A question about inhabitable planets

Hello all,
        In the process of constructing a new sphere I was struck with a question
that I couldn't see any answer in the 2e books  nor in the 3e stuff I have
access too.  How do you tell if a celestial body (Planet, moon, cluster,
belt, ect..) can sustain life?  I realize the roll of 'vacuum' disqualifies
a planet   but is there some chart or roll that I missed? Is it the
arbitrary decision of the DM?  I know that ultimately everything is the
whim of the Dm but if there's a method to be used to determine this I'd
certainly like to know.  Help would be appreciated.

         `Mike~