Planet X

Planet X is a world which appears in Toho Company’s Godzilla franchise.

Description
A barren, rocky planet which appears to occupy an orbital path very close to that of the gas giant Jupiter, Planet X is home to the alien Xiliens. It would seem to be roughly the same size as Earth as the gravity on the surface is very similar to that experienced here. Planet X possesses an atmosphere of some description, as the Xilians, King Ghidorah and Rodan are all capable of surviving on the surface without the assistance of breathing apparatus, although human astronauts still needed to wear their EVA suits whilst visiting.

The cities of the Xiliens are never shown, although given the bleak nature of the planet‘s surface and its proximity to Jupiter, it is entirely possible that they are all built underground.

History
When the Xiliens approached humanity to ask to borrow the monsters Godzilla and Rodan to drive the “marauding” King Ghidorah from their homeworld, the humans agreed, and the pair were transported to Planet X to do battle. This was all later discovered to be a ruse by the Xiliens to gain control of the monsters, and the Xiliens quickly returned all three kaiju to Earth for their invasion attempt.

Trivia

 * Planet X is to date the only non-terrestrial location visited by Godzilla in any of his appearances.