World Library  
Flag as Inappropriate
Email this Article

Theia (planet)


Theia (planet)

Artist's depiction of a collision between two planetary bodies similar to the hypothesized proto-Earth and the smaller, Mars sized protoplanet - Theia.

Theia is a hypothesized ancient planetary-mass object in the early Solar System that according to the giant impact hypothesis collided with the Early Earth around 4.533 billion years ago (BYa).[1] According to the hypothesis, Theia was an Earth trojan about the size of Mars; if the impact were not glancing, it could have destroyed Earth. Models of the impact propose that Theia's debris gathered together around Earth to form what was the early Moon. After the debris from the collision flew into space, some scientists think that it originally formed two moons[2][3] which later merged to form the single Moon we know today. However, the two-moon hypothesis is not necessary to explain the difference in the faces of the near and far sides of the Moon. The theory also explains the reason that Earth's core is larger than it would be for a body its size, since according to the theory, Theia's core merged with Earth's.[4]


  • Orbit 1
  • Name 2
  • Collision 3
  • Theories 4
  • References 5


Theia was thought to have orbited in the L4 or L5 spots in the Earth's orbit. It grew to a Mars-like size and, through gravitational perturbation from Venus, was moved around and eventually set on a collision course with Earth.[5]


The name for Theia came from the Greek titaness, Theia. In mythology, Theia was the mother of Selene, the goddess of the moon, just as the planet Theia's collision with the early Earth is theorized to have created the Moon. An alternative name, Orpheus, has been used in the past but has largely been discarded.


According to the Giant Impact Hypothesis Theia orbited the Sun at around the orbit of Earth at the L4 or L5 Lagrangian points, but was perturbed by Jupiter and Venus into a collision with the proto-Earth. Theia struck Earth with a glancing blow[6] and ejected many pieces of both the proto-Earth and Theia. These pieces either formed one body that became the Moon, or formed two moons that eventually merged to form the Moon.[2] Had Theia struck the proto-Earth head-on, it would have led to the destruction of both planets, creating a short-lived asteroid belt between the orbits of Venus and Mars.


From the beginning of modern astronomy, there have been at least four hypotheses for the proposed origin of the Moon: that a single body somehow divided into Earth and Moon; that the Moon was captured by Earth's gravity (as most of the outer planets' smaller moons were captured); that Earth and Moon formed at the same time when the protoplanetary disk accreted; and the Theia scenario. The lunar rock samples retrieved by Apollo astronauts were found to be very similar in composition to Earth's crust, and so were likely removed from Earth in some violent event.[7][8]


  1. ^
  2. ^ a b
  3. ^ "Faceoff! The Moon's oddly different sides", Astronomy, August 2014, 44-49.
  4. ^ A New Model for the Origin of the Moon
  5. ^
  6. ^
  7. ^
  8. ^
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.