"Alien Worlds," David
Latham and his colleagues at the Harvard-Smithsonian Center
for Astrophysics use cutting-edge science to locate planets
beyond our own solar system. Until 1995, no one had ever found
an "extra-solar" planet, and only a handful is known today.
Yet, since the 1960's, scientists have been listening for
alien signals nonetheless.
What are the chances intelligent life exists beyond Earth?
In 1961, radio astronomer Frank Drake presented a means of
estimating the number of technological civilizations that
likely exist in the galaxy. The equation that bears his name
is thought to be among the most important of the 20th Century,
second only to Einstein's E=MC2. Drake's Equation factors together
all of the assumed conditions required for advanced civilizations
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Mathematics of Life
equals the number of civilizations in our galaxy with both
the brains and the tools to communicate with us. N*
is the total number of stars in the galaxy, estimated to be
between 100 and 200 billion.
represents the fraction of those stars with planets. Before
the 1995 discovery of the first extra-solar planet, astronomers
didn't have any idea what this number might be. Subsequent
surveys put fp
at about one percent. In a galaxy with 100 billion stars,
that's about one billion solar systems.
Drake was the first to listen for extraterrestrial radio
not every solar system is suitable for life. The term ne
stands for the number of these planets that are roughly "Earth-like,"
rocky, temperate and relatively stable. Scientists are just
beginning to collect the data needed to guess at a galaxy-wide
value for ne.
remaining variables are even harder to nail down. fl
denotes the fraction of these Earth-like planets on which
life has sprung out of the favorable conditions. Of those
planets that harbor life, only some, represented by fI,
will evolve an intelligent species. And only a fraction of
those intelligent species, fc,
will develop technology.
equation is thought to be among the most important of
the 20th Century, second only to Einstein's E=MC2 .
L is the lifetime of a
communicating civilization. How long can an advanced society
exist before political, economic or environmental problems
tear it apart? With such subjective variables, it's clear
that no single solution to Drake's equation exists. Nonetheless,
Drake and colleague Carl Sagan estimated there might be as
many as one million communicative civilizations in the Milky
Way. That figure, rough as it is, still compels researchers
at leading institutes around the world to search for planetary
needles in the galactic haystack.
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NASA, Melita Wade Thorpe