The moon was created following the collision of the Earth with a near-twin of our own planet, new
research has determined. Astronomers have long theorized that our companion satellite was formed from an encounter between the Earth and a planetary body roughly the size of Mars.

However, many questions remained, including the percentage of material from this primordial body still left in our natural satellite.  

Computer models suggest that the world that collided with the early Earth likely formed near our own world from similar materials.

Following the formation of the moon from debris, both bodies in the system were continually bombarded by smaller collisions from smaller protoplanets. This process resulted in a coating of material from these objects, with our own planet receiving a thicker deposit.

Theia, the name given to the impactor, likely collided with the Earth roughly 4.5 billion years ago. This body was roughly the size of Mars and possessed a mass roughly one-tenth that of the Earth. Computer models suggest that such an event would result in our satellite exhibiting a composition similar to that of the mantle of the Earth. Chemical and observational evidence of the lunar surface reveal the material seen on the moon is, in fact, largely the same as the mantle of our own planet.

Planets and large asteroids exhibit specific ratios between elements, which are determined by where they were formed in the solar system. Because the moon (and thus, Theia) was found to be chemically similar to the Earth's mantle, researchers believe the impactor formed in the same region of space as our home planet.

Isotopes are varieties of elements that contain identical numbers of protons, but differing quantities of neutrons. Ratios of isotopes can reveal significant information about astronomical bodies, including details of their formation. Although the physics of the impact between the Earth and Theia seemed to fit observational data, isotopic analysis did not seem to support the theory.

Relative levels of isotopes of tungsten in the Earth and the moon were examined by researchers, who found the planetary "fingerprints" to be largely similar. Most astronomers believed the moon would be different than our own planet, contain a higher concentration of tungsten-182. This was found in concentrations that suggest the material collected through minicollisions following the main impact.

"The problem is that Earth and the moon are very similar with respect to their isotopic fingerprints, suggesting that they are both ultimately formed from the same material that gathered early in the solar system's history. This is surprising, because the Mars-sized body that created the moon is expected to have been very different. So the conundrum is that Earth and the moon shouldn't be as similar as they are," Richard Walker of the University of Maryland said.

This new study shows the moon formed during an extremely violent period in the history of the solar system.

Analysis of isotopic ratios to determine the origin of the moon was profiled in the journal Nature.

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