One of the possible atmospheres in SEIII, SE4 nad SEV. Selecting this type as breatheable during race creation allows you to have maximum facilities on tiny airless moons at the start of the game. It is a useful selection in SEIII as well, since it allows you to colonise asteroids staight away.
Note that in SE4 and SE5 it is impossible to have a gas giant with atmosphere: none, even using atmospheric modification plants. This helps balance the early-game advantage of plentiful moons with a late-game lack of breathable gas giants.