SETI: Search for ExtraTerrestrial Intelligence



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Extraterrestrial Life and Intelligence

Who's out there? Are we alone in the universe?
Scientists involved in SETI — the Search for ExtraTerrestrial Intelligence — are using modern technology to search for the answer to this fundamental questions.
They listen for a signal from space. This arises more questions: How do we know if a signal is from ET? And: what happens if we find something?

There is more than science fiction and the X files to the search for extraterrestrial life and intelligence.

Over the last years, scientists have developed a theory of cosmic evolution that predicts that life is a natural phenomenon likely to develop on planets with suitable environmental conditions. Scientific evidence shows that life arose on Earth relatively quickly, suggesting that life will occur on similar planets orbiting sun-like stars. With the recent discoveries of extrasolar planetary systems, and the suggestive evidence that life may once have existed on Mars, this scenario appears even more likely.

The central question of SETI science is not: "Is someone hiding aliens?" But rather: "What is Drake equation ?"
This equation has played a more crucial role in SETI than an entire season of X files broadcasts ...

This equation aims at roughly estimating the number of (technological) civilizations that might exist in the space.

In 1961, while working as a radio astronomer, Frank Drake conceived an approach to bound the terms involved in estimating the number of technological civilizations that may exist in our galaxy. The Drake Equation identifies specific factors thought to play a role in the development of such civilizations. Although there is no unique solution to this equation, it is a generally accepted tool used by the scientific community to examine these factors.

N = R* × fp × ne × fl × fi × fc × L

= The number of communicative civilizations The number of civilizations in the Milky Way Galaxy whose radio emissions are detectable.
= The rate of formation of suitable stars The rate of formation of stars with a large enough "habitable zone" and long enough lifetime to be suitable for the development of intelligent life.
= The fraction of those stars with planets The fraction of Sun-like stars with planets is currently unknown, but evidence indicates that planetary systems may be common for stars like the Sun.
= The number of "earths" per planetary system All stars have a habitable zone where a planet would be able to maintain a temperature that would allow liquid water. A planet in the habitable zone could have the basic conditions for life as we know it.
= The fraction of those planets where life develops Although a planet orbits in the habitable zone of a suitable star, other factors are necessary for life to arise. Thus, only a fraction of suitable planets will actually develop life.
= The fraction life sites where intelligence develops Life on Earth began over 3.5 billion years ago. Intelligence took a long time to develop. On other life-bearing planets it may happen faster, it may take longer, or it may not develop at all.
= The fraction of planets where technology develops The fraction of planets with intelligent life that develop technological civilizations, i.e., technology that releases detectable signs of their existence into space.
= The "Lifetime" of communicating civilizations The length of time such civilizations release detectable signals into space.

(information from


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