Titan

Titan was the largest moon of the planet Saturn in the Sol system. The atmosphere of Titan was toxic to Humans and could be used for special starship maneuvers. 

In the 2140s, while on Titan as part of the Omega training mission with Captain Jonathan Archer, Trip Tucker encountered problems while on an extra vehicular (EV) exercise. His EV pack froze up and he experienced nitrogen narcosis. However, Archer was able to convince Trip not to remove his helmet while still unsheltered on Titan's surface. 

Titan was a major navigational reference within Saturn's planetary system. Nova Squadron used Titan as a rendezvous point before beginning training maneuvers during preparations for Starfleet Academy's commencement exercises in 2368. 

Titan was also a favored way point for pilots making the Jovian Run. A dangerous shuttlecraft maneuver sometimes performed by Starfleet pilots on this run was called Titan's Turn. 

In an alternate reality, the crew of the USS Enterprise (alternate reality) used the conditions on Saturn and Titan to help hide their ship from the sensors of the Narada.