Other SETI    updated Apr 7, 2016  D. Carrigan (carrigan@fnal.gov - subject line must be sensible)

(My SETI interest is not funded by Fermilab or the U. S. Department of Energy. This portion of the site is needed to illustrate other interconnections related to Fermilab.)
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Cosmic archaeology approach to SETI

Fermi paradox: It 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 Webb discusses the Fermi paradox in some detail.

Dyson sphere: Dyson 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.

Kardashev 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 extraterrestrial intelligence) 

Meteors: 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.

Extrasolar 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.

Panspermia: 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 investigators.

Surprisingly, 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, etc.