Yesterday's discovery of 2012 VP113, very likely the fifth dwarf planet in our solar system, was important in its own right. But it now seems quite possible that there's something much, much larger out there that has influenced its orbit—a very large object that we can't see and know nothing about.
2012 VP113's 4,000-year orbit never brings it anywhere near the Sun—at its closest it's 12 billion miles away, more than three times the average distance between the Sun and Pluto. It's way out there, as this animation from Clark Planetarium shows:
There are several working hypotheses that might explain why the orbit is so erratic. One possible explanation is that a massive celestial object has pulled, or is currently pulling, VP113 into its unusual trajectory. If it is a planet, we can be reasonably sure that it's smaller than Saturn—anything that big would have caught the attention of NASA's Wide-Field Infrared Survey Explorer (WISE) telescope—but we can also be reasonably sure that it's significantly larger than Earth. Since Saturn's mass is 95.16 times that of Earth, that leaves a pretty wide range. (Some scientists have dubbed this unknown planet a "super-Earth," but all that means is that they expect it to be larger than Earth.) If the planet has an extremely long and elliptical orbit, or has been ejected from the solar system entirely, we're going to have a hard time finding it—but if we do, we'll have a full-fledged ninth planet in our solar system to replace the recently-demoted Pluto.