Excellent book, it is short and to the point !
This is not a set of tables to randomly generate worlds, we have this in many sf games anyways.
This guide explains you how do planet "work", what is the physic and the logic in their features, climates, etc. It is not too technical and it is very easy to read.
Once you have read this book you won't be looking at rpg planets the same way anymore. A MUST READ before going into planet design.
[5 of 5 Stars!]