LYCOS RETRIEVER 
Extraterrestrial Life: Planets
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The quest for extraterrestrial life doesn't happen only in science fiction. This book describes the startling discoveries being made in the very real science of astrobiology, an intriguing new field that blends astronomy, biology, and geology to explore the possibility of life on other planets. Jeffrey Bennett takes readers beyond UFOs to discuss some of the tantalizing questions astrobiologists grapple with every day: What is life and how does it begin? What makes a planet or moon habitable? Is there life on Mars or elsewhere in the solar system? How can life be recognized on distant worlds?
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There are several hypotheses regarding the origin of extraterrestrial life. One proposes that its emergence occurred independently, in different places in the universe. An alternative hypothesis is panspermia, which holds that life emerging in one location then spreads between habitable planets. These two hypotheses are not mutually exclusive. The study and theorization of extraterrestrial life is known as astrobiology, exobiology or xenobiology. Speculative forms of extraterrestrial life range from sapient beings to life at the scale of bacteria.
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Sir - The fields of extraterrestrial life, extrasolar planets, origin of life, theoretical biology, interstellar travel and communication, extraterrestrial intelligence and civilization, and SETI have no generally accepted collective nomenclature. Suggestions include astrobotany, astrobiology, bioastronomy, astropalaeontology and astroarchaeology, cosmobiology (unfortunately linked to astrology), and biocosmology, bioastronautics, space biology, planetary biology, intellexobiology, and exosociology, each of which fails as a general term in taking as axiomatic that intelligence, technology and civilization require life or society, an arguable and imprudent assumption. The acronym SETI (Search for Extraterrestrial Intelligence) excludes biology and is inelegant.
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Most scientists believe that if extraterrestrial life exists, its evolution would have happened in different places in the universe. Others believe that life started on a small number of planets and spread to other planets.
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