Ditto to GURPS Space.
I mocked up some 2300 stuff ala Constantine with Astrosynthesis. There's a plug-in for GURPS Space characteristics. So you can convert everything over and get a long view of what the planet is like. It looks good and you can store the original data (actual gas composition) etc.
Sure, we could get extremely into every aspect of it but there does need to be some hand-waving. General idea of atmosphere, possible unique factors and extrapolations to weather, climate and biology/botany. Gurps Space does a great job of laying these out with suggestions for life on various planets, available resources and so on.