Carl Sagan—A Tribute

Carl Sagan—A Tribute
Carl Sagan—A Tribute Carl Sagan's scientific life centered on the search for life in the universe. The two images on our cover symbolize the range of his work: the amino acid glycene, seen here in crystallized form, is one of the crucial building blocks of life on Earth. Its spectra have been detected in gas and dust clouds among the stars, suggesting that it—and the life that can spring from it—may be common in the universe. The nearby planet Mars has carved into its surface evidence that it once possessed a climate that may have supported life. Here Ma'adim Vallis, a 600-kilometer-long channel (400 miles), drains into the crater Gusev. Channels like this, with a morphology typical of earthly rivers, show that water once flowed on Mars. Discoveries like these, of the elements of life, propelled Carl's work Glycene photograph: Alfred Pasieka, Peter Arnold, Inc. Mars image: U.S. Geological Survey, Flagstaff

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