There are many different planet types in the game, some can be colonized others not. The quality number next to them represents how many hexs (minus 1 for colony capital) you will have access to. So the higher the better.
Mining Planets
There are currently two mining planets in Galactic Civilizations III, Promethion 
, and Thulium 
. These planets are not able to be colonized or conquered, however, they can be mined for those resources which aide in the construction of buildings or ship components. For additional information on mining these resources please see Starbases.
Planetary Traits
Planets may have additional traits that give them specific bonuses. In addition if the Precursor Worlds DLC is installed it will add Precursor planets to the galaxy.
Extreme Planets
There are seven extreme planets either in Galactic Civilizations III or planned to be in the game in the future via patch, DLC (Downloadable Content), or an expansion. Extreme planets by definition require additional technologies or abilities to be able to colonize. The five extreme planets currently in the game are Aquatic 
, Barren 
, Frozen 
, Radioactive 
and, Toxic 
along with two currently not in the game, Heavy 
and Unstable 
.
| Planet Type | Planet Icon | Colonize Immediately | 50% Production Technology | 100% Production Technology | Ability | Mineable |
|---|---|---|---|---|---|---|
| Normal | Yes | None | None | None | No | |
| Aquatic | |
No | Extreme Planet | Colonization Focus | Adaptable | No |
| Barren | |
No | Extreme Planet | Colonization Focus | Adaptable | No |
| Frozen | |
No | Extreme Planet | Colonization Focus | Adaptable | No |
| Radioactive | |
No | Atmospheric Cleansing | Biosphere Perfection | None | No |
| Toxic | |
No | Atmospheric Cleansing | Biosphere Perfection | None | No |
| Heavy | |
No | Unknown | Unknown | None | No |
| Unstable | |
No | Unknown | Unknown | None | No |
| Dead | No | None | None | None | No | |
| Promethion | |
No | None | None | None | Yes |
| Thulium | |
No | None | None | None | Yes |
Remaining Planets
The remaining planet types are your Earth like, Normal planets, which are the main planets races will colonize and conquer and, Dead planets, which are unable to be colonized or mined and are generally useless.