section_path: Biological production and role of O/Extraterrestrial free oxygen
section_name: Extraterrestrial free oxygen
paragraph_text: Extraterrestrial free oxygen
  
  In the field of astrobiology and in the search for extraterrestrial life oxygen is a strong biosignature. That said it might not be a definite biosignature, being possibly produced abiotically on celestial bodies with processes and conditions (such as a peculiar hydrosphere) which allow free oxygen, like with Europa's and Ganymede's thin oxygen atmospheres.