Utopia

Asteroid M was Magneto's lair in orbit over the Earth. Destroyed, rebuilt & replaced various times; Asteroid M was destroyed in the sun & eventually fell to Earth after a conflict with the X-Men.

History
As the name implies, Asteroid M was an asteroid that orbited the Earth. It was primarily the home ofMagneto on several different occasions, and has repeatedly come under attack. It was a mostly composed of nickel and iron, which made it very susceptible to Magneto's magnetic powers. The asteroid also contained various life-supporting habitats on the surface and most likely underground as well. One frequently used tactic by Magneto was to suspend it within the Earth's atmosphere by magnetic levitation directly over any target he wished to intimidate.

Magneto often withdrew from regular human society, and took up residence on Asteroid M. At various times, it was also the home of Exodus and the other Acolytes, including the X-Man Colossus and the former New Mutants Rusty and Skids. However, it had been attacked and knocked out of orbit on different occasions. One such attack was the result of the Age of Apocalypse, when Holocaust first arrived in the Earth-616 universe he appeared on Asteroid M wantonly murdering and killing anyone who stood in his way.

There have been a few different versions of Asteroid M, although the concept was usually the same: to provide a safe secluded home for mutants. Sometimes Magneto was able to repair it through using his own magnetic powers. Other times he simply replaced it and started again on a new asteroid. It is yet unrevealed which version of Asteroid M was located on the floor of San Francisco Bay.Asteroid M was also used as part of Magneto's plans when he was disguised asXorn. When Cyclops, Wolverine & Fantomexinfiltrated Weapon Plus, they were sent into space. It wasn't until Magneto began to set his plans into motion that they realised the space station was really Asteroid M in disguise. Part of Magneto's plan was to destroy the trapped X-Men by sending Asteroid M crashing into the sun.

Utopia
Magneto (after regaining his mutant powers) flew to Utopia and offered to peacefully join the X-Men.Asteroid M had crashed down to Earth, and had seemingly been forgotten. However, the X-Men's specialist science team known as the X-Club located the remains of Asteroid M underwater in San Francisco Bay. Working in submarines and scuba apparatus they managed to repair the life support systems and turned the asteroid's technology into reclamation hardware. The asteroid was rocketed from the floor of San Francisco Bay up to the surface where it became an island in the middle of the bay. The X-Men took over the remains of Asteroid M and turned it into their new home, named Utopia. There, they offered all the remaining mutants and their families a home and a chance to live in peace, without fear of persecution.