Multiple studies address riddles of the Moon's origin
J Thoendell stashed this in Space
The problem is that most of what became the Moon should have come from the imposter - and based on our existing knowledge of what was flying where at that time, that imposter was thought to be a very different type of planet.
"So if the impactor had a different composition from the Earth, we should expect the Moon to have a different composition," Dr Hagai Perets, one of the study's authors, told the Nature podcast.
But this is not the case.
"They are almost identical. This is one of the major challenges for this really beautiful giant impact hypothesis," said Dr Perets, from the Technion-Israel Institute of Technology.
This is why a study made headlines in 2014 when it pinpointed some tiny differences between Earth and Moon rocks.
What Dr Perets and his colleagues found in their new simulations was that the impactor planet might, in fact, have been made of surprisingly similar stuff to the Earth - leaving only the sort of subtle differences that we do see in lunar material.
Sisters in space - how similar are the Earth and the Moon?
"What we found is that many of these impactors on a planet have very similar composition to that of the planets they impact - as similar as what we measure between the Earth and the Moon," Dr Perets explained.
Specifically, the models indicated a 20% chance that the impact could have been between such similar proto-planets.
These odds give our prevailing "origins story" for the Moon a fighting chance, Dr Perets said.
"[Now] I am even more confident about the giant impact hypothesis."