A mission, currently under study, that would form an important part of NASA's Origins Program. TPF would search for small, terrestrial-type planets around nearby stars and analyze the spectra of these worlds for the chemical signatures of life. Two different approaches are being considered to achieve the same goal, namely, to block the light from the parent star in order to see its much dimmer planets—a feat likened to finding a firefly near the beam of a faraway searchlight. One of the technologies under study involves an infrared interferometer, possibly consisting of four 8-m telescopes, with a total surface area of 1,000 m2. The interferometer would use a technique called nulling to reduce the starlight by a factor of one million (see nulling interferometry), thus enabling the detection of the very dim infrared emission from small planets. The other kind of instrument under review is a visible light coronagraph, which would consist of a large optical telescope, with a mirror three to four times bigger and at least 10 times more precise than the Hubble Space Telescope. The telescope would have special optics to reduce the starlight by a factor of one billion, thus enabling astronomers to detect the faint planets. A final choice of strategy is expected by 2005 or 2006 and a launch in about 2012.
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