The energy of such a giant impact is predicted to have heated Earth to produce a global magma ocean, and evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle has been documented. However, there remain several questions concerning the best current models of the giant-impact hypothesis.

The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin.

Giant collisions are consistent with the leading theory of the formation of the Solar System.

There is evidence in other star systems of similar collisions, resulting in debris discs.

Vaporizing at comparably lower temperatures, they could be lost in a high-energy event, with the Moon's smaller gravity unable to recapture them while Earth did.

The Moon is depleted in volatile elements compared to Earth.

This would leave the Moon with less metallic iron than other planetary bodies. Computer models of a giant impact of a Mars-sized body with Earth indicate the impactor's core would likely penetrate Earth and fuse with its own core. This gives the Moon a lower density than Earth.

The Moon has a relatively small iron core.

An extremely energetic process, such as a giant impact, could provide this energy. This may have required more energy than predicted to be available from the accretion of a body of the Moon's size.

Moon samples indicate that the Moon was once molten down to a substantial, but unknown, depth.

A giant impact may have supplied this excess momentum. Meaning, the momentum contained in Earth's rotation, the Moon's rotation, and the Moon revolving around Earth is significantly higher than the other terrestrial planets.

The EarthвЂ“Moon system contains an anomalously high angular momentum.

Earth's spin and the Moon's orbit have similar orientations.

The giant-impact hypothesis is currently the favored scientific hypothesis for the formation of the Moon. Analysis of lunar rocks, published in a 2016 report, suggests that the impact may have been a direct hit, causing a thorough mixing of both parent bodies. The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon. The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean eon (about 20 to 100 million years after the Solar System coalesced). Such an impact between Earth and a Mars-sized object likely formed the Moon. Artist's depiction of a collision between two planetary bodies.

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