Deimos

Deimos is the smaller and outermost of the two moons of the planet Mars. It is the scene of the second Doom episode, The Shores of Hell. "Deimos" is a Greek word which may be translated as "dread", "panic", or "terror".

Before the game, Deimos is teleported out of its orbit to float above Hell. (Interestingly, if Deimos were hollow and filled with air, it would be able to float in Venus' atmosphere like a helium balloon. (Like pretty much everything else.))