Atmospheric Biosignatures

No single gas proves life, so scientists hunt for telling combinations. Beyond oxygen and methane, other candidate biosignatures include phosphine, dimethyl sulfide, and unusual isotope ratios that are hard to produce without biology.

In 2020, a tentative detection of phosphine in Venus's atmosphere set off enormous excitement and controversy. The signal remains disputed, but it showed how atmospheric spectroscopy could one day confirm life on another world.