 Two scientists claim that they have found the best evidence yet that a huge ninth planet exists at the outer limits of the solar system. It's called Planet X, and it's about 10 times the mass of Earth, or roughly the size of Neptune. The planet supposedly orbits far out from the Sun on a highly elliptical path, which takes 10 to 20,000 years to make one full circuit. And it's way out there, too, somewhere between 200 and 1,200 times the distance from the Sun to Earth. But don't get too excited yet. No one has actually seen this planet. The entire argument about its existence is theoretical. It's based on the observations of six objects in the Kuiper Belt, the large cloud of icy bodies at the edge of the solar system. The way these objects move around the Sun seems to indicate that they're being affected by something big, aka Planet X. That's about all the evidence we have, though, and some experts think that six objects is a pretty low sample size for such a big claim. Also, the researchers say that the probability of this all being a coincidence is 1 in 150,000. Those are pretty good odds, but usually scientists like to have a way lower probability of failure, around 1 in 1.7 million. Still, experts agree that the models supporting Planet X are strong, and we've used this indirect method to find planets before. Neptune was originally detected by observing anomalies in the movement of Uranus. Plus, having a huge planet like this so far out from the Sun isn't exactly out of the ordinary. Planets of this size are very common throughout the universe, so Planet X would make our solar system much more normal than strange. Now all we've got to do is find it. The Large Synoptic Survey Telescope in Chile or the Subaru Telescope in Hawaii may be sensitive to pick it up, but until this long-lost world is actually found, it's really only an exciting theory.