Mondas

Mondas is the twin planet to Earth and is the home planet of the Cybermen, more specifically the Mondasian Cybermen. It drifted away from Earth's Solar System many years ago, Before the reformation of the League. The Mondasians had to adapt to deal with the conditions brought about by the lack of a star, and thus Cyberised their bodies and sealed themselves in tombs.

Mondas eventually found its own Star and was slingshotted back, sending it back towards Earth and reversing its thousand year journey. The Cybermen planned to return to our Solar System but eventually they looked to the stars instead, building massive starships and leaving the planet. Mondas now drifts through the Galaxy, lifeless, the Cybermen having abandoned it long ago. The remnants of the old cities built by the humanoids that lived on Monads can still be seen, as well as, if one looks hard enough, the ruined tombs of the Cyberised monsters that they became.

But there are legends from Mondas that go beyond the Cybermen. According to myths collected from spacers ad freighter pilots, Mondas is a world that rings with electronic screams, and that the planet itself is alive, shrieking at the monsters it nutured and what they have become. Caves filled with the bodies of prototype Cybermen, still barely alive, are rumoured to exist across the planet. And even worse than that, the planet itself is said to hold a darker secret, a metal heart incased at the very center that controls not just the Cybermen, but every piece of technology in the entire Galaxy.

But surely all that is just rumour, right?