Pluto

Pluto was a dwarf-planet native to Earth's solar System. It's orbit around Sol was tilted instead of leveled like the other worlds due to the fact that it was a rogue moon of Neptune. In X = Ben + 2 the planetoid was destroyed by the Conquest Ray by Milleous to serve as an example of what will happen to Earth if Attea isn't returned.

Trivia

 * Matt Wayne hinted that Pluto probably will appear again in some point of the series.