Terrestrial planets and moons in may have atmospheres, a layer of gases that surrounds the world and that is held in place by the gravity of the body. Atmospheres shield inhabitants from space radiation and reduce or eliminate the need for pressure and environmental suits and breathing masks. The type of atmosphere a world has depends partially on its orbit. Worlds in Hot orbits often have acidic atmospheres comprised primarily of carbon dioxide and nitrogen. Worlds in Goldilocks and Cold orbits by contrast usually have atmospheres primarily consisting of Nitrogen with various trace gasses.

Atmospheres come in four types. Atmospheres for worlds in Hot or Cold orbits are always type IV. They can never be of type I, II or III due to the temperature extremes. Goldilocks orbit worlds with a Type I atmosphere can freely grow organics. Goldilocks orbit worlds with a type II, III or IV atmosphere may grow organics, but may not have specialisation. Hot and Cold worlds may not normally grow organics, but do benefit from safer pressures and protection from space radiation, thus increasing production.

A world with a type I or II atmosphere MUST have Natural Life. A world in Goldilocks Orbit with an atmosphere can have up to three Climates.

The cost of an atmosphere depends on the size of the world:

World Type	Biomass cost for atmosphere
	Type IV Atmosphere	Type III Atmosphere	Type II Atmosphere	Type I Atmosphere
Small moon	1	2	3	4
Medium moon	3	6	9	12
Large moon, small planet	7	14	21	28
Medium planet	19	38	57	76
Large planet	37	74	111	148

Note: The actual price is calculated per zone; the small moon entry displays the actual price per zone. This is relevant if you have other things that give you extra zones, such as the Underworld special.