Speaking of impactors, let’s talk about the Big One that occurred billions of years ago when a Mars-sized body hit the Earth and formed the Moon. The most recent understanding of this process is that an object scientists have named Theia collided with the early Earth about 4.5 billion years ago. The collision was but a graze or a flesh wound, ejected pieces of both bodies out into space, and then some pieces formed the Moon and the rest rejoined the proto-Earth.

Rocks taken from the Moon by the Apollo astronauts had similar compositions to rocks here on Earth, adding to the evidence that the two bodies shared bits and pieces after the collision. And the process was thought to have taken millennia to reach the current size and shape of the Earth-Moon system. However, in a new paper published in The Astrophysical Journal Letters and led by Jacob Kegerreis, supercomputer simulations found that the Moon was almost immediately placed into orbit around the Earth.

Study co-author Vincent Eke explains: 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.

At this point, we need more lunar samples to find more clues about the impact that led to the Moon’s creation, and from there, we can learn more about Earth’s history as well.

More Information

Durham University press release

Giant impact could have formed the Moon more rapidly, scientists reveal in new simulations (EurekAlert)

“Immediate Origin of the Moon as a Post-impact Satellite,” J. A. Kegerreis et al., 2022 October 4, The Astrophysical Journal Letters