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Celestial body

Terraforming is the act of changing the planet classification of a planet in order to make it more habitable for the empire's species. The base technologies requires significant society research to unlock and each terraforming project requires significant investments of Energy and time.

The first time a planet is terraformed, there's a chance of triggering a terraforming event. Terraformed planets can't get colony events.

Terraforming is started via a button in Planet Detail view. The world must be surveyed and within your borders. Only habitable worlds and barren worlds that have the rare Terraforming Candidate modifier can be terraformed. The expansion planner screen can be used to find these rare candidates.

It is possible to terraform inhabited planets if the empires has the Ecological Adaptation technology. Doing so inflicts a 20% Happiness penalty on the planet for the duration of the procedure.

Ecumenopolis worlds are created via decisions rather than terraforming. They must be inhabited but pops do not suffer a happiness penalty during the process.

The following planet modifiers are always removed when terraforming a planet:

If the planet is being terraformed into either a Machine or Hive World the following modifiers are also removed:

If the planet is terraformed into a Machine World, the Paradise Made modifier is also removed. Additionally, if there are any Pops on the planet without the Cybernetic, Mechanical, or Machine traits, they're all killed and an Organic Slurry deposit is added.

When and if terraforming a planet to Hive or Machine World, keep in mind that all planetary features, excluding a few rare ones that give access to rare resources, will always be removed.

Terraforming cost and speed can be affected by the following:

Game concepts

See the article here:

Terraforming - Stellaris Wiki