The Moon is believed to have formed from a collision, 4.5 billion years ago, between Earth and another planet the size of Mars, called “Theia.”
Scientists have simulated this process and reproduced many of the properties of the Earth-Moon system. However, there is a problem. The Moon appears to be made up of material that would not be expected if the current collision theory is correct, this is called the Lunar Paradox.
According to current theories and the analyses of the various simulations of the Earth-Theia collision predict that the Moon is mostly made up of material from Theia. However, studying materials from both Earth and the Moon, shows remarkable similarities. In fact, elements found on the Moon show identical isotopic properties to those found on Earth.
This is unlikely because that would mean that both Theia and Earth had identical isotopic compositions, which is pretty much impossible, or at the very least improbable.
A group of researchers from the University of Bern, Switzerland, have proposed a solution to the Lunar Paradox. The researchers used different geometries for possible collisions than previously others had simulated. They also used new impacts configurations. Some of these are the so-called, “hit-and-run collisions,” where a significant amount of material is lost into space on orbits unbound to Earth (i.e. the material fly’s off into space).