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Astronomers from Penn State University trying to figure out the origin of our planet’s moon are now claiming that the moon was essentially stolen by the Earth.
The prevailing theory, known as the “Giant Impact Hypothesis,” has claimed that the moon was formed after a massive collision between Earth and the ancient planet Theia (which technically has never been proven to exist).
However, according to a new paper published in The Planetary Science Journal, a couple of astronomers now believe Earth’s gravity grabbed the moon out of space in what they are calling the “binary-exchange capture theory.”
The researchers, 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, stated in a press release, “In the alternative binary-exchange capture theory, the researchers said, Earth’s gravity separated the binary, snagging one of the objects — the moon — and making it a satellite that orbits in its current plane.”
In essence, the Earth stole the moon from another rocky space object using its gravity during a close encounter with it and our planet just kept it as its own.
The astronomers also point out that “a moon that forms from a planetary collision, taking shape as debris clumps together in a ring, should orbit above the planet’s equator. Earth’s moon orbits in a different plane.” They say its orbit is more in line with the sun than it is with the Earth’s equator, thus casting doubt on the “Giant Impact Hypothesis.”
Williams and Zugger determined that Earth could have captured a satellite even larger than the moon — an object the size of Mercury or even Mars — but the resulting orbit might not have been stable.
The problem is that the “capture” orbit — the one the moon follows — began as an elongated ellipse, rather than a circle. Over time, influenced by extreme tides, the shape of the orbit changed.
“Today, the Earth tide is ahead of the moon,” Williams said. “High tide accelerates the orbit. It gives it a pulse, a little bit of boost. Over time, the moon drifts a bit farther away.”
So now, according to their calculations, it is possible that “a binary-exchange captured satellite could behave as Earth’s moon does.”
As for how all of that happened?
“No one knows how the moon was formed,” Williams said. “For the last four decades, we have had one possibility for how it got there. Now, we have two. This opens a treasure trove of new questions and opportunities for further study.”
Now we just have to make sure someone doesn’t steal the moon from us!