A giant impact could have formed the Moon faster, scientists show in new simulations

Scientists at Durham University’s Institute for Computational Cosmology have used the most detailed supercomputer simulations to reveal an alternative explanation for the origin of the Moon, with a giant impact that immediately put the Moon-like body into orbit around Earth.

The researchers simulated hundreds of different impacts, varying the collision angle and speed, as well as the masses and spins of the two colliding bodies, in search of scenarios that could explain the current Earth-Moon system. These calculations were performed using SWIFT Open Code simulation code running on the DiRAC Memory Intensive (“COSMA”) service hosted by Durham University on behalf of the DiRAC High-Performance Computing facility.

The extra computing power has shown that lower-resolution simulations can miss important aspects of large-scale collisions, allowing researchers to spot features that were not available to previous studies. Only high-resolution simulations have created a moon-like moon, and the extra details have revealed how much richer its outer layers are in Earth-derived material.

If most of the Moon formed immediately after the giant impact, it could also mean that it was less molten during its formation than in standard theories where the Moon grew in a disk of debris around Earth. Depending on the details of the subsequent solidification, these theories should predict different internal structures of the Moon.

Study co-author Vincent Eke said: “This formation pathway may help explain the similarity in isotopic composition between Art lunar rocks returned by Apollo astronauts and Earth’s mantle. There may also be noticeable consequences for the thickness of the lunar crust, which will allow us to further determine the type of collision that occurred.”

In addition, they found that even when a satellite passes so close to Earth that it can be expected to be torn apart “tidal forces“from the earth’s gravity, the satellite can not only survive, but also be thrown into a wider orbit, protected from future destruction.

The study’s lead researcher, Jacob Kegerreis, said: “This opens up a whole range of possible starting points for the evolution of the Moon. We embarked on this project not knowing exactly what the results of these very high-resolution simulations would be. So, in addition to the fact that the standard permissions can give you the wrong answers, eye-opening, it was very interesting that the new results could include a moon-like satellite in orbit.”

The Moon is believed to have formed from a collision 4.5 billion years ago between the young Earth and a Mars-sized object called Theia. Most theories create the Moon by the gradual accumulation of debris from this impact. However, this has been disputed by measurements of lunar rocks, which have shown that their composition is similar to the Earth’s mantle, while the impact produced debris that came mainly from Theia.

This direct-satellite scenario opens up new possibilities for the original lunar orbit, as well as the predicted composition and internal structure of the Moon. A number of upcoming lunar missions should uncover new clues about what giant impact brought the moon, which in turn will tell us about the history of Earth itself.

The research team included scientists from NASA Research Center Ames and the University of Glasgow, UK, and their simulation results were published in Astrophysical Journal Letters.