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: http://www.astrosociety.org/edu/publications/tnl/58/planetprotect2.html
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Where and how are we looking for evidence of life?
Astrobiology is a multidisciplinary scientific research program that studies the origin, evolution, distribution and fate of life in the universe. (See "The Universe in the Classroom," No. 51, Astrobiology: The Final Frontier of Science Education, by Jodi Asbell-Clarke and Jeff Lockwood.
Scientifically, its cutting edge research is a synthesis of disciplines — from astronomy to zoology, from ecology to molecular biology, from geology to genomics — all focused on the common goal of discovering the thread of life in the universe. By using a variety of advanced technologies — both on Earth and in space — astrobiologists seek to discover the intricate chain of cause-and-effect that determines how life originates and evolves, and the resultant implications for the destiny of the worlds.
Because the universe is an immense place, it makes sense to search for evidence of life in more than one way. In addition to focusing on what we know about life on Earth, especially in extreme environments, astrobiology currently comprises three basic types of searches in space, each employing different technologies, looking in different places, and expecting to find different kinds of data:
1) The Search for Extraterrestrial Intelligence (SETI): the search within our galaxy using radiotelescopes to listen for electromagnetic signals from intelligent extraterrestrial civilizations,
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| Aerial view of the Very Large Array, looking north-northeast. This set of large radio telescopes is used for a variety of astronomical observations including SETI searches. Here the antennas are in their closest configuration (D configuration). Photo by Dave Finley: Courtesy NRAO/AUI |
2) The Search for Extrasolar Planets and Terrestrial-like Planets: This effort actually encompasses two types of searches: the first, using Doppler detection methods to look for evidence of stars that have nearby planets and solar systems of their own; and the second using a technique called 'interferometry' to translate optical data from far off terrestrial-sized planets into chemical 'fingerprints' to look for places that may have atmospheres indicative of habitability or even life's presence.
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| This is one of the designs for the proposed Terrestrial Planet Finder mission. Like the VLA, images from a collection of smaller telescopes are combined to give the same results that could be obtained from a much larger telescope. |
3) Exobiology and Solar System Exploration: - the search within the solar system to detect evidence for the origin, evolution and existence of non-intelligent life, which would probably be microbial, although not necessarily simple (for example, anthrax and parasites may be small, but they reflect a long evolutionary history and are biologically quite complex).
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| The Viking 2 Lander was active on Mars in 1976. It had an arm that reached out to scoop up some soil and conducted three different experiments to determine if there was life on Mars. This pair of pictures shows the arm successfully pushing away a rock to take a soil sample. The results were disappointing so some. For a discussion of the results, go to: http://www.msss.com/http/ps/life/life.html |
The search types — SETI vs. Extrasolar Planets vs. Exobiology — differ in many important ways. The search for extrasolar planets and terrestrial-like planets is really a search for locations or environments in the vastness of space. Is there land out there Columbus? Finding and mapping places helps us know more about what's out there, but without necessarily indicating anything about life, at least initially. This is in contrast with the other two search types. Positive findings in either SETI or exobiological searches would be interpreted as more indicative of some type of life or beings, either past or present. However, here again, the searches are distinctly different, especially from a planetary protection perspective.
In addition to searching vastly different locations and distances from Earth (within our galaxy vs. in the solar system), SETI and exobiological searchers each presumes distinctly different types of extraterrestrial life (intelligent and complex vs. microbial and biologically simpler). In addition, both searches employ different equipment and methods (radio telescopes vs. spacecraft and scientific instruments), and involve distinctly different data (incoming electromagnetic signals vs. biological, chemical and/or geological evidence). Searches for extraterrestrial intelligence (ETI) use non-intrusive, indirect methods, with no environmental impacts or potential planetary cross contamination concerns, either on Earth or in space. A positive finding would presumably be in the form of a signal or message. In contrast, the exobiological searches for life employ spacecraft, scientific equipment and experiments within the solar system, and raise questions about environmental impacts and planetary cross contamination both on Earth and the celestial bodies visited.
Taken together, all these differences have significant implications for activities during the period of exploration as well as for future actions if and when extraterrestrial life is discovered. The discovery of any type of extraterrestrial life, based on direct or indirect evidence, would have significant scientific, societal, practical and ethical implications.