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6 SETI and Astrobiology NASA AND SETI The search for intelligent life on worlds beyond Earth represents the most romantic and publicly accessible aspect of the search for life, yet is perhaps the most problematic. No as yet known remote-sensing technique can detect the presence of intelligent versus complex life forms, other than by listening for electromagnetic forms of communication leaking from or deliberately sent from another world.) Human civilization has put chlorofluoro- carbons in the stratosphere, which are demonstrably the product of a technological civilization but require high spectral resolution to detect. Further, the damaging effects on the stratospheric ozone layer of these compounds imply that a civilization would do this only for a minuscule amount of time, several decades, making detection of such compounds very unlikely. Early attempts in the 1950s and 1960s to detect radio signals from another civilization yielded no positive results. Proponents of the search understood the need to build tunable receivers that could scan enormous numbers of very narrow frequency bands at high speed, but the ability to do so was technologically limited until the 1980s, when inexpensive computing capability and receiver technologies matured. In the early 1990s, NASA involved itself in the search through a project known as the High-Resolution Microwave Survey (FIRMS), which planned to utilize two complementary search modes: an all-sky survey element (the responsibility of the Jet Propulsion Laboratory) and a targeted search element (the responsibility of the Ames Research Center). Both elements involved state-of-the-art digital spectrum analyzers and signal-processing equipment to carry out the observations and data-processing activities automatically, and the use of large radio telescopes such as those in NASA's Deep Space Network, the National Astronomy and Ionosphere Center's Arecibo Observatory in Puerto Rico, and others. THE SETI INSTITUTE In 1993, Congress terminated support for the HRMS project after a floor debate on the question of extraterres- trial life. Scientists from the Ames Research Center's targeted-search team then regrouped through a Silicon Valley-based not-for-profit organization, the SETI (Search for Extraterrestrial Intelligence) Institute, which had been founded some 8 years before.2 Scientists and engineers from the SETI Institute formed the core of the targeted-search team. 44

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SETI AND ASTROBIOLOGY 45 As a non-profit organization, the SETI Institute was in a unique position to acquire the targeted-search equipment, representing about $58 million of taxpayer investment, and to use it for the search for extraterrestrial intelligence. Private fund-raising efforts increased the SETI Institute' s expenditures from $2 million per year early in its existence to about $6 million per year at the time the HRMS project was canceled. To implement NASA's targeted search, the SETI Institute first secured an agreement with NASA for a long-term loan of the partially built Targeted Search System. Then it raised private funds to complete the expansion of the system and to conduct the planned observations, which have been under way since 1995 under the name "Project Phoenix." Project Phoenix does not scan the whole sky. Rather, it scrutinizes the vicinities of about a thousand nearby stars (i.e., within 200 light-years) with properties like those of the Sun. Phoenix looks for signals between 1 and 3 GHz. Exceedingly narrow band signals are assumed to be the "signature" of an intelligent transmission. The spectrum searched by Phoenix is broken into very narrow, 1-Hz-wide channels, so 2 billion channels are examined for each target star. An automatic detection algorithm, one of the major software inventions of the SETI Institute, enables long-term observation with only occasional human intervention. Observations are currently being made during two 3-week sessions each year using the 1,000-foot radio telescope at Arecibo. With about half of the target-list stars searched, no positive results have been found. However, the volume of the Milky Way searched by Project Phoenix is vanishingly small, especially when compared with, for example, what microlensing surveys will cover in the search for planets of the mass of Earth. A new project, the Allen Telescope Array, will cover a much larger volume of space and a much larger frequency domain. It is a telescope system designed and built specifically for the search for extraterrestrial intelligence, to be sited at a University of California observing station in northern California, with private dona- tions totaling more than $12 million. Interestingly, the Allen Telescope Array is pioneering a variety of concepts to be employed in the proposed Square Kilometer Array, a project highly rated in the most recent astronomy decadal survey.3 ASSESSMENT OF THE SETI INSTITUTE On its face, the SETI Institute appears to be a model for science that is driven entirely by private donations with a particular result in mind. In fact, however, the SETI Institute does receive federal research grants for a variety of projects in the general area of astrobiology. It does so because the institute serves as an organizational structure for a number of scientists who work at the Ames Research Center but do not have civil service positions. Approximately 35 investigators hold NASA grants or cooperative agreements through the SETI Institute that fund individual principal investigator-based research programs. Thus, the SETI Institute is in fact two different entities: a soft-money institution for research over a range of areas of astrobiology, largely funded with federal money, and a donor-financed effort to develop technologies to search for intelligent life throughout a significant fraction of the Milky Way. The SETI Institute has done an excellent job in developing programs in both arenas, which synergistically provide scientific breadth, vigor, and the resources for conducting a search that the federal government opted out of a decade ago. The SETI Institute' s leadership consists of scientists of the highest reputation Frank Drake, Jill Tarter, and Christopher Chyba who have personally invested their careers in the science of astrobiology. Stu- dents working at the SETI Institute from the Bay Area and elsewhere contribute their own intellectual energy and have produced high-quality research projects that in some cases lead to Ph.D. dissertations. Overall, the scientific quality of the programs and their output are high. COEL doubts that the SETI Institute is a model that could be replicated elsewhere. It has always had strong involvement from a few select Silicon Valley pioneers who have themselves contributed substantial intellectual and capital resources, thereby providing the momentum for the institute to pursue its long-range goals. But the committee sees the SETI Institute as an important national resource in astrobiology, primarily through its ability to privately fund a high-risk venture with a potentially historic payoff. Further, COEL sees no merit in debating the validity of a search whose negative results arguably tell us little about the ubiquity of life. The debate has no merit because the foundational motivation for the search is the popular aspiration to communicate with other forms of intelligence as much like or unlike us as we care to imagine. It

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46 LIFE IN THE UNIVERSE would be dissembling, to say the least, to discourage such a search (especially one enabled by private funding) at the same time that astrobiology as a whole taps in to the same emotions and aspirations to excite the public about the general search for life's ongins, evolution, and cosmic ubiquity. The leadership of the SETI Institute has forged a unique endeavor out of private and public funds, maintained a high standard of scientific research through its peer-reviewed research activities, and articulated clearly and authoritatively the rationale for approaches to a comprehensive search for extraterrestrial intelligence. NOTES AND REFERENCES 1. J. Tarter, "The Search for Extraterrestrial Intelligence (SETI)," Annual Review of Astronomy and Astrophysics 39: 511-548, 2001. 2. For more details about the SETI Institute, see its Web site . 3. Board on Physics and Astronomy/Space Studies Board, National Research Council, Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C., 2001.