June 29, 1998 A planet has been discovered orbiting one of the nearest stars to our own sun, a San Francisco State University (SFSU) astronomer reported this week.
The nearby star, known as Gliese 876, is only about a third as massive as the sun, and the discovery of a planet orbiting a small neighboring star increases the likelihood that planets are common near our solar system, throughout the galaxy, and beyond.
“This star is by far the lowest mass star for which a planet has been found,” said Geoffrey Marcy, University Distinguished Professor of Science at SFSU and an adjunct professor of astronomy at UC Berkeley. “This suggests that planets are common – independent of the mass of the star.” Marcy has discovered or co-discovered most of the 12 planets so far detected beyond our solar system.
The discovery was reported June 22 at the International Astronomical Union Colloquium, meeting in Victoria, British Columbia.
The team that made the new discovery includes Paul Butler, an astronomer at the Anglo-Australian Observatory who, as a graduate student and post-doctoral scientist with Marcy at SFSU helped develop the technique that made the detection possible.
Other team members are: Steven Vogt, professor of astronomy at University of California at Santa Cruz, Debra Fischer, a post-doctoral researcher with Marcy at SFSU, and Jack Lissauer, of the NASA Ames Research Center in Mountain View, California.
Only hours after Marcy announced the discovery, a European team confirmed it. Both research groups used similar techniques, detecting the presence of planets indirectly – from their effect on the motion of the star they orbit. The astronomers look for a telltale wobble in the star’s motion.
Gliese 876 is only 15 light-years from Earth, and it is both the closest and smallest star yet detected with an orbiting planet. Its planet is some two times the mass of Jupiter and takes 61 days to make a complete orbit. Its average distance from Gliese 876 is less than the closest approach our innermost planet Mercury makes to the sun.
The star’s faintness made it difficult to analyze, Marcy said. Only use of the massive Keck Telescope atop Hawaii’s Mauna Kea provided adequate resolution.
He noted that the planet’s orbit is quite elongated, or eccentric, relative to the more circular orbits of planets in our solar system. This, he said, reopens a mystery of what determines the shape of a planet’s orbit. It may suggest that planets can gravitationally “slingshot” off each other, and sling themselves into wild orbits.
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