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             Annual Sagan Lecture              

Extrasolar Planets - Paul Butler - Carnegie Institution                           

Presented as part of the American Geophysical Union's 2003 Fall Meeting

           Friday, December 12th at 8:00 am

           Moscone West Conference Center

           Room 2002

           4th and Mission Streets

          San Francisco

                 None of the roughly one hundred hundred extrasolar planets found to date closely resembles the Solar System. Unlike the Solar System, most extrasolar planets are in eccentric orbits. The giant planets in the Solar System all orbit beyond 5 AU, while the known extrasolar planets (with one exception) all orbit within 4 AU, with several in extraordinarily small orbits with periods of days to weeks. Current state-of-the-art technology can only detect giant planets, with the most massive planets being the easiest to detect. Nonetheless the planet mass function rises toward lower masses down to the limit of detection incompleteness, below a jupiter-mass. There are almost no planets more massive than 5 jupiter-masses though these would be the easiest to detect. The planet bearing stars are significantly enriched in elements heavier than hydrogen and helium relative to both the Sun and nearby stars. NASA, the European Space Agency, NSF, and the European Southern Observatory are all focused on "next generation" planet detection technologies including giant ground-based 30 and 100 meter telescopes capable of directly imaging giant planets, space-based interferometers apable of detecting terrestrial-size planets in earth-like orbits, and space-based telescopes capable of directly imaging earth-like planets and taking their spectra. The first of these next generation instruments should be operating by the end of the decade, with first results coming in around 2015. The goal of our group is to survey all Sun-like stars out to 50 parsecs, a total of about 2,000 stars. At the time of this writing (September 2003) we are surveying 1,700 of these stars using the Lick 3-m (California), Keck 10-m (Hawaii), 3.9-m AAT (Australia) and 6.5-m Magellan (Chile) telescopes. Recent discoveries from our group include several systems of multiple planets, the only known transit planet, and the first sub-saturn mass companions, as well as two-thirds of all known extrasolar planets. Solar System analogs, Jupiter and Saturn--like planets orbiting beyond 4 AU, have not yet been discovered. These elusive planets will begin emerging from our existing surveys before the end of this decade. By 2010 our surveys will provide a first planetary census of nearby stars, allowing us to estimate the ubiquity of planetary systems and of "Solar System" analogs, and thus put the Solar System in a Galatic perspective for the first time.











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