【History Archives】

Scientists have History Archivesgone back and forth about explanations for the moon's formation for decades, with the general consensus being that it formed during some type of cosmic collision between Earth and a Mars-sized space object about 4.5 billion years ago.

However, the exact type of impact continues to be hotly debated. Was it a slow, grazing swipe of Earth, or a massive collision that effectively vaporized early planet Earth?

A new study in the journal Natureon Monday lends credence to the idea that the moon was formed from the aftermath of a huge vaporizing collision involving Earth and another large object in space.

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The new study bases its conclusions in part on chemical analyses from seven moon samples astronauts brought back to Earth during the Apollo missions. The researchers measured the ratio of isotopes of potassium in the samples, and compared them to eight samples of Earth's mantle.

Original image has been replaced. Credit: Mashable

They found that the types of potassium isotopes measured on the moon and the Earth are slightly different.

Specifically, the chemical analysis detailed in the new study shows that the moon plays host to a heavier isotope of potassium in a higher ratio than the isotope is found on Earth.

This means that the Earth's mantle and the object that slammed into our early planet may have vaporized and mixed, allowing the moon to condense out of the huge, extraordinarily hot atmosphere created by the impact, according to the study.

The new research suggests that the heavier potassium would have condensed from the vaporized atmosphere created by the collision.

"Our results provide the first hard evidence that the impact really did (largely) vaporize Earth," co-author of the new study Kun Wang, said in a statement.

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Goes against low energy impact hypotheses

Original image has been replaced. Credit: Mashable

A slow, grazing impact could explain the moon's spin and the natural satellite's large size by comparison to our planet. However, the numerical models of that kind of impact also show that the moon should mostly be made of material delivered to this part of the solar system by whatever collided with it.

That hypothesis didn't necessarily work with what chemists have measured in moon rocks brought home by Apollo missions.

Recent studies now show that the isotopic composition of the moon and Earth are almost exactly the same when it comes to certain elements like oxygen.

It's possible that the space object that struck Earth would have had the same ratio of isotopes as the Earth, but that is extremely unlikely, as objects which form in other parts of the solar system should have different chemical makeups.

Some researchers seeking to understand the origin of the moon have favored the idea that the lunar body was formed from a relatively low-energy impact that would have produced a "silicate atmosphere," from which the moon would have formed, allowing it to have a similar chemical composition to Earth.

The new study, however, favors another idea entirely: That the moon was formed in a hugely hot atmosphere produced after a violent collision.

"I think it’s compelling work, and I think the preponderance of analysis points to a high-velocity impact," NASA's Noah Petro, who was unaffiliated with the new study, told Mashablein an interview.

"Now it's getting into the details of what happened."

Those details might become more clear as scientists continue to use new methods of analyzing moon rocks.

A team of researchers attempted to find a difference in the isotopic ratio of potassium on the Earth and the moon in 1995, according to Richard Walker, a professor of geology at the University of Maryland who is unaffiliated with this study, but found no difference between the two then.

The study published this week, however, made use of the bounty of moon rocks and new analytical techniques available more than 20 years later to effectively update that study and teach us even more about our moon.