Vacuum
Source GM Core pg. 96
Space is a vacuum, meaning it contains no breathable air and has zero gravity. Creatures in a vacuum are at risk of suffocation and take minor bludgeoning damage each minute. In addition, they are untethered and require special propulsion to move. Space has no effective temperature, and a creature retains its body heat for several hours in a vacuum. Sound doesn't travel in a vacuum, meaning most sonic effects don't function. Creatures with the cosmic trait are immune to many of the effects of a vacuum.
Decompression
Source GM Core pg. 97
Decompression occurs when a creature suddenly transitions from a pressurized environment to a vacuum, such as by getting shoved out of an airlock or being inside a starship that sustains heavy damage. Such a creature takes moderate bludgeoning damage and immediately begins suffocating (they can't hold their breath). Decompression can also apply to characters in underwater environments.