Astrobiology is the study of life throughout the universe, also known as exobiology or bioastronomy. It remains, as the evolutionary biologist George Gaylord Simpson put it, "a science looking for a subject." Astrobiologists face the problem of having access to biological samples from only one planet. This makes it difficult to know if life elsewhere, assuming it exists, follows the same or a similar pattern. Speculation cannot be confined to DNA-based organisms, and there is even the possibility that we may have difficulty in recognizing certain alien species as living entities. The term "astrobiology" was used as early as 1941 as the title of a paper by L. J. Lafleur1 (a pdf is available of this through the NASA ADS abstract service) and was also used by Gavriil Tikov in 1953 as the title of a book. See also extraterrestrial life, variety.
1. Lafleur, L. J. "Astrobiology," Astronomical Society of the Pacific Leaflets, 3, 333, 1941.