Giant impact hypothesis#Theia

Theia is the unofficial name of a hypothetical proto planet that collided, according to the collision theory of lunar origin about 4.5 billion years ago with the proto- Earth. Theia itself was destroyed in the collision; products formed during impact fragments have been collected in an orbit around the Earth. In the course of it the moon has formed. According to this theory Theia was about the size of Mars and was formed by one of the models as Trojans in the L4 Lagrange point of the Sun-Earth system before it collided with the Earth.

Name

The name Theia for the hypothetical planet was first used in a paper from the year 2000 ( AN Halliday ) and comes from the Greek mythology. Theia was a Titan who gave birth to the moon goddess Selene.

Formation

From a comparison of isotopes in terrestrial and lunar rocks could be deduced that most of the material from which was formed the moon, the mantle of the proto- Earth comes from. The material Theias obviously caused no change in the isotopic composition of the proto- Earth. This fact can be interpreted in different ways. Either the protoplanet was at the same distance from the Sun as the proto earth and because of the large sun near the protoplanet sat for the most part composed of silicates, or Theia consisted primarily of ice.

The theory that Theia has arisen in the L4 Lagrangian point of the Sun-Earth system, speaks for that possibility. Recent simulations involving the chaotic effects of motion in the vicinity of Lagrange show that a body is formed in L4 can actually achieve the required speed, to make the Moon formed.