Scientific Perspective: The Search for Life in the Universe
Christopher P. McKay (JPL)
The search for a second genesis of life in the universe address deep philosophical and scientific questions: Is life common in universe? Are there alternative biochemistries for life? Several observations motivate the search. These include the presence of organic material in the outer solar system, in meteorites, and the interstellar medium; the evidence for Earth-like planets around other starts; the early occurrence of life on Earth; the presence of past and present liquid water environments in other worlds of our solar system. The search for a second genesis of life includes work in laboratories aimed at creating life, missions to other worlds in our solar system, the search for signs of life on extrasolar planets, and of course SETI. Probably, the best strategy for a second genesis of life in the worlds of our solar system is the detection and detailed characterization of organic material. This make use of the fact that life selects certain organic molecules, abiotic chemistry does not. On extrasolar planets the detection of atmospheric oxygen is the most promising approach. High levels of oxygen on an Earth-like planet orbiting a Sun-like star would be convincing evidence for life and suggestive evidence for complex life. Neither the vast number of stars and planets, nor the principle of mediocrity give us any guidance on the likelihood of life beyond the Earth. The question for a second genesis of life in the universe is an empirical one and all methods of search should be engaged.