Supercomputer simulation suggests alternative theory for Moon’s creation

Currently, the most widely accepted origin theory for the Moon posits that it was formed 4.51 billion years ago, not long after the Earth, out of the debris from a giant impact between the planet and a hypothesised Mars-sized body called Theia.

Most theories create the Moon by gradual accumulation of the debris from this impact. However, this has been challenged by measurements of lunar rocks showing their composition is like that of Earth’s mantle.

A team from 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 for scenarios that could explain the present-day Earth-Moon system.

These calculations were performed using the SWIFT open-source simulation code, run on the DiRAC Memory Intensive service, hosted by Durham University.

The extra computational power revealed that lower-resolution simulations can miss out on important aspects of large-scale collisions. Only the high-resolution simulations produced the Moon-like satellite, and the extra detail showed how its outer layers were richer in material originating from the Earth.

If much of the Moon formed immediately following the giant impact, then this could also mean that less of it became molten during formation than in the standard theories where the Moon grew within a debris disc around Earth.

Depending upon how this molten mass later solidified, the simulation suggests that the Moon could have different internal structures from what was previously believed.

Co-author of the study Vincent Eke said: “This formation route could help explain the similarity in isotopic composition between the lunar rocks returned by the Apollo astronauts and Earth’s mantle. There may also be observable consequences for the thickness of the lunar crust, which would allow us to pin down further the type of collision that took place.”

Furthermore, they found that even when a satellite passes so close to the Earth that it might be expected to be torn apart by the ‘tidal forces’ from Earth’s gravity, the satellite actually can not only survive but also be pushed onto a wider orbit, safe from future destruction.

The lead researcher of the study, Jacob Kegerreis, said: “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.”

With numerous lunar missions planned for the near future, new clues about what kind of giant impact led to the Moon may be uncovered.