College of Science & Engineering Alumni Newsletter

Spring 1997

Planet Hunter: R. Paul Butler
“When Geoff Marcy, professor of physics here, said to me, ‘I think we can find planets around other stars,’ this was one of the most courageous, audacious, visionary, and maybe even insane things I had ever heard. This one sentence changed my life.”—Paul Butler, BS, MS, Physics and Astronomy

Paul Butler was inducted into the Alumni Hall of Fame by San Francisco State University's Alumni Association on February 13th. For the past ten years Paul has collaborated with SFSU Physics and Astronomy Professor Geoffrey Marcy in a search for planets orbiting nearby Sun-like stars. Over the past year Paul and Geoff have received international recognition for their discoveries of six planets and their confirmation of two others. These are the first eight planets found around other stars outside of our solar system. You may have seen the pair on a recent NOVA presentation, “Search for Alien Worlds,” and they have also been the subject of front-page articles in the New York Times and Washington Post.

Butler, 36, a post-doctoral researcher at San Francisco State with a joint appointment at the University of California at Berkeley, began developing the technology to search for planets in the fall of 1986 while a master's student in the Department of Physics and Astronomy at SFSU. Prior to that, Butler earned undergraduate degrees in both physics and chemistry at San Francisco State. In 1993, he earned a Ph.D. in astronomy from the University of Maryland.

Marcy and Butler have monitored 120 stars at the Lick Observatory since the summer of 1987. These are the nearest Sun-like stars, lying within 100 light years of the our solar system. Planets are revealed from the gravitational perturbations they impose on their host stars. For example, Jupiter causes the Sun to "wobble" with a velocity of 12 meters per second. Marcy and Butler have developed the world's most precise Doppler technique, capable of measuring velocity changes as small as 3 meters per second (human walking speed!). In January of last year, Butler and Marcy's search began to pay off when they discovered two new Jupiter-sized planets, one that could potentially contain the requisite elements for life. "When I first saw the data come up, I was completely blown away," recalled Butler. "It knocked me off my chair."

Marcy agreed: "The importance of these discoveries is mindblowing. It opens a whole new subfield of astrophysics—the study of solar systems. We can now begin to comparatively study planetary systems and to put our own in the context of others."

Their most recent discovery is a remarkable new planet around a Sun-like star, 16 Cygni B, 85 light years from Earth. This planet orbits its star with the most extreme eccentricity, or oblong shape, ever found for any planet. This new planet dismantles the long-held theory that other planets in the universe would all have nearly circular orbits. The newest planet was discovered independently by two teams: Marcy and Butler at San Francisco State, and Drs. Bill Cochran and Artie Hatzes from the University of Texas.

Far from resting on his laurels, Paul has recently quadrupled his work load. Along with the ongoing Lick Observatory Planet Search of 120 stars, Marcy and Butler have started a much larger planet survey using the world's largest telescope, the 10 meter Keck, in Hawaii. The planned duration of this project is one Jupiter orbital period, or 12 years. Paul also continues his research on giant pulsating stars, and the further development of improved Doppler velocity techniques. Paul's other interests include traveling and jazz, especially the music of John Coltrane.

For the latest on Butler and Marcy's planet hunt, including Doppler velocity curves, a discussion of the Doppler technique, the current target list of stars, and research papers to download, visit their website, SFSU Planet Search Project.

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Updated by Lannie Nguyen-Tang on August 3rd, 2000