Cosmic archaeology approach to
is relatively easy to move around the galaxy at one ten
thousandth of the speed of light if you are patient. Fermi
may have noticed this in the fifties and asked why there
weren't aliens on earth. A recent book by Stephen
the Fermi paradox in some detail.
suggested that all the energy from a star could be
harnessed by breaking up the planets around the star to
form a loose shell. A Dyson Sphere would be an
archaeological signal of extrasolar intelligence.
There have been a number of searches
for Dyson Spheres.
classified astronomical sources according to the
potentially available energy for SETI signaling. A Type I
Kardashev civilization could utilize all the energy
available from a planet such as the earth. A type II
Kardashev would exploit all the energy from a star (a
Dyson Sphere could be one approach). A Type III
civilization could harness all the energy from a galaxy.
Jim Annis at Fermilab has searched for Type III
civilizations using light distributions from galaxies.
Lemarchand has produced several
comprehensive reviews covering a number of cosmic
archaeological signatures for SETI.
Possible signals of
extraterrestrial life (not necessarily a sign of
Based on their composition certain meteors found in
Antarctica can be shown to come from Mars. One analyzed by
McKay, et al. has controversial evidence for Martian life.
planetary atmospheres: Several extrasolar
planetary atmosphere have already been observed.
There is a very substantial step from a first observation
to confidence that one is observing an atmosphere
generated by life or even hospitable to it. Burrows
has recently reviewed some of the difficulties in seeing
planetary extrasolar atmospheres.
This is the idea that life may have traveled between stars
perhaps as spores carried in cosmic dust or cosmic grains.
Hoyle and Wickramasinghe have been among the most active
a one centimeter diameter sphere of DNA would contains an
amazing 1020 bytes of information. For the
relatively "slow" speeds needed to escape a star (10-4
of the speed of light) the information cost per bit are
comparable to electromagnetic signaling. The problems
include the associated rockets, shielding, guidance,