The search for life in the solar system and beyond has to date been governed by a model based on what we know about life on Earth (terran life). Most of NASA's mission planning is focused on locations where liquid water is possible and emphasizes searches for structures that resemble cells in terran organisms. It is possible, however, that life exists that is based on chemical reactions that do not involve carbon compounds, that occurs in solvents other than water, or that involves oxidation-reduction reactions without oxygen gas. To assist NASA incorporate this possibility in its efforts to search for life, the NRC was asked to carry out a study to evaluate whether nonstandard biochemistry might support life in solar system and conceivable extrasolar environments, and to define areas to guide research in this area. This book presents an exploration of a limited set of hypothetical chemistries of life, a review of current knowledge concerning key questions or hypotheses about nonterran life, and suggestions for future research. Table of Contents Front Matter Executive Summary 1 Introduction 2 A Sketch of the Chemistry Behind Known Carbon-based Life on Earth 3 Pushing the Boundaries of Life 4 Alternatives to Terran Biochemistry in Water 5 Origin of Life 6 Why Water? Toward More Exotic Habitats 7 Life Detection and Biomarkers 8 Conclusions and Recommendations Appendix A Glossary Appendix B Biographies of Committee Members and Staff