Mars Mission is a Space theme that debuted in August 2007, and was officially discontinued by 2009. The theme focuses on the adventures of a team of Astronauts as they land on Mars and are forced to contend with a dangerous alien race.

The theme is often perceived as a spiritual successor to the previous Space theme, Life on Mars, although Life on Mars featured a peaceful Martians race rather than a war between humans and aliens.

The Astronauts
The humans are a group of astronauts that have journeyed to Mars in search of powerful yellow-green energy crystals found on the Martian surface. In the storyline, the humans are mining the crystals for a new source of energy, as Earth is experiencing an energy crisis. Unfortunately for the Astronauts, the Aliens are also seeking the crystals for themselves.

The human equipment, vehicles, and structures consist largely of two colours: bright orange and white. These two colours reflect harmful rays from Mars, which has no ozone to achieve ray deflection. They have the Classic Space symbol on their spacesuits. Tools used by the Astronauts include pickaxes, drills, Crysta-sensors, walkie-talkies, chainsaws and jackhammers, among others.

There are a range of Astronaut members in the Mars Mission theme, as well as additional characters in non-physical media. In Space Adventures - Mars Alien Attack, the Astronauts are led by a Commander. According to LEGO Battles, the Astronauts belong to a faction called Earth Command and are led by Commander Cold, who appears during cutscenes. The Astronauts' ground forces are led by Biff and Gemma.

The Aliens

The Aliens have originated from an unknown place in the cosmos, and are also searching for the crystals. In actuality, they are not from Mars, and are immediately identified as a dangerous and invasive force by the Astronauts. The Aliens themselves are transparent green and glow in the dark. Because the Aliens do not have tubes on the rear of their legs like normal minifigures, they have to be attached to their ships by their feet, using Erlings (studs on sides) elements. Alien Commanders are the leaders of the Alien army. The army attacks any human encampments and Astronauts that they encounter. The Aliens are shown to reside in underground hives. In 2008, it appeared that the Aliens had been routed, and the hives were destroyed.

According to LEGO Battles, there is an Alien Queen. The Alien Queen has the appearance of an Alien Commander, but her legs resemble those of Spy Clops from the Agents theme. There are also units from Exo-Force: Mini-Robots which fill the role of Builders, and Laser Troopers that are exactly like Devastators. Also, in LEGO Battles, the Aliens only wanted the crystals to power up their mothership to leave the planet.