"This afforded an opportunity for a close encounter with Earth as it might appear to an alien spacecraft, and Carl Sagan proposed using this as a "control experiment for the search for extraterrestrial life by modern interplanetary spacecraft." The instruments detected the spectral signature of the chlorophyll from green plants, and signs of an obviously life-altered atmosphere. As Sagan and colleagues wrote in their paper "A search for life on Earth from the Galileo spacecraft" published in Nature, they 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"