The Drake equation states that:
N = R* X fp X fe X fl X fi X fc X L
where:
N is the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time
and
R* is the rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is average number of planets that can potentially support life per star that has planets
fl is the fraction of the above that actually go on to develop life
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of the above that are willing and able to communicate
L is the expected lifetime of such a civilization
This section attempts to list best current estimates for the parameters of the Drake equation.
R* = the rate of star creation in our galaxy
Estimated by Drake as 10/year. Latest calculations from NASA and the European Space Agency indicates that the current rate of star formation in our galaxy is about 6 per year. The Planck Institute for Extraterrestrial Physics in Germany notes, however, that our galaxy is not the biggest producer of stars and supernovae in the universe. [1]
fp = the fraction of those stars which have planets
Estimated by Drake as 0.5.
ne = the average number of planets (or rather satellites; moons may perhaps sometimes be just as good candidates) which can potentially support life per star that has planets
Estimated by Drake as 2.
fl = the fraction of the above which actually go on to develop life
Estimated by Drake as 1.
In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated fl as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth. Lineweaver has also determined that about 10% of star systems in the Galaxy are hospitable to life, by having heavy elements, being far from supernovae and being stable themselves for sufficient time. [2]
fi = the fraction of the above which actually go on to develop intelligent life
Estimated by Drake as 0.01.
Some estimate that solar systems in galactic orbits with radiation exposure as low as Earth's solar system may be more than 100,000 times rarer, however, giving a value of fi = 1×10-7.
fc = the fraction of the above which are willing and able to communicate
Estimated by Drake as 0.01.
L = the expected lifetime of such a civilization
Estimated by Drake as 10,000 years.
The value of L can be estimated from the lifetime of our current civilization from the advent of radio astronomy in 1938 (dated from Grote Reber's parabolic dish radio telescope) to the current date. In 2006, this gives an L of 68 years.
In an article in Scientific American, Michael Shermer estimated L as 420 years, based on compiling the durations of sixty historical civilizations. Using twenty-eight civilizations more recent than the Roman Empire he calculates a figure of 304 years for "modern" civilizations. Note, however, that the fall of most of these civilizations did not destroy their technology, and they were succeeded by later civilizations which carried on those technologies, so Shermer's estimates should be regarded as pessimistic.
The equation based on current lower estimates, therefore, is thus:
R* = 6/year, fp = 0.5, ne = 2, fl = 0.33, fi = 1×10-7, fc = 0.01, and L = 420 years
N = 6 × 0.5 × 2 × 0.33 × 1×10-7 × 0.01 × 420 = 8.316×10-7 = 0.0000008
It is worth noting that the order of magnitude in the revised equation is determined primarily by the new estimate for fi. Going back to the number estimated by Drake (1×10-2) the result also changes to 0.08.source:
http://en.wikipedia.org/wiki/Drake_equation
Topic: More Planets Found (Read 4060 times)