Planemo Group

These are rogue planets, not bound to any star. Without any external source of heat, what happens to them is entirely based on whether they can retain or generate sufficient heat on their own, which mostly comes down to size.

They are divided into two classes, Endothermic and Exothermic.

These are worlds which are not massive enough to retain heat, so will be cold, dead worlds.

• Hauhetean - These have retained their hydrogen and helium atmospheres, but aren't massive enough for plate tectonics. They are generally smaller than 0.3 Earth masses.
• Nyxian - Too small to have retained their primary atmospheres. Generally smaller than 0.1 Earth masses.

• Kauketean - These are massive enough to have retained a thick atmosphere which traps internal heat. The surface is scorching hot.
• Odyssian - These are massive enough to be considered Jovian worlds if they were in orbit around a star.
• Stevensonian -These are Planemo worlds most likely to be habitable. A thick atmosphere traps geothermal heat, allowing for liquid water oceans. The lack of solar heating means that the temperatures are similar all across the world.