Planet Nine Might Be A "Rogue" Planet & Its Possible Existence Keeps Getting More Fascinating
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Here's your daily reminder that we occupy a tiny corner of the vast, ultimately unknowable universe. According to some scientists, Planet Nine might be a "rogue" planet captured by our solar system as it was zooming through space long ago. The most fascinating part? In all likelihood, there might be other Planet Nines traveling around the Milky Way.

For those whose hobbies don't involve falling into celestial Wikiholes, Planet Nine is a hypothetical world, approximately 10 times more massive than Earth, orbiting in the outer reaches of our solar system. I say "hypothetical" because researchers haven't managed to prove its existence just yet, but most say it's a matter of time before it's officially discovered. Most evidence for its existence comes from the erratic behavior of objects in the fringes of the system, whose orbits all appear to be influenced by something big. In fact, some researchers claim the planet might be responsible for the solar system's slight tilt in comparison to the Sun.

For most people, it's an exciting possibility because, well, there's a giant icy planet waiting to be found somewhere out beyond Pluto. For that certain brand of '90s kid, it's worth celebrating because we can finally have the nine planet solar system back — although Pluto's still not part of the club. Sorry.

On Tuesday, Space.com reported that a new study presented at a meeting of the American Astronomical Society offered a new explanation for how Planet Nine came to join our solar system. According to researchers, it's "very plausible" that the planet is a captured rogue — a world that traveled the universe solo until it was caught by our solar system. It sounds like the setup for a science fiction movie, but rogue planets actually outnumber planets that orbit a particular object.

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Working with a mentor, New Mexico State University undergraduate James Vesper ran a bunch of computer simulations of encounters between rogue planets and our solar system, changing factors like size and trajectory each time. Just over half the time, the rogue planet was flung out of the solar system and continued on its merry way. Every once in a while, it took a souvenir: at least one of the solar system's planets.

But 40 percent of the time, the rogue planet stuck around, caught orbiting the solar system. In a "soft capture," this addition didn't disturb any native planets, but sometimes, the rogue planet would send a native planet spinning off into the void.

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According to the simulations, we're unlikely to have ever encountered a rogue planet bigger than Neptune; if we had, the inner solar system would be rather more jumbled. This doesn't eliminate the possibility of Planet Nine, by the way — the planet may be bigger than Earth, but NASA suggests it's about the size of Neptune.

This is all based on simulations, of course, so the origins of Planet Nine aren't set in stone. For that matter, neither is its existence. The evidence of some sort of outer-system planet is strong, but until scientists officially detect it, Planet Nine remains purely hypothetical. Considering how people are already incorporating it into their doomsday predictions (for the record, this Planet Nine is not Nibiru), it's probably for the best that Planet Nine stays undiscovered until we Earthlings have time to get used to the idea.