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Wednesday, March 29, 2000

Mauna Kea team
finds the smallest
planets yet beyond
our solar system

The discovery takes us a step
closer to finding a planet like
our own orbiting a sun like ours

By Gregg K. Kakesako


Two more planets -- which may be smaller in mass than Saturn -- have been discovered by scientists at W.M. Keck Observatory on Mauna Kea in the hunt for extra-solar planets.

The latest planets are far smaller than the planets that have previously been found orbiting suns beyond our solar system.

Saturn, the sixth planet in our solar system, is about nine times wider than Earth, but has only one-third the mass of its neighbor Jupiter. Of the 30 planets previously found around stars like Earth's sun, all have been Jupiter-sized or larger.

The finding was made by Geoff Marcy of San Francisco State University and the University of California at Berkeley; Paul Butler of the Carnegie Institution of Washington; and Steve Vogt of the University of California at Santa Cruz, using the 10-meter Keck I telescope.

In a written statement, Marcy said that searching for planets orbiting distant stars is "like looking at a beach from a distance."

"Previously we only saw the large boulders, which were Jupiter-sized planets or larger," he said. "Now we are seeing the 'rocks,' Saturn-sized planets or smaller."

Sighting Earth-sized objects, said Marcy, would be like seeing pebbles on that beach. Astronomers are not yet able to do that.

One planet, with at least 80 percent the mass of Saturn, is orbiting 3.8 million miles from the star HD-46375, 109 light years away in the constellation Monoceros.

Another planet, with 70 percent of Saturn's mass, was found 32.5 million miles from the star 79 Ceti (HD16141), 117 light years away in the constellation Cetus.

The planets are presumably gas giants, the scientists say, made mostly of primordial hydrogen and helium, rather than the rocky materials that make up Earth. They orbit so close to their parent stars that they are extremely hot and not conducive to life.

The planet orbiting 79 Ceti has an average temperature of 1,530 degrees; while the planet orbiting HD46375 has an average temperature of 2,070 degrees.

The planets probably formed at a farther distance from the star, the scientists say, where they accumulated cool gas and then migrated into their present orbits.

Discovery of the Saturn-sized planets, however, supports a theory that planets such as those in Earth's solar system formed around many stars in the universe. It also supports the theory that most planets are relatively small, such as Earth, Mars and Venus.

The planets are not actually seen by astronomers. Instead, they measure the gravitational effect of planets on their star.

As a planet orbits, it causes the star to wobble very slightly. By measuring this wobble, scientists can detect the presence and size of a planet.

Astronomers have used this technique to catalog at least 21 extrasolar planets. The group is searching some 1,100 stars within 300 light-years of Earth to find evidence of planets. A light-year is the distance that light travels in a year in a vacuum, about 6 trillion miles.

Other astronomy groups are also searching and have found additional extrasolar planets.

The Associated Press contributed to this story.

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