Let’s say that a "terraformable planet" is a planet who :
- is in the goldilock zone of its star(s)
- has around the same gravity as Earth
- has a solid surface covered with minerals not too toxic for humans
- has enough water for plants and/or algae to grow
- has an atmosphere that can become breathable (even if it takes hundreds of thousands of years following the introduction of Earth plants)
- is mostly safe from meteor impacts
(Criteria chosen for simplicity sake)
The Earth is a blue sky / yellow sun / single moon / 20-ish hours day kind of planet.
But what about terraformable planets ?
What would be the most common sky colors ? Star colors ? Number of moons ? Approximate day lengths ?
Note : I can accept something like “We can deduce a probable answer regarding this one aspect but it’s completely impossible for the other ones”, if it’s justified.
Edit (based on answers) :
The criterias above are completely arbitrary, but please take them into account when answering.
I added them to avoid the vague "Once you have the technology you can terraform anything you want" answer.
More details on this universe (not needed to answer) :
The story I'm working on is not set in the distant future, and in it people do not have the technology to terraform any celestial object they want.
It doesn't really matter how they do it. They can only terraform planets corresponding to these criteria (and a couple other that don't affect answers validity).
My english isn't perfect, please tell me if something isn't clear.