Carl Edward Sagan (November 9, 1934 - December 20, 1996) was an American astronomer and astrobiologist and a highly successful popularizer of astronomy, astrophysics, and other natural sciences. He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI). He is world-famous for writing popular science books and for co-writing and presenting the award-winning 1980 television series “Cosmos: A Personal Voyage”, which has been seen by more than 600 million people in over 60 countries, making it the most widely watched PBS program in history. A book to accompany the program was also published. He also wrote the novel “Contact”, the basis for the 1997 Robert Zemeckis film of the same name starring Jodie Foster. During his lifetime, Sagan published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he frequently advocated skeptical inquiry, humanism, and the scientific method.
Sagan was central to the discovery of the high surface temperatures of the planet Venus. He was among the first to hypothesize that Saturn’s moon Titan and Jupiter’s moon Europa may possess oceans (a subsurface ocean, in the case of Europa) or lakes, thus making the hypothesized water ocean on Europa potentially habitable for life. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot, life-hostile planet through greenhouse gases. Sagan is best known, however, for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.
Source: Wikipedia http://en.wikipedia.org/wiki/Carl_Sagan