So, yes, scientists have announced that there is likely a large body very far out in the solar system, hundreds of AU away. It obviously isn't official yet, but this is some very interesting news. The hypothetical planet would likely be about 10 times more massive than the Earth and would orbit about 20 times further away then Neptune. The evidence for the existence of this object, since we haven't actually seen anything, is that the orbits of 6 Kuiper Belt objects seem to be heavily influenced by something. The orbits all point in the same general direction, even though the objects, including the dwarf planet Sedna, are moving at very different speeds.
If you recall your astronomical history, you'll remember that the search for Neptune commenced because of perceived inconsistencies in Uranus' orbit, and that the search for Pluto occurred because of inconsistencies in Uranus' and Neptune's orbits. So, as with most extraordinary discoveries, it's important not to jump to any conclusions. But I do find it interesting that a few months back, scientists hypothesized the existence of a fifth gas giant in the early solar system which was cast out due to interactions from an early Jupiter or Saturn. This hypothetical planet would have been an ice giant, like Uranus and Neptune. The new "Ninth Planet" is also almost certainly an ice giant which probably did not form that far out in the solar system. Interesting how this works out, isn't it? I'm expecting to hear more about this in the future.
