Thermophiles, early biosphere evolution, and the origin of life on Earth: Implications for the exobiological exploration of Mars

摘要

Mars holds great interest for exobiology and presently stands center stage in our plans to explore the inner solar system for signs of past or present life. With the spectacular success of the Pathfinder mission [Golombek, 1997] and upcoming mapping efforts by the Mars Global Surveyor orbiter [Albee et al, 1998], it is an especially appropriate time to revisit some important issues in Mars exobiology. The papers making up this Journal of Geophysical Research‐Planets special issue on Mars were the outgrowth of an American Geophysical Union special session entitled “Exploring for a Martian Biosphere,” which was presented at the fall meeting in San Francisco in 1995 [Farmer, 1995a]. Together these papers provide a context for evaluating some fundamental issues in the exobiological exploration of Mars. Topics covered fall into the following broad categories: (1) environments and conditions required for the origin of life (hydrothermal environments as sites for prebiotic chemical synthesis [Shock and Schulte, this issue]), (2) early Martian environments as a context for the evolution and diversification of life on Mars (early impact hazards [Sleep and Zahnle, this issue], early volatile and climate history of Mars [Haberle, this issue], and ice‐covered lakes as habitats for early life [Doran et al., this issue]), (3) exploring for extant Martian life (results of the Viking missions [Klein, this issue], environmental extremes for Martian life [Clark, this issue], and planetary protection and Mars sample return [DeVincenzi et al., this issue]), and (4) exploration strategies (phosphate minerals as targets for chemofossils [Mojzsis and Arrhenius, this issue] and the role of robotic surface missions [Stoker, this issue]).