Outside the Lines: The Real ‘Planet X’

I blogged last week about the spectacular fanfiction that was the Star Trek/X-Men crossover novel 'Planet X,' but this New Scientist article about scientific mysteries shouts out the real Planet X -- or at least, the theory behind it. When you go past the (now non-planet) Pluto, space is littered with rocks from an asteroid belt until you reach what they call the Kupier cliff, where the rocks and debris suddenly disappear.

What caused it? The only answer seems to be a 10th planet. We're not talking about Quaoar or Sedna: this is a massive object, as big as Earth or Mars, that has swept the area clean of debris.

Although no one has ever actually seen Planet X, we can only assume that if it does exist, it is full of fictional characters from different universes interacting in unexpected and delightful ways.