There are all kinds of conspiracy theories about Planet X: a planet that supposedly lurks at the edge of our solar system, that it's as big as Jupiter and that NASA is concealing it because it's on a collision course with Earth. Though it's not quite that big, or out to kill us, or at all familiar to a select few with a high security clearance, evidence that a planet does exist beyond Pluto is mounting.
Richard A. Lovett recently covered the new evidence in Cosmos magazine. Lovett explains that evidence for Planet X exists in simulations that show that Pluto's large moon Charon, wasn't always orbiting the dwarf planet. At some point in cosmic history the two bodies may have gently collided, after which Charon became entwined in Pluto's gravity. New Horizon's principle investigator Alan Stern thinks that such a collision probably means that Pluto and Charon have company. Lovett writes:
The outer Solar System is enormous. If Pluto and Charon were the only large objects out there, the chances of them colliding would have been minute. Stern has calculated it would take 10,000 times the age of the entire Universe for any collision between a lonely Pluto and Charon to become likely. But if you had “1,000 Pluto-sized objects” in the region, then the meeting becomes more probable said Stern at a meeting last year of the American Geophysical Union in San Francisco.
“We might even find Mars and Earth-sized things,” Stern tells Lovett.
Scientists already know that there are more dwarf planets beyond Pluto. Last year, Scott Sheppard, an astronomer at the Carnegie Institution for Science, announced that he had found a small planetary body he named "Biden." Biden and it's fellow small icy bodies orbit in a pattern that's tell-tale of planet's gravitational influence, suggesting that there might be larger worlds out there, waiting to be discovered.