Xenobiology
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Xenobiology is often used as a synonym to astrobiology, however, its meaning is now different: while astrobiologists look for life that is based on water and carbon (see carbon chauvinism), xenobiologists look for more "alien" life-forms, not excluding life in non-terrestrial planets, stars or larger or more exotic celestial bodies (Cohen and Stewart 2002).
This concept was widely accepted until the 1980s (For example, the possibility of "abundant biota" in the upper regions of Jupiter's atmosphere was considered in a 1976 paper by Carl Sagan and Edwin E. Salpeter). However, since the 1990s NASA's main goal is astrobiology-like: "look for water" and life based on liquid water. The main reason for this change is that the astrobiologist's lifeform's environment is predictable: we think we know what and where to look for them. The xenobiologist's lifeforms can be so exotic that we don't know what and where to look for therefore this concept is not suitable for space probe and mission planning.
One concept pertaining to xenobiology is that of shadow life. Shadow life refers to life forms that are accessible but that have not been detected by us. An example of shadow life might be a species of microorganisms that do not use RNA or DNA as their genetic code. Such organisms would be difficult to characterize and isolate under current methods due to their different biology.
The xenobiologist concept is now faded away in "hard science" papers, but have not disappeared from the literature.
[edit] References
- Jack Cohen, Ian Stewart: What Does a Martian Look Like? The Science of Extraterrestrial Life. Wiley, 2002
- Sagan, C., and Salpeter, E. E. "Particles, Environments and Possible Ecologies in the Jovian Atmosphere," Astrophysical Journal Supplement, 32, 737 (1976).
- http://spot.colorado.edu/~cleland/articles/Cleland_Copley.pdf
