Don't dismiss astrobiology.

Jeffrey L. Bada (“A field with a life of its own,” Books et al. , 7 Jan., p. [46][1]) repeats the criticism of astrobiology that the biologist George Gaylord Simpson leveled at exobiology in the pages of Science in 1964: “this ‘science’ has yet to demonstrate that its subject matter exists!” ([1][2]). In fact, astrobiology is far more than the study of extant extraterrestrial life, but even if that were the sole object of the field, Simpson's criticism must still seem bizarre to many scientists. Much of the most important and compelling research in astronomy, physics, and other fields is exactly concerned with the study of or search for objects or phenomena that may not exist—and that could (and sometimes do) turn out not to exist. Black holes were hypothesized and then searched for long before compelling evidence regarding their existence accumulated. The same can be said of the search for high-temperature superconductors, proton decay, or the current holy grail of unification, the Higgs boson. Why should we suddenly become giggly when it is biology at stake, rather than physics? In fact, astrobiology merely confronts what is familiar, even commonplace, in many of its sister sciences. There is nothing unique about that, and there is no reason for it to make us uneasy or afraid. 1. 1.[↵][3] 1. G. G. Simpson , Science 143, 769 (1964). [OpenUrl][4][FREE Full Text][5] # {#article-title-2} In his review of the book The Living Universe (“A field with a life of its own,” Books et al. , 7 Jan., p. [46][1]), J. L. Bada presents a mistakenly narrow view of astrobiology. Its aim is not just to find life but, rather, to both determine and understand the distribution of life in the universe through time. One extreme possibility is that life exists only on Earth, has never existed anywhere else, and will never be present beyond Earth's orbit. At the alternative extreme, life may have originated on multiple bodies in our solar system and may be ubiquitous beyond. No matter what the answer proves to be, astrobiologists will want to know how the actual distribution of life relates to the occurrence of different planetary environments. Hence, in addition to exploring for evidence of life beyond Earth, astrobiologists study the extreme limits to life, the conditions that make environments habitable, the origin and evolution of life on Earth, the processes responsible for the occurrence of habitable environments in our solar system, and the occurrence of planets and their habitability beyond our solar system. # Response {#article-title-3} The letters by Jakosky et al. and chyba demonstrate that my paraphrasing of Simpson's statement about astrobiology (his exobiology) being a field without a known subject elicits the same defensive response it did over 40 years ago ([1][6]). I certainly agree that the search for life beyond Earth is an important and engaging human endeavor. Simpson's original argument against exobiology as a distinct discipline is that we could learn a lot more about life by studying it right here on Earth, rather than attempting to find life somewhere else. Today, we still do not fully understand how life began on our planet, although there is optimism that this will change in the near future ([2][7]). It is reasonable to assume that if the conditions that gave rise to life on Earth are widespread, then life must have begun and probably still exists elsewhere. And, of course, we will never know unless we search using the best available tools at our disposal. The fact that we do not yet have any known example of extraterrestrial life makes this challenge all the more exciting but at the same time all the more difficult, especially during this present period of shrinking science budgets. 1. 1.[↵][8] 1. W. Vishniac , Science 144, 245 (1964). [OpenUrl][9][PubMed][10][Web of Science][11] 2. 2.[↵][12] 1. J. L. Bada , Earth Planet. Sci. Lett. 226, 1 (2004). 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