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C.F. Chyba (SETI Institute and Department of Geological and Environmental Sciences, Stan)
The word exobiology was coined at the dawn of the space age. But the subsequent discovery of high venusian surface temperatures, the demonstration that martian seasonal albedo changes were due to windblown dust rather than vegetation, the utter sterility of the Moon, and the absence of organics on Mars, made exobiology appear less and less relevant within our Solar System. This has changed profoundly in the light of rapidly growing knowledge about the origin and distribution of terrestrial life and further discoveries in planetary exploration. While substantial mysteries remain in the former, research in the RNA World hypothesis demonstrates the possibility of alternatives to Earths contemporary DNA-Protein biology. Biological prospecting on Earth strongly suggests the feasibility of deep subsurface ecologies entirely independent of the Sun, and DNA sequencing suggests that the origin of life itself may have occurred in hot or possibly deep environments. At the same time, the discovery of lunar and martian meteorites suggests that the worlds of at least the inner Solar System may never have been biologically isolated. There is also growing evidence for a subsurface ocean on Europa. The range of potentially habitable worlds appears broader than ever, even as it has become clear that extrasolar planets are common. Simultaneously, the connections between astronomy and the terrestrial origin of life have grown increasingly vital. Important areas for further research include the relationship of organic chemistry in the ISM to that found in meteorites, as well as the use of meteorites as an empirical probe for claims of the origins of life at depth. Understanding cometary organic chemistry, and improving our knowledge of the lunar bombardment history, provide two further examples, among many others. Altogether, the prospects for extraterrestrial life in our Solar System seem brighter now than they have seemed since Viking. The Mars meteorite controversy reiterates the lesson of those missions that geological and chemical context is critical for evaluating the possibility of biology. Planetary exploration must once again grapple with the challenge of biological remote detection, and forward contamination issues, especially with respect to entering and operating in liquid water environments, must be rigorously examined.
The author(s) of this abstract have provided an email address for comments about the abstract: chyba@seti.org