planets might harbor life? Scientists can't say for sure,
with only the Earth as an example. But the two main planetary
ingredients for life seem to be liquid water and time.
boils off planets too near their stars, but freezes solid
on those too far away. The "life zone" is the region around
a star in which planets can maintain liquid water. The size
and location of this zone depends on the size and temperature
of the star. Hot stars have wider zones than their cooler
counterparts. But the hotter the star, the shorter its life
span. The second requirement for life rules out these short-lived
planets likely orbit stars similar to our sun.
took about a billion years before even the simplest life forms
debuted on this planet. Another three billion years or so
elapsed before intelligence evolved. Very hot stars, which
can burn out after only one million years, aren't around long
enough for life to arise on their surrounding planets.
out the hottest and the largest stars, as well as the smallest
and the coolest, the search for life must focus on stars of
average size and temperature. In other words, stars like our
With the Terrestrial
Planet Finder (TPF), NASA scientists may one day have
a tool for detecting life-giving elements on faraway planets.
Called "the most ambitious science mission ever attempted
by NASA," by the National Academy of Sciences, this special
telescope will use light to gather data about astronomical
bodies. Among other things, the TPF will look for any Earth-sized
planets within about 50 light years of our own. It will then
determine which of these planets- if any- lie in the life
zones of their parent stars, and detect if any of the "signposts
of life," such as chlorophyll, are present in the atmosphere.
NASA is scheduled to launch the TPF in 2011.
from the TPF will help fill in many of the unknowns in Drake's
Equation. But, according to Dr. Charles Beichman, Chief Scientist
of the Origins Program, the success of the TPF depends only
"on the first two terms of Drake's Equation," says Beichman.
"SETI jumps right to the end."
"the most ambitious science mission ever attempted by
NASA," the TPF will use light to gather data about astronomical
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