Planets what are able for colonization

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I could help you with a few suggestions later, perhaps. I'm attempting to make a database containing calculations of all the essential parameters and information for judging if a planet is fit for (long-term) human habitation and/or terraforming for every planet in the game, but I haven't worked on it for a few months after I finished looking at the habitability of all the currently inhabited planets.

EDIT2: Right, I didn't really answer your question; I don't think there are any planets which are uninhabited but currently (relatively) suitable for colonization, unfortunately. Refer to Jinx's post if you haven't read it already, that sums up why there aren't any available planets very well.

If you want to check a few planets yourself, it's relatively easy to judge this from just looking at the infocard of the planet and its location:

1. What surface does (most) of the planet have? Is there anywhere on the planet you'd realistically be able to land a few ships and set up a base? Gas giants are obviously ruled out here, and the same applies to (most) planets covered by liquid, unless you come up with an interesting solution.

2. What is the surface gravity of the planet? For long-term stays or colonization you'd ideally want something between ~0.8 G and ~1.4 G, and for short visits anything under ~2-3 G should work fine, though I wouldn't recommend trying to do any heavy physical work above 1-2 G. You can find the formula for calculating the surface gravity numerous places online; I can't remember it off the top of my head.

3. If you're looking into long term colonization:
a. If you want to terraform it, would the planet be able to retain its (new) oxygen-rich atmosphere? A good rule of thumb here that I'm using is that if the escape velocity of a planet is more than ten times the average speed of a type of gas molecule in its atmosphere, that gas will (probably) remain in the atmosphere, otherwise the molecules will escape into space over time. Planetary atmosphere retention obviously also depends on a heap of other factors, but you don't (usually) have enough information about any given planet in Discovery to look any closer at this, unfortunately. (More information)

If you don't want to bother with any of that; if the planet you're looking at already has an atmosphere and isn't right next to a star or another very massive or intensely radiating object, that's probably a good indication.

b. Is there anything else which would suggest that this planet is suitable/unsuitable for habitation by humans in the infocard? Checking if the planet has a hostile climate, fauna/flora, or atmosphere (e.g. toxic gases) would be a good idea.

tl;dr: Just quickly verifying that it's actually possible to land on the planet surface and that you won't be crushed while doing so would usually indicate that you'd be able to build some kind of habitat on it - for (FL) RP, going much further than that is just over-complicating it in most cases, unless you want to. The first one(s) and 3b (reading through the infocard to check if there's anything interesting on it) are the most important, in my opinion.

- Space

EDIT: Jinx presents a good point as well; terraforming is in most cases a terribly complicated, expensive and lengthy process. The above wall of text is more directed towards what would be needed for a small base/installation on the surface with its own air supply (except point 3a), not long-term colonization and terraforming, which realistically only the houses would be able to do.

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