What is SETI?
SETI is the acronym for the Search for Extra-Terrestrial Intelligence. The SETI Institute conducts research that seeks evidence of life on exoplanets orbiting other stars, as well as on other bodies in our solar system.
In 1961, Dr. Drake proposed the Drake Equation to stimulate interest in listening for radio signals from alien civilizations, although contemporary telescopes could not detect any exoplanets; SETI was founded to take on that task.
What does the Drake Equation Predict?
The Drake Equation relies on the accuracy of its parameters, and experts have been adjusting those estimates since the equation was first proposed.
- R* = 15 new stars per year; that is about double some earlier estimates.
- fp might be 0.5. Prior to the discovery of the first exoplanet, conservative estimates may have been much less than 0.1.
- ne = 2.5 to 4, based on our solar system. Venus is questionable; Earth and Mars are obvious; and moons such as Titan or Europa are possibilities.
- fl is 1/3, based on our solar system. Finding life or fossils on Mars would double this parameter.
- fi = 0.5 to be conservative. The currently known facts in our solar system would set “fi = 1″, since Earth is the only known planet with life and it has intelligent life. (If one argues that whales, dolphins, some birds and primates are also intelligent, then “fi > 4″ would be reasonable).
- fc = 0.5 to be conservative. Again, our Earth indicates “fc = 1″ since we broadcast radio transmissions.
- L = 1,000 is a hopeful view since it’s been about 110 years since the first radio transmissions. Will a technologically-advanced civilization destroy itself soon after developing telecommunications capabilities, or might it find better ways to communicate without broadcasting radio signals into space?
Using these parameters, the Drake Equation estimates that there are some 1,547 planets with civilizations transmitting radio signals that we might detect.
Does the Drake Equation have Rivals?
Naturally the Drake Equation has been challenged from several directions.
One approach is to ask how many alien civilizations might be actively exploring the galaxy. If one assumes that every civilization that can communicate will also develop interstellar travel, at least for robot probes as sophisticated as Voyager, then some 1,547 civilizations may be involved. A further assumption is that such civilizations would automate manufacturing subsequent probes, so that the effort would grow without practical bounds.
Eventually that line of reasoning concludes, “Since we have not yet been visited by alien explorers, there must be none at all.”