Outgassing (sometimes called offgassing) is the release of gas that was dissolved, trapped, frozen, or absorbed in material. Outgassing can include sublimation and evaporation (phase transitions of a substance into a gas), desorption, seepage from cracks or internal volumes, and gaseous products of slow chemical reactions. All can potentially introduce contaminants into a previously clean product. The levels achieved by Gecko meet both NASA and ESA (European Space Agency) required specifications.