Pluto was a dwarf planet orbiting the Sun as a large member of the Kuiper Belt. In the PlanetSide 2 timeline, Pluto was mysteriously destroyed in 2444, during the destabilization and closing of a wormhole that had appeared several weeks earlier. Its fragments apparently became lost among the other rock and ice formations of the Kuiper Belt and remained so until they were rediscovered by Tom Connery in 2615.
While the ultimate cause of Pluto’s destruction is unknown, the event sparked panics that it was the result of an extra-terrestrial super weapon, fired through the rift in an attempt to hit Earth. It wasn’t until the same wormhole reopened and closed without similar incident 98.3 years later that this commonly-held belief was largely extinguished and space exploration in the Sol system resumed in earnest. Similar speculations did occur, however, when an alien artifact was discovered in the Kuiper Belt in 2630.