The Giant Impact Hypothesis
The Giant Impact Hypothesis suggests that the formation of Moon was due to a cataclysmic collision between Earth and a Mars sized planet- Thea approximately 4.5 billion years ago i.e. about 20-100 million years after the formation of our Solar System. The colliding body, Thea, is named after a mythical Greek Titan who was the Mother of Selene, the Goddess of Moon.
Over the our Moon has troubled scientists with its mysterious origin. There have been many theories/hypotheses explaining the weird birth of our celestial neighbor. Of all the hypotheses the Giant Impact Hypothesis is able to explain all the mysteries of our Earth-Moon system.
As of 2001 the giant impact hypothesis is the favoured scientific hypothesis for the formation of the Moon. Supporting evidences includes:
Earth's spin and the Moon's orbit have similar orientations.
Moon samples indicate that the Moon once had a molten surface.
The Moon has a relatively small iron core.
The Moon has a lower density than Earth.
Evidence exists of similar collisions in other star systems (that result in debris disks).
Giant collisions are consistent with the leading theories of the formation of the solar system.
The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin.
The energy of such a giant impact is predicted to have heated the Earth to produce a giant "ocean" of magma covering all of the Earth's crust, yet there is no evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle. As of 2015 there is no self-consistent model that starts with the giant-impact event and follows the evolution of the debris into a single moon. Other remaining questions include when the Moon lost its share of volatile elements and why Venus - which experienced giant impacts during its formation - does not host a similar moon.
