nih.gov
SETI and Astrobiology
The search for intelligent life on worlds beyond Earth represents the most romantic and publicly accessible aspect of the search for life, yet is perhaps the most problematic. No as yet known remote-sensing technique can detect the presence of intelligent versus complex life forms, other than by listening for electromagnetic forms of communication leaking from or deliberately sent from another world.11. J. Tarter, “The Search for Extraterrestrial Intelligence (SETI),” Annual Review of Astronomy and Astrophysics 39: 511-548, 2001. Human civilization has put chlorofluorocarbons in the stratosphere, which are demonstrably the product of a technological civilization but require high spectral resolution to detect. Further, the damaging effects on the stratospheric ozone layer of these compounds imply that a civilization would do this only for a minuscule amount of time, several decades, making detection of such compounds very unlikely.
