Confidence of Life Detection: The Problem of Unconceived Alternatives.

Potential biosignatures that offer the promise of extraterrestrial life (past or present) are to be expected in the coming years and decades, whether from within our own solar system, from an exoplanet atmosphere, or otherwise. With each such potential biosignature, the degree of our uncertainty will be the first question asked. Have we really identified extraterrestrial life? How sure are we? This paper considers the problem of unconceived alternative explanations. We stress that articulating our uncertainty requires an assessment of the extent to which we have explored the relevant possibility space. It is argued that, for most conceivable potential biosignatures, we currently have not explored the relevant possibility space very thoroughly at all. Not only does this severely limit the circumstances in which we could reasonably be confident in our detection of extraterrestrial life, it also poses a significant challenge to any attempt to quantify our degree of uncertainty. The discussion leads us to the following recommendation: when it comes specifically to an extraterrestrial life-detection claim, the astrobiology community should follow the uncertainty assessment approach adopted by the Intergovernmental Panel on Climate Change (IPCC).

Astrobiology and society: building an interdisciplinary research community.

This paper reports recent efforts to gather experts from the humanities and social sciences along with astrobiologists to consider the cultural, societal, and psychological implications of astrobiology research and exploration. We began by convening a workshop to draft a research roadmap on astrobiology's societal implications and later formed a Focus Group on Astrobiology and Society under the auspices of the NASA Astrobiology Institute (NAI). Just as the Astrobiology Science Roadmap and various astrobiology science focus groups have helped researchers orient and understand their work across disciplinary contexts, our intent was to apply the same approach to examine areas beyond the physical and life sciences and expand interdisciplinary interaction and scholarly understanding. These efforts continue as an experiment in progress, with an open invitation to interested researchers-astrobiologists as well as scholars in the humanities and social sciences-to become involved in research, analysis, and proactive discussions concerning the potential impacts of astrobiology on society as well as the possible impacts of society on progress in astrobiology.

Critical issues in the history, philosophy, and sociology of astrobiology.

Fifty years after serious scientific research began in the field of exobiology, and forty years after serious historical research began on the subject of extraterrestrial life, this paper identifies and examines some of the most important issues in the history, philosophy, and sociology of what is today known as astrobiology. As in the philosophy of science in general, and in the philosophies of particular sciences, critical issues in the philosophy and sociology of astrobiology are both stimulated and illuminated by history. Among those issues are (1) epistemological issues such as the status of astrobiology as a science, the problematic nature of evidence and inference, and the limits of science; (2) metaphysical/scientific issues, including the question of defining the fundamental concepts of life, mind, intelligence, and culture in a universal context; the role of contingency and necessity in the origin of these fundamental phenomena; and whether or not the universe is in some sense fine-tuned for life and perhaps biocentric; (3) societal issues such as the theological, ethical, and worldview impacts of the discovery of microbial or intelligent life; and the question of whether the search for extraterrestrial life should be pursued at all, and with what precautions; and (4) issues related to the sociology of scientific knowledge, including the diverse attitudes and assumptions of different scientific communities and different cultures to the problem of life beyond Earth, the public "will to believe," and the formation of the discipline of astrobiology. All these overlapping issues are framed by the concept of cosmic evolution-the 13.7 billion year Master Narrative of the Universe-which may result in a physical, biological, or postbiological universe and determine the long-term destiny of humanity.

NASA and the search for life in the universe.

Almost from its beginnings in 1958, the National Aeronautics and Space Administration (NASA) set up a life-science program. Because one of the priorities of the organization is to search for life beyond Earth, NASA began designing spacecraft to unravel the mysteries of Mars. The effort to search for life on Mars culminated in the landing of two Viking spacecraft on the surface of the planet in 1976. Although the biology experiments conducted as part of these missions provided some evidence for the possibility of life, the scientific consensus was that they drew a blank. In 1996, however, the 'Mars rock' rekindled interest in life in our solar system. The discovery of an ocean on the Jovian moon Europa, of organic molecules on the Saturnian moon Titan and persuasive evidence that water once flowed on Mars suggests that the solar system is still of considerable exobiological interest. In addition, since 1995 approximately 175 planets have been found beyond our solar system. Although these discoveries are gas giants, NASA spacecraft might soon detect Earth-sized planets. The search for life in the universe continues.