Astrobiology in the next forty years  updated Aug. 3, 2005  D. Carrigan carrigan@fnal.gov (subject line must be sensible)

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The  NASA Astrobiology Institute and many other institutions are actively studying astrobiology. There are a number of potential signatures for  life and intelligence beyond the earth:
   
Planets and satellites (Mars, Europa) - Rovers, surveyors, and orbiters have produced some evidence of methane on Mars but there is strong controversy over whether this is necessarily biologically produced. There is also a controversial signature from the 1976 Viking lander program that some argue may indicate biological activity. 
     Meteors: Some meterors collected in Antartica can be traced to Mars. One, ALH84001, has given very controversial evidence of Martian fossils.
    Atmospheres of extrasolar planets: A recent Hubble observation of extrasolar planet HD 209458b  has seen evidence of oxygen and carbon in the planet's atmosphere.
    Planetary and galactic habitable zones: Better understanding of potential habitable zones is extremely important for astrobiology.
    Finally the Search for Extraterrestrial Intelligence might find evidence that would suggest the existence of life or intelligence.
How rare is life in the univese? This subject has been covered recently in the book Rare Earth  by Ward and Brownlee. Rare Earth is useful but I take issue with the word “rare” and find their conclusions sometimes pushed aside by new developments (more planets than expected, extremophiles, symbiosis). A book “Not So Rare Earth” might be just as interesting and closer to the facts.  SETI: Messages from space are a staple of science fiction (see below). A SETI signal would be strong evidence for extraterrestrial intelligence. One difficulty may be that searches have a “drunk searching for his keys under the light post" problem. More information on SETI appears elsewhere on this site. Serious searches are now underway at the SETI Institute and other institutions.

The Fermi question or paradox: In the early fifties Fermi may have observed that it is not so hard to get around the galaxy on the time scale of evolution on the earth. If that is so we might expect spacemen to be everywhere but there has never been a confirmed contact. This suggests space faring life may be rare. The New Yorker cartoon from 1950 has been used to try to tie down when Fermi made this observation. 

rare earth
The Siren Stars
New Yorker