Before we go any further, a caveat about Planet Nine: It's purely theoretical at this point. Batygin and Brown predict its existence based on unusual perturbations of the solar system that aren't otherwise easily explained. (This is the same technique scientists used to find Neptune.) But the history of astronomy is rife with speculations that never bear out: The same guy who correctly predicted the existence of Neptune also believed that a planet he called Vulcan was responsible for the wobble of Mercury. That "discovery" caused the astronomy world to waste years looking for something that wasn't there (Mercury's wobble was eventually explained by the theory of general relativity).