Mars is a lifeless red desert with a thick, poisonous, orange atmosphere.
During the Heaven Wars, after the weapon Brave New World was defeated, one of its components was imprisoned on the obscure and secret planet of Mars. It was guarded by the last of the Faratin, the three colonies of Alpha, Sigma, and Theta. Eventually, Alpha left to request that Azmuth store them within the Omnitrix.
The other component of Brave New World, Dead London, was released from its prison on Cranvius and stole the Stardust to reach Mars. It breaks into Spirit of Man's tomb and merges with him. Timekiller and MALtruant offer it an alliance, but it refused and fights them off. It defeats Ben and Sigma before leaving to judge the Earth.