for National Geographic News
The search for planets with extraterrestrial life has gotten a new tool: an "ID chart" that scientists will use to compare alien worlds with Earth as it has appeared over the eons.
Many astronomers say they expect to find Earthlike planets soon, when better technology enables them to spot small, distant worlds.
(See National Geographic magazine's "Search for Other Earths.")
"We believe that within 10 or 15 years we'll find the first planet that's Earthlike," said Lisa Kaltenegger, an astrophysicist with the Harvard-Smithsonian Center for Astrophysics (CfA).
"Then the question will be, Is this a habitable planet?"
To answer that question Kaltenegger and colleagues have created a historical model of the only planet known to have intelligent lifeEarth.
"We created a fingerprint for the Earth throughout its evolution so that we can compare it to any planet that we find and, we think, say if there is life on it," Kaltenegger explained.
(CfA scientists also announced today the discovery of the largest planet ever found.)
"Fingerprint" of Extraterrestrial Life
The gases in a planet's atmosphere provide the unique fingerprint for such a comparison.
Scientists examine atmospheric conditions on worlds too distant to visit by using visible and infrared light.
The mix of gases in a planet's atmosphere creates a unique spectruma colorful fingerprintthat reveals conditions on the planet's surface.
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