A team of scientists from Zurich and the United States have reanalyzed moon samples from the Apollo missions and found that the Moon and Earth are even more similar in composition than thought.

The results help refine the giant impact model of the Moon's origins, making a case that the theorized Mars-sized object that smashed into Earth and created the Moon was a close neighbor of our planet.

Some scientists thought this object had come from outside the solar system.

The new findings, published in the Oct. 12 issue of the journal Science, are not revolutionary: Similar results were found soon after the lunar samples were obtained. But one of this study's scientists, Douglas Rumble from the Carnegie Institution, said these new results are ten times more precise. The precision could have found differences if there had been any.

The researchers found similarities between Earth and its satellite by studying the types of oxygen in samples of rock and soil from both. The Earth and Moon samples were found to contain the same ratios of certain oxygen isotopes. Isotopes are atoms of the same element that have slightly different masses.

"Oxygen isotopes are everywhere, they're pervasive," said Rumble. "Their ratios can and do vary around the universe, in fact by rather large amounts. Meteorites are all over the map whether they're from the asteroid belt or out in space."

(Meteorites are bits of space rock that make it down to Earth).

Because different isotopes result from exposure to varying radiation levels from the Sun or distant cosmic sources, substances with similar isotopic ratios mean they are from the same part of the universe.

Because of this simple rule, the scientist's findings support the idea that whatever hit the young Earth was a kind of sister planet, that orbited the Sun at roughly the same distance as Earth.

Intuitively, the Moon and Earth seem more dissimilar than these results show. For instance, no flora, fauna or atmosphere exists on our natural satellite.

One reason for this is that the Moon has no iron core. The diminutive density of the Moon has left it virtually without gravity, and therefore no atmosphere. The lack of iron is also explained by the giant impact: The top-most layers of Earth were thrown into orbit while heavy metals, mostly buried deep inside the young Earth, stayed here, making the Moon a lightweight.

Also, much of the gas and water that would have helped build a lunar atmosphere evaporated in the collision.

Despite the superficial differences between the two orbs, Lunar and Planetary scientist Paul Spudis says, "these findings only suggest that wherever the Moon came from, it came from close by."