A life of research
Born in New York, he trained at the University of Chicago and later worked at Cornell. His research investigated planetary environments and chemical processes that might precede the emergence of life.
He contributed scientific ideas to several space missions. Data returned by spacecraft made it possible to test models of Venus, Mars and more distant worlds against direct new observations.
Understanding the contribution
His work helped explain the extreme heat of Venus through a powerful greenhouse effect. Comparative studies of atmospheres show how planets of similar size can follow radically different evolutionary paths.
Sagan also explored the search for extraterrestrial life and the possibility of interstellar communication. He distinguished a compelling hypothesis from a confirmed result: exciting questions still require careful standards of evidence.