The Terrestrial Planet Finder (TPF) will find earth's cousins: planets potentially suitable for life
Probably the most ambitious of the projects recommended by the Astronomy and Astrophysics Survey Committee, the Terrestrial Planet Finder (TPF) will offer humanity the means to discover Earth-like planets orbiting other stars. Still in a conceptual stage, one version of the TPF would consist of four infrared-observing telescopes, each with a 3.5-meter mirror and spaced as much as a kilometer apart. So that they will be shielded from radiation that would interfere with their observations, the telescopes will orbit the Sun far from Earth's interfering infrared radiation. The telescopes will deploy panels to keep the Sun's rays from warming them, so that they can maintain temperatures close to 400 degrees below zero Fahrenheit and thus largely avoid emitting their own infrared radiation. The infrared domain offers better prospects than visible light for revealing an Earth-like planet. In this spectral region, a typical star outshines an Earth-like planet by a factor of only one million, rather than by a factor of one billion at visible wavelengths. By using a technique called nulling interferometry, the TPF could overcome this ratio of one million, which threatens to drown a planet's firefly light in the glare of the nearby stellar searchlight. Nulling interferometry effectively darkens the brilliant, pointlike starlight by diverting it along two paths that cancel each other, leaving a nearby planet visible.When not studying nearby stars for signs of extrasolar planets like our own, the TPF will observe other cosmic objects with an angular resolution a hundred times better than that of any previous instrument. This resolution will allow the TPF to study planetary systems in formation and star-forming regions in distant galaxies with a stunning clarity. Among other achievements, the TPF's high-resolution capability could allow it to verify the current hypothesis that the phenomena of quasi-stellar radio sources (quasars) and active galactic nuclei arise from matter swirling into black holes at the centers of galaxies.
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