A search for life on Earth from the Galileo spacecraft.
In its December 1990 fly-by of Earth, the Galileo spacecraft found evidence of abundant gaseous oxygen, a widely distributed surface pigment with a sharp absorption edge in the red part of the visible spectrum, and atmospheric methane in extreme thermodynamic disequilibrium; together, these are strongly suggestive of life on Earth.  Moreover, the presence of narrow-band, pulsed, amplitude-modulated radio transmission seems uniquely attributable to intelligence.  These observations constitute a control experiment for the serach for extraterrestrial life by modern interplanetary spacecraft.
Sagan
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Laboratory for Planetary Studies, Cornell University, Ithaca, New York 14853, USA.
Thompson
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Carlson
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Gurnett
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Hord
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D001272:Atmosphere; D018534:Earth, Planet; D018559:Exobiology; D005118:Extraterrestrial Environment; D008697:Methane / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011846:Radio Waves; D013026:Space Flight; D018531:Spacecraft; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D014867:Water
D014867:Water; D008697:Methane; D010100:Oxygen