Theia (THAY-uh) is the hypothetical planet that, according to the giant impact theory of the Moon's formation, collided with Earth over four billion years ago. This impact at a glancing angle would have destroyed Theia, its iron core burying itself within the primordial Earth. Volatiles in its mantle and surface would become massive quantities of ejecta thrown into orbit around Earth. From that material the Moon coalesced in a matter of no more than a century, possibly within less than a month. Earth would have gained significant amounts of angular momentum from such a collision, as well as an increase in total mass to its current level. Hypothetical planets are planets that have been suggested as possibly existing (or have been believed to exist), but have never been proven to actually exist. ... The Big Splash The giant impact theory (or Big Splash or Big Whack; cf. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... Earth is the third planet from the Sun. ... Earth cutaway from core to exosphere. ... In volcanology, ejecta consists of particles that came out of a volcanic vent, traveled though the air or under water, and fell back on the ground surface or on the ocean floor. ... In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ...

According to the theory, Theia would have been approximately Mars-sized and developed in the Earth-Sun L₄ position, similarly to Trojan asteroids. However, it would cease to be in a stable position due to its growing mass crossing the threshold at which it could no longer be considered negligible for a two-body Earth-Sun problem. It would begin to oscillate between approaching Earth and receding from Earth, before finally approaching close enough to fall along a path which would lead to a moderate-velocity impact (the glancing angle) with Earth. Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... The Lagrangian points (IPA: ; also Lagrange point, L-point, or libration point), are the five positions in space where a small object can be stationary with respect to two larger objects (such as a satellite with respect to the Earth and Moon). ... Image of the Trojan asteroids in front of and behind Jupiter along its orbital path. ...

In Greek mythology, Theia was a Titan who gave birth to the Moon goddess Selene. Greek mythology consists of an extensive collection of narratives detailing the lives and adventures of a wide variety of gods, goddesses, heroes, and heroines, which were first envisioned and disseminated in an oral-poetic tradition. ... In Greek mythology, Theia (also written Thea or Thia), also called Euryphaessa (wide-shining), was a Titan. ... For the moon of Saturn, see Titan (moon). ... Roman statue of the goddess Luna/Selene In Greek mythology, Selene (Σελήνη, moon) (the Roman moon goddess being Luna) was an ancient lunar deity, and the daughter of the Titans Hyperion and Theia. ...

Another name often given to this hypothetical planet is Orpheus. The head of Orpheus, from an 1865 painting by Gustave Moreau. ...