First appereance: Beyond The Impossible #212
Known facts: the planet orbited a blue supergiant star and was tidally locked, making life on the surface unsustainable.
SPOILER WARNING: Plot details after Beyond The Impossible #220
The Dragon Tomb was an artificially created planet in the Olympian Galaxy, located in the Omoroca star system in the Enyo sector.
Tiamat was imprisoned there for a billion years thanks to the Drylon device called the Time Mover. She was later freed by Eris , destroying the planet in the process.
The entire solar system was annihilated when Tiamat was defeated and became part of the Dead Zone.