Asteroid M is an asteroid converted by the mutant Magneto into his base that that floats a few miles above the Arctic Circle. Asteroid M serves as the training ground for the future protectors of mutantkind. Here, the most powerful mutants of this generation will train, and fully evolve their powers by a machine powered by a shard of the Ruby of Cyttorak. Asteroid M is further used as a giant superconductor that amplifies Magneto's electromagnetism over a thousandfold and allowing to finalize his plan to pulling a passing meteor shower directly towards Earth and bombard the planet in order to wipe out the human race and leaving mutantkind the sole survivors. Magneto's ally Doctor Doom used his magic in help cooling Asteroid M to sub-zero temperatures to achieve superconductivity.
Magneto brought Superman to Asteroid M and had him imprisoned there after being exposed to Kryptonite. The X-Men were also captured and brought to Asteroid M. Afterward fighting ensues that causes the destruction of the engines which keep Asteroid M at its high altitude, causing its impending crash on the surface below. To stop this, Superman, Cyclops and Havok use their powers to destroy Asteroid M before it can do any harm.