99 Could we detect extraterrestrial life?
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This article is from the Astronomy FAQ, by Joseph Lazio (jlazio@patriot.net) with numerous contributions by others.
99 Could we detect extraterrestrial life?
By Steve Willner <swillner@cfa.harvard.edu>
Yes, although present observations can do so only under optimistic
assumptions. Radio and optical searches currently underway are aimed
at detecting "beacons" built by putative advanced civilizations and
intended to attract attention. More sensitive searches (e.g., Project
Cyclops) that might detect normal activities of an advanced
civilization (similar for example to our military radars or TV
stations) have been proposed but so far not funded. No funding of
these is likely until the search for beacons is far closer to being
complete. Why get involved with the difficult until you are done with
the easy?
Ordinary astronomical observations are most unlikely to detect life.
The kinds of life we speculate about would be near stars, and the
light from the star would conceal most signs of life unless a special
effort is made to look for them.
Within the solar system, the Viking landers found conditions on the
surface of Mars unlikely to support life as we know it. The mass
spectrometer found too little carbon, which is the basis for organic
molecules. The chemistry is apparently highly oxidizing as well.
Some optimists have nevertheless argued that there still might be
life on Mars, either below the surface or in surface regions not
sampled by the landers, but most scientists consider life on Mars
quite unlikely. Evidence of surface water suggests, however, that
Mars had a wetter and possibly warmer climate in the past, and life
might have existed then. If so, there might still be remnants
(either living or fossil) today, but close examination will be
necessary to find out.
Other sites that conceivably could have life include the atmosphere
of Jupiter (and perhaps Saturn) and the presumed liquid water under
the surface ice of Jupiter's satellite Europa. Organisms living in
either place would have to be very different from anything we know on
Earth, and it's hard to know how one would even start to look for
them.
Concepts for specialized space missions that could detect Earth-like
planets and return spectral information on their atmospheres have been
suggested, and either NASA or ESA may launch such a mission some time
in the next two decades (see
<URL:http://techinfo.jpl.nasa.gov/www/ExNPS/HomePage.html> and
<URL:http://ast.star.rl.ac.uk/darwin/>). The evidence for life would
be detection of ozone (implying oxygen) in the planet's atmosphere.
While this would be strong evidence for life---oxygen in Earth's
atmosphere is thought to have come from life---it would not be
ironclad proof, as there may be some way an oxygen atmosphere could
form without life.
For more information, see references at the end of F.06. Also, check
out the SETI Institute Web site at <URL:http://www.seti-inst.edu>.
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