Apollo rocks brought to the Earth by astronauts four decades ago are lending new evidence to the theory the moon was created by a collision between the Earth and a Mars-sized body. The samples were returned from the Apollo 11 and 12 missions, launched in 1969, and Apollo 16, which went to the moon in 1972. 

This planetary object, Theia, is believed to have subjected Earth to a glancing blow during a collision 4.5 billion years ago. Most astrophysicists believe this impact raised large quantities of debris into orbit around the Earth. For a short time, based on this theory, our home planet had a ring system, something like those around the gas giants today. Over time, it is believed this debris coalesced into the moon we see in the sky today. 

Using a new method of chemical analysis, German researchers were able to determine the rocks obtained from the lunar surface had a slightly different composition than would be expected of terrestrial samples. 

Elements each have a specific number of protons in their nucleus, which determines the identity of the atom. Atoms with eight of these positively-charged particles are what we call oxygen. Also in the nucleus are uncharged neutrons, which can vary in number. Oxygen can possess anywhere from eight (oxygen-16) to 10 (oxygen-18) of these particles in stable form. When two atoms of the same element have different numbers of neutrons, they are called isotopes. It is a difference in these oxygen isotopes that were detected in this new research. 

This could suggest the rocks, and hence the moon, is partially composed of material from Theia. Early analysis indicates the composition of the lunar surface is composed of nearly identical amounts of material from the Earth and Theia. 

"We have developed a technique that guarantees perfect separation [of oxygen isotopes from other trace gases]. The differences are small and difficult to detect, but they are there," Daniel Herwartz of the University of Cologne in Germany, stated to Reuters. 

This is the first study to show a difference in isotopes between rocks from the moon and Earth. 

"[T]he lunar samples had an O-17 to O-16 ratio that was 12 parts per million higher than rocks derived from Earth's mantle," researchers wrote in the article announcing their findings.

However, because the differences are so slight, debate is likely to rage among scientists over whether or not the findings constitute proof of the collision. 

Analysis of the Apollo rocks and oxygen isotope evidence of an impact between Earth and Theia was published in the journal Science.