Philosophical Society of Washington

(Discovery of) Extrasolar Planets

R. Paul Butler
Carnegie Institute of Washington

2133rd Meeting Abstract
Friday, September 21, 2001 at 8:15 P.M.


Over the last six years planets have been discovered around 70 nearby Sun-like stars. All of these planets have been revealed by the gravitational wobble they impose on their host stars. Our group has found about two-thirds of these planets, including the first system of multiple planets orbiting a Sun-like star, the first two sub-saturn mass planets, and the first transit planet.

The planets detected to date have profoundly challenged the theories of planet formation, including Jupiter-mass planets in very small (4 day) orbits, and Jupiter-mass planets in extremely eccentric orbits. Only two of the planetary systems discovered to date are even remotely similar to the Solar System. Now that planets have been detected, we would like to know what fraction of stars have planets, what fraction of planetary systems are similar to the Solar System, and how many other types of planetary systems exist. Our current goal is to survey all 2,000 Sun-like stars out to 150 light-years. We are currently observing 1,200 stars with the Lick 3-m (California), Keck 10-m (Hawaii), and the 3.9-m Anglo-Australian Telescopes. Next year we will expand these surveys with the 6.5-m Magellan Telesccope.

The Keck, Lick, and Anglo-Australian surveys are the only active programs capable of detecting "Solar System-like" planets (i.e. Jupiter and Saturn-mass planets) beyond 4 AU. By 2010 these surveys will provide a first planetary census of nearby stars and allow us to estimate the ubiquity of planetary systems and of "Solar System" analogs.

About the Author:

R. Paul Butler received a B.A. in Physics (1985) and B.S. in Chemistry (1986) and a M.S. in Physics (1989) from San Francisco State University. He received a Ph.D. in Astronomy (1993) from the University of Maryland. He has previously served as a Research Scientist at San Francisco State University, a Visiting Research Fellow at U.C. Berkeley, and a Staff Astronomer at the Anglo-Australian Observatory. He is presently a Staff Scientist at the Carnegie Institution of Washington Department of Terrestrial Magnetism. Honors include the ABC News Person of the Week, International Astronomical Union Bioastronomy Medal, and the National Academy of Sciences Henry Draper Medal.

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