Mars

Mars is the fourth planet from the Sun in the Sol System, just after Earth.

In the N.O.V.A. storyline
Various posters around the game, especially in Multiplayer maps. These depict Humans in the standard N.O.V.A. Military armour, and often an unknown insignia superimposed on the poster. It is unknown what kind of jobs were available on the Red Planet.

Around the time that Earth's crust was unable to further support humanity and the orbitals were built, Mars was colonised, and along with posters advertising the Near Orbitals during the final days of humanity's living on Earth, adverts offering work on Mars were also made. Mars is most likely the second planet to be inhabited by humanity, being both near to Earth and with a reasonably suitable temperature and atmosphere.

Trivia

 * The settlement shown in the first poster above is actually concept art for Boreas, outlining the similarities in environment.