Topaz is the only moon orbiting Tholia. It sports a very thin and dusty atmosphere. This atmosphere does little to regulate the temperature of this moon, however. On one side of the planet, the atmosphere freezes and bonds with rocks on the surface. On the other (sunward) side, great fountains of gas spew from the surface and rain back on the surface in giant umbrella-like plumes, just barely captured by the light gravity here.

This moon bears few signs of humanoid occupation. Some structures are visible in the middle latitudes, but they are small enough to indicate that they are subterranean. Sensors indicate that large-scale mining operations may once have been carried out on this planet, though this is only an estimation. Those who did initiate such an operation were careful to follow the natural crevices and lava tubes of Topaz's interior. The degree to which care was taken to follow the natural lay of the land seems almost counter-productive from a mining standpoint.