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The Question
(Submitted September 24, 1997)
What are the chances of life existing outside our solar system?
The Answer
This is a question that astronomers first started to quantify in the
early 1960s. In 1961, a radio astronomer named Frank Drake developed
an equation to stimulate discussion of the Search for Extraterrestrial
Intelligence (SETI). This equation, which is now called the Drake
equation, states that the number of communicating civilizations in our
galaxy likely depends on a number of factors which must combine to
yield a habitable planet where life has the chance develop to a certain
level of technological know-how. These factors include the rate of
formation of stars like the Sun, the fraction of those with planets,
the fraction of Earth-like planets, the fraction of such planets where
life develops, the fraction of those where the life becomes
intelligent, the fraction of intelligent species who can communicate in
a way we would detect, and the lifetime of the communicating
civilizations. As you may imagine, there is a lot of debate about
reasonable values for most of these factors. As we learn more about
the likelihood of planets around other stars, we are able to better
estimate one of these parameters. For the other parameters, the
estimates vary widely. Frank Drake's own current estimate puts the
number of communicating civilizations in the galaxy at 10,000.
You can find out more about the Drake Equation from
http://www.setileague.org/general/drake.htm
http://seds.lpl.arizona.edu/~rme/drake.html
Cheers,
Padi Boyd
for the Ask an Astrophysicist
Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html
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