Mars is the fourth of the many planets.
Mars is the fourth planet from the sun located within Earth's solar system.
Generation One animated series
The Earth Defense Command has a base operating on Mars.
The Headmasters anime
Having harnessed the plasma energy released when the Transformers' homeworld of Cybertron was destroyed, Decepticon Headmaster leader Scorponok sought to generate and collect more of the energy to fuel his ambitions. To accomplish this, Scorponok plotted the destruction of Mars, and ordered the Terrorcons to plant plasma energy bombs beneath the surface of the planet Mars at strategic points which would, when detonated, rip the planet apart.
The Decepticons' activities were discovered by Spike, Daniel, Wheelie and the Trainbots, who were on Mars conducting a geological survey at the time. The Autobot Headmasters were called in to deal with the threat, but during the battle that ensued, Fortress Maximus was de-powered by a plasma energy blast. Scorponok took the opportunity to activate his newly constructed Transtector and travel to Mars where he pummeled Maximus before ordering the planet's destruction. Two clusters of bombs placed at the Martian planetary poles were detonated simultaneously by Soundblaster, beginning a chain reaction that started to tear Mars apart. Scorponok and the Decepticons evacuated while the Autobots were consumed by the inferno, but Fortress Maximus was able to absorb some of the energy released in the early stages of the conflagration and made his escape as Mars exploded.
Incredibly, the destruction of Mars had a minimal impact on the various planetary orbits throughout the Sol system, and the fate of its moon was not divulged, but its absence did disrupt the gravimetric balance of space bridge travel, destabilizing it.
Ore acquired from Mars, coupled with ores from Earth and other planets, was used in the creation of Schaeffer Energy. Jean Minakaze happened to be visiting the Schaeffer Energy plant in America as a cargo ship carrying a payload of Martian ore returned from its space mission.
Jetfire and Starscream once travelled to Mars in seach of the Mini-Con panel containing Firebot. Upon hearing this, the kids asked the two Transformers to buy them something from the souvenir shop. Sadly, as Mars was uninhabited by either human or alien lifeforms, there were no shops to be found. Starscream did however find a mysterious glowing green rock and gave it to the children. They were so happy.
Joke's on them - its probably radioactive.
Ten years after the defeat of Unicron, the Cybertronian Alliance and the Earth Federation installed a facility on the surface of Mars to mine the potent naturally-occuring ore Energon. Unfortunately, this facility was decimated by the initial Terrorcon attack, leading Carlos to aptly remark "Holy frijoles".
Thunderblast, Ransack, Crumplezone and Thundercracker left Earth on a rickety rocket, attempting to forge the New Decepticon Army. Their rocket made it as far as Mars before crashing and stranding them on the planet.
During the 2007 TF live-action film, there is a scene on the Martian surface in which an indistinct Transformer destroys the Beagle 2 Rover. This scene was also incorporated into early teaser trailers for the movie.