Brown, who has been dubbed the “Pluto Killer,” had already theorized that there is a so-called “Planet Nine” out there. This was based on his research on six bodies in the Kuiper Belt located beyond Neptune. And, in a series of recent tweets, Brown has hinted that there is a “new eccentric KBO,” or Kuiper Belt object, making a total of seven in that region. This seventh object, Brown adds, has a similarly peculiar orbit, which he believes is corroborating evidence that there is a Planet Nine in our solar system.
Existing theories suggest that Planet Nine was thrown off from its original orbit, and is now making an elliptical, “eccentric” orbit. This orbit, researchers believe, was about seven times further from our sun than Neptune, when it was at its shortest point. The elliptical orbit may take as many as 10,000 to 20,000 years to complete.
Meanwhile, another team of researchers claims there is a small chance Planet Nine was an exoplanet captured by the sun from a nearby star. As the sun was created in a relatively sizable stellar cluster with about 1,000 to 10,000 stars, it may have had some encounters with other stars, which may have resulted in some sort of planet-swapping, or, as Lick Observatory astronomer Greg Laughlin put it, “(picking) up an alien planet and (bringing) it along for the ride.”
Lead researcher Alexandar Mustill from Sweden’s Lund Observatory ran mock-ups of close encounters involving our solar system and others in the universe. And they discovered that if a solar system had a wide-orbit, or eccentric-orbit planet, that would give it a 50 percent greater chance of being captured by the sun. These odds, however, dropped considerably when Mustill and his colleagues considered whether passing systems would have planets with eccentric orbits, and that their simulations worked only if the sun captured a planet exactly like Planet Nine.
“Although these probabilities seem low, you have to compare them to each other, and not absolutely,” says Mustill, who now sees the odds of Planet Nine being an exoplanet at 0.1 to 2 percent. “Because ultimately any very specific outcome is very unlikely.”