formed after a collision 4.5 billion years ago between the young Earth and a Mars-sized object called Theia. Most theories create the Moon through the gradual accumulation of debris from this impact. However, this has been challenged by measurements of moon rocks which show that their composition is like that of the Earth’s mantle, while the impact produces debris that comes mainly from Theia.

If much of the Moon formed immediately after the giant impact, this could also mean that it melted less during formation than in standard theories, where the Moon grew within a debris disk around the earth. Depending on the details of subsequent solidification, these theories should predict different internal structures for the Moon.

The Moon, made with terrestrial material?

Calculations were performed using open source SWIFT simulation code, running on the DiRAC Memory Intensive Service (“COSMA”), hosted by Durham University on behalf of the DiRAC High Performance Computing Facility.

The additional computational power revealed that lower-resolution simulations can miss important aspects of large-scale collisions, allowing researchers to discover features that were not accessible to previous studies. Only high-resolution simulations produced the moon-like satellite, and the additional detail showed how its outer layers were richer in material from Earth.

Study co-author Vincent Eke said: “This formation pathway could help explain the similarity in isotopic composition between moon rocks returned by Apollo astronauts and Earth’s mantle. Also, there may be observable consequences for the thickness of the lunar crust, which would allow us to further pinpoint the type of collision that took place.”

Furthermore, they found that even when a satellite passes so close to Earth that it could be torn apart by the “tidal forces” of Earth’s gravity, the satellite can actually not only survive but also be pushed into an orbit that is wider and keeps it safe from future destruction.

“This opens up a whole new range of possible starting places for the Moon’s evolution. We went into this project not knowing exactly what the outcomes of these very high-resolution simulations would be. So, on top of the big eye-opener that standard resolutions can give you wrong answers, it was extra exciting that the new results could include a tantalisingly Moon-like satellite in orbit,” said lead researcher Jacob Kegerreis.