TSU Helps to Discover Very Young Planet

Newswise — A new team of astronomers from Tennessee State University, the University of Florida, the Institute of Astrophysics in Spain's Canary Islands, Pennsylvania State University, and the University of Texas have discovered one of the youngest extrasolar planets found to date with a new device that promises to accelerate the discovery of planets outside our solar system.

"In the last two decades, astronomers have surveyed about 3,000 stars for new planets," said Jian Ge, a professor of astronomy at the University of Florida, who built the instrument. About 160 planets have been discovered since 1995 around those 3,000 stars. "A newer version of our instrument that is under development should allow us to survey 100,000 stars or more in the coming decade," said Professor Ge.

The new planet was announced this month at the annual meeting of the American Astronomical Society in Washington, D.C. The planet orbits the star HD 102195, which lies at a distance of about 90 light years from Earth toward the constellation Virgo. It completes an orbit around the star in less than five days, meaning that it is very close to its parent star and is too hot to support life.

"This new planet is especially interesting because it orbits a star just 600 million years old," said Greg Henry, an astronomer at Tennessee State University who participated in the discovery. That is very young compared with the Sun's 4.6 billion year age and the ages of most other planet-hosting stars. "Finding more planets around young stars will give us insight into how planetary systems, including our own solar system, formed and evolved over time," said Henry.

Ge's new instrument that detected the planet around HD 102195 was built based on a concept proposed by David Erskine at Lawrence Livermore National Lab in 1997. Like the instruments that have detected most of the 160 known extrasolar planets, the new instrument, which Ge calls the Exoplanet Tracker or simply ET, detects the presence of a planet in orbit around a star by observing the wobbles of the star caused by the orbiting planet. However, unlike other instruments that use a spectrograph to measure the subtle Doppler shifts in the star's light caused by the wobble, Ge's instrument is based on an interferometer. The ET can make more efficient use of the light collected from the star by a telescope and thus observe fainter, more distant stars or make use of smaller telescopes, which are more easily accessed. In addition, modifications to the ET will soon allow the instrument to measure as many as 100 stars simultaneously. This should greatly accelerate the pace of extrasolar planet discoveries.

However, astronomers know that planet discovery is never easy. In the latest find, astronomers went to great lengths to ensure they were actually "seeing" a planet.

"That's because the star, which has about 80% of the Sun's mass, retains much of its youthful rotation speed, which makes it capable of generating strong magnetic fields and associated dark starspots," said Henry. "These are similar to the magnetically generated sunspots on our own Sun, and they can mimic the presence of a planet in orbit around the star," he added.

To check against this possibility, Henry used one of the robotic telescopes in Arizona operated by Tennessee State University to measure the star's brightness from night to night. As expected for a young star, he discovered the star's brightness was changing as dark starspots rotated into and out of view. "The rotation period of the star derived from these brightness measurements is about 12 days," said Henry. "Because the planetary orbital period is much different than the star's rotation period, the dark starspots cannot be causing the false appearance of a planet. The planet appears to be real."

Photo: Attached is an artist's rendering of the young planet orbiting its star.

Tennessee State University is a major, comprehensive urban land-grant institution which offers 45 bachelor's degrees and 24 master's degrees. Doctoral degrees are offered in six areas: biological sciences, psychology, public administration, curriculum and instruction, administration and supervision, and computer information systems engineering.