“Sagan desperately wants to find life someplace, anyplace—on Mars, on Titan, in the solar system or outside it,” one of his Viking colleagues said recently. “In all the divergent things he does, that is the unifying thread. I don’t know why, but if you read his papers or listen to his speeches, even though they are on a wide variety of seemingly unrelated topics, there is always the question ‘Is this or that phenomenon related to life?’ People say, ‘What a varied career he has had,’ but everything he has done has had this one underlying purpose.”

Sagan was asked the other day why he thought it was that he, and others, are so interested in trying to find life beyond the earth. “I think it’s because human beings love to be alive, and we have an emotional resonance with something else alive, rather than with a molybdenum atom,” he said. “Why are people interested in other animals? Why are we interested in the life history of the armadillo? Why do we go to Antarctica to find out what the emperor penguins have been doing lately? It’s fun, because we are primarily drawn to things that are alive.”

From a June 28, 1976 profile in The New Yorker by Henry S. F. Cooper titled “A Resonance With Something Alive”