Planet discovered using a new detection technique

University Park, Pa. -- A team of scientists, including two Penn State astronomers, have used an innovative new technique to discover a Jupiter-sized planet orbiting a nearby star.

The planet initially was detected using an instrument called the Exoplanet Tracker (ET) and may herald an era where the searches for such planets will become much more efficient. The discovery was announced at the recent meeting of the American Astronomical Society in Washington, D.C.

"In the last two decades, astronomers have searched about 3,000 stars for new planets," said Jian Ge, lead scientist on the study, who until recently was an astronomer at Penn State and now is professor of astronomy at the University of Florida. "Our success with this new instrument demonstrates that we soon will be able to search stars much more quickly and cheaply -- perhaps revealing as many as a couple of hundred thousand stars in the next two decades."

The initial design for ET was begun while Ge was an assistant professor of astronomy at Penn State from 2000 to 2004. Lawrence Ramsey, the head of Penn State's department of astronomy, and Donald Schneider, a professor in the department, also participated in the discovery of the new planet.

What makes Ge's team's discovery so interesting is ET's design; the instrument measures the velocity of stars to very high accuracy by using an interferometeric technique first proposed by in 1997 by Lawrence Livermore National Lab physicist David Erskine. This new approach has two important advantages over current techniques: lower cost and dramatically improved efficiency. ET is much smaller and less expensive than current instruments employed in planet surveys. Plus, as a result of ET's improved efficiency, astronomers can use it to examine fainter stars or they can use it with smaller telescopes to search for new planets.

As with most previous planet discoveries, the new planet was identified by its gravitational influence on its parent star. The velocity of the star changes by approximately 300 miles per hour every 4.1 days, the orbital period of the planet. Scientists measured these regular motions by examining the spectra of the light from the star.

This regular "wobble" in the velocity of stars is the principle used to identify the vast majority of extrasolar planets that have been found since 1992, when the first planet outside of our solar system was found by Alexander Wolszczan, Penn State's Evan Pugh professor of astronomy.

The planet was identified tentatively in ET observations taken with a 36-inch telescope at the Kitt Peak National Observatory near Tucson, Ariz., in early 2005. The initial 28 observations indicated that the star, located in the constellation of Virgo, might possess a planet. Additional observations were obtained with ET and the High Resolution Spectrograph of the Hobby-Eberly Telescope (HET) in late 2005. The HET measurements had the highest accuracy and were crucial in determining the precise period of the planet's orbit.

"One nice aspect of this result was that the HET -- the telescope upon which Jian Ge first used an early ET prototype in 2003 -- provided the conclusive evidence for the existence of the first ET-based planet discovery," remarked Larry Ramsey, who, along with former Penn State professor Daniel Weedman, developed the concept for the HET. In addition to Ge's group in Florida and Ramsey and Schneider at Penn State, scientists at the University of Texas, Tennessee State University, the University of California and the Institute of Astrophysics in Spain's Canary Islands were involved in the discovery.

"The performance of ET promises a bright future in planet detection," Schneider said. In addition to the increased efficiency and lowered cost, an enhanced version of ET, which has the ability to obtain simultaneous measurements of tens of stars, was tested successfully in 2005 at the 100-inch Sloan Digital Sky Survey Telescope at the Apache Point Observatory in New Mexico. "We are very excited by the new science capabilities that have been enabled by the interferometric technique," said Ge. "I believe that we are embarking on a new era in extrasolar planet discovery."

The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, Penn State, Stanford University, Ludwig-Maximilians-Universitat Muenchen and Georg-August-Universitat Goettingen. The telescope is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.