The GM's Planet-Building Handbook

From publisher blurb:

So, your sci-fi RPG campaign is going to span vast volumes of space and introduce new alien races from an exotic medley of planets. But just what are those planets like? This handbook will allow you to design realistic planets capable of bearing human (or human-like) life. Guidance is given on:

Host star
Planet orbit
Planet size
Axial tilt
Moons
Planet rotation
Magnetosphere
Geological activity
Atmosphere
Hydrosphere
Climate

Plus, there's a section on how to produce accurate maps of your planet.

The handbook is based on scientific principles, but don't worry, all the numbers have been crunched and distilled to a few easy-to-use charts and tables.