Editing Giant-impact hypothesis (section)

== Possible origin of Theia ==
[[Image: BigSplashEnglish.svg|thumb|One suggested pathway for the impact as viewed from the direction of Earth's south pole (not to scale).]]
In 2004, [[Princeton University]] mathematician [[Edward Belbruno]] and astrophysicist [[J. Richard Gott III]] proposed that Theia coalesced at the {{L4}} or {{L5}} [[Lagrangian point]] relative to Earth (in about the same orbit and about 60° ahead or behind),<ref name=belbruno-2005/><ref name=mps40_1115/> similar to a [[trojan asteroid]].<ref name=mackenzie03/> Two-dimensional computer models suggest that the stability of Theia's proposed [[Trojan (astronomy)|trojan orbit]] would have been affected when its growing mass exceeded a threshold of approximately 10% of Earth's mass (the mass of Mars).<ref name=belbruno-2005/> In this scenario, gravitational perturbations by [[planetesimal]]s caused Theia to depart from its stable Lagrangian location, and subsequent interactions with proto-Earth led to a collision between the two bodies.<ref name=belbruno-2005/>

In 2008, evidence was presented that suggests that the collision might have occurred later than the accepted value of 4.53&nbsp;[[Gya (unit)|Gya]], at approximately 4.48&nbsp;Gya.<ref name=halliday-2008/> A 2014 comparison of computer simulations with elemental abundance measurements in Earth's mantle indicated that the collision occurred approximately 95&nbsp;My after the formation of the Solar System.<ref name=jacobson-2014/>

It has been suggested that other significant objects might have been created by the impact, which could have remained in orbit between Earth and the Moon, stuck in Lagrangian points. Such objects might have stayed within the Earth–Moon system for as long as 100 million years, until the gravitational tugs of other planets destabilised the system enough to free the objects.<ref name=ns080506/> A study published in 2011 suggested that a subsequent collision between the Moon and one of these smaller bodies caused the notable differences in physical characteristics between the two hemispheres of the Moon.<ref name=nature476_69/> This collision, simulations have supported, would have been at a low enough velocity so as not to form a crater; instead, the material from the smaller body would have spread out across the Moon (in what would become its [[Far side of the Moon|far side]]), adding a thick layer of highlands crust.<ref name=yahoo20110803/> The resulting mass irregularities would subsequently produce a gravity gradient that resulted in [[tidal locking]] of the Moon so that today, only the near side remains visible from Earth. However, mapping by the [[Gravity Recovery and Interior Laboratory|GRAIL]] mission has ruled out this scenario.{{citation needed|date=December 2013}}

In 2019, a team at the [[University of Münster]] reported that the [[molybdenum]] isotopic composition in Earth's primitive mantle originates from the outer Solar System, hinting at the source of water on Earth. One possible explanation is that Theia originated in the outer Solar System.<ref>{{Cite journal|last1=Budde|first1=Gerrit|last2=Burkhardt|first2=Christoph|last3=Kleine|first3=Thorsten|date=2019-05-20|title=Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth|journal=Nature Astronomy|volume=3|issue=8|pages=736–741|language=en|doi=10.1038/s41550-019-0779-y|issn=2397-3366|bibcode=2019NatAs...3..736B|s2cid=181460133}}</ref>