Earth snatched Moon from space and did not birth it, study suggests

Pennsylvania

For nearly 40 years the Moon has been thought to be created by debris released when something collided with Earth. However, a new study offers another idea. What if this was not the case and the Moon was an external space body which Earth's gravity happened to catch?

The Apollo missions gave humans access to lunar soil. The astronauts who went to the moon between 1969 and 1972 collected more than 800 pounds of lunar rock and soil. 

An analysis found that they were similar in composition to what is found on Earth and that our satellite was birthed 60 million years after the solar system formed. Scientists gathered at the Kona Conference in 1984 and concluded that the Moon was formed by a collision with a young Earth. 

However, two Penn State researchers now say that it is likely the Moon was not born this way. The findings have been published in The Planetary Science Journal by Darren Williams, professor of astronomy and astrophysics at Penn State Behrend, and Michael Zugger, a senior research engineer at the Applied Research Lab at Penn State.

They say that the Moon was once part of a terrestrial binary. When it came too close to Earth, the planet caught one of them and repelled the other rocky object. 

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"The Kona Conference set the narrative for 40 years," Williams said. The authors added that this was not the end point and certain troubling points remained. 

Why Moon likely came from outside 

One of them is the position of the moon. They say that a moon formed due to a planetary collision and the debris clumping together in a ring should orbit above the planet's equator. However, our moon orbits in a different plane.

"The moon is more in line with the sun than it is with the Earth's equator," Williams said.

Providing their binary-exchange capture theory, the two of them believe Earth's gravity separated the binary and caught one of them. The one it snagged became our moon.

Citing another such instance in the solar system. Williams and Zugger point to Triton, Neptune's largest moon. Current studies say that Triton was pulled into orbit from the Kuiper Belt, where several binaries exist. 

They added that Moon's orbit started off as an elongated ellipse, rather than a circle. But extreme tides changed its shape over time. The researchers calculated tidal changes and the orbit's size and shape and determined our lunar satellite's orbit contracted over thousands of years and also became more circular.