Saturday, November 13, 1999

'Astounding astronomy first: Keck scope spots planet orbiting distant star

A Keck telescope team delivers
proof of a body orbiting a
star like our own

By Lori Tighe


Never before have astronomers witnessed direct proof of a planet outside our solar system -- until now, based on observations made through the eye of the Big Island's Keck I telescope.

A massive planet was discovered in the Pegasus constellation about 859,000 billion miles or 153 light years away, scientists said. It is a gas giant like Jupiter, but even bigger and more gaseous. Its radius is 60 percent greater than Jupiter's, but it is one-third less dense.

"It's an astounding discovery and a quantum leap forward in knowledge," said Andrew Perala, spokesman for the W.M. Keck Observatory on Mauna Kea.

"It's an amazing time to be alive. For the first time in centuries, we have been able to prove the existence of another planet outside our solar system."

The discovery was made by the world's "premier planet-hunting team" of Geoffrey Marcy, an astronomy professor at the University of California at Berkeley, and Paul Butler, of the Carnegie Institute of Washington's Department of Terrestrial Magnetism.

They used a combination of instruments that is extremely precise and can detect objects 600 trillion miles away that are moving three meters per second.

"This is the first independent confirmation of a planet, and it also gives us the first-ever measure of the size of one of these planets," Marcy said.

The planet's star, classified as HD 209458, is about the same age, color and size as our own sun.

Marcy and Butler's research, to be published in the Astrophysical Journal, is supported by NASA, the National Science Foundation and Sun Microsystems.

"With this one, everything hangs together," Marcy said. "This is what we've been waiting for."

Up until now, scientists have only inferred the existence of about two dozen extra-solar planets by the "wobble" of their stars. A star moves back and forth off its center of gravity when a planet orbits it. Jupiter, for example, pulls the sun off the center of its gravity 12 meters per second.

It takes Jupiter 12 years to go around the sun, Perala said. "This planet takes four days to orbit its star," he said. "It's a massive planet very close in to the star."

Scientists have seen its star dim as the planet passed.

When the scientists at Mauna Kea first discovered the wobble on Nov. 5, they calculated the planet's orbit and mass. Then they told colleagues in the Patagonia mountains of southern Arizona to watch for the star to "blink" as the planet orbited it.

The star indeed dimmed 1.7 percent four days later, at the moment predicted, proving the planet's existence, Perala said.

"This planetary transit occurred at exactly the time predicted from Marcy's observations, confirming absolutely the presence of a companion," said astronomer Greg Henry, with the Center of Excellence in Information Systems at Tennessee State University. Henry confirmed the discovery with telescopes at the Fairborn Observatory in Arizona.

"This says that our indirect evidence for planets, the change in radial velocity of the star, really is due to planets," Henry said. "We've essentially seen the shadow of the planet."

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