Viewing in the infrared, these images will be of a spectrum of colors representing the different chemicals in the planet's atmosphere.
"What we are looking for is an atmosphere out of chemical equilibrium," said Fridlund. "Currently the Earth's atmosphere is out of such an equilibrium through its oxygen."
Scientists believe that without life, all free oxygen in the atmosphere would disappear within just four million years because it reacts so easily with other chemicals. So if scientists detect a planet with a lot of oxygen, it could be a sign that it harbors life.
Other signatures the scientists hope to search for include water vapor and carbon dioxide. Later, they might scan for chlorophyll, the chemical compound found in plants which allows plants to convert solar energy from the sun into energy through the process known as photosynthesis. The detection of chlorophyll in space would provide strong evidence of active photosynthesisan extraterrestrial life.
As Darwin and TPF scientists plan for their missions to launch sometime in the middle of the next decade, the SETI Institute is moving forward with plans in collaboration with the University of California at Berkeley to build a massive radio telescope known as the Allen Telescope Array, which will be dedicated to SETI.
Currently the SETI Institute is limited to available time on radio telescopes, which is mostly allocated to other kinds of radio astronomy. The SETI Institute only gets three or four weeks of observation time each year.
The array will be a 350 dish interferometer and will simultaneously conduct SETI research and radio astronomy, said Edna Devore, the SETI Institute's director of education and outreach. The array is anticipated to be online in 2005.
The institute is also partnering with NASA's Ames Research Center in Moffett Field, California, on the Kepler Mission, which will launch in 2007 and for the first time allow scientists to search for Earth-sized planets in orbit around distant stars.
"The results of the Kepler Mission is essential for NASA and ESA in planning Darwin and TPF because Kepler will discover that planets like Earth are common or rare," said Devore.
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