Galileo's Earth Fly-By Discoveries

In 1990, NASA directed the Galileo spacecraft towards Earth to search for signs of life. It did detect signs strongly suggestive of life on Earth. These included abundant gaseous oxygen, a widespread surface pigment with a sharp absorption edge (chlorophyll in vegetation), and atmospheric methane in extreme thermodynamic disequilibrium. Moreover, the spacecraft identified narrow-band, pulsed, amplitude-modulated radio transmissions-a unique marker of intelligence. These observations served as a vital control experiment for the search for extraterrestrial life by modern interplanetary spacecraft.