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Team Discovers New Solar Systems New Characteristics Challenge the Usual Definition of Planets

By Usha Lee McFarling

A California-based team that is dominating the difficult chase to find planets circling other suns announced Tuesday that it has found the most bizarre solar systems yet.

One of the systems contains a monstrous body 17 times the mass of Jupiter -- so massive it stretches the notion of what a planet may be.

The other system contains two planets “humming in harmony” as they spin in orbits so synchronized that scientists compare them to nested Russian dolls.

“Both planetary systems are quite unique, and a bit frightening,” said Geoffrey W. Marcy, an astronomer at the University of California, Berkeley, who leads the planet-hunting team that has detected about two-thirds of the 55 extrasolar planets found since 1995.

“This shakes my confidence that I knew ... the full range of planets,” Marcy said.

Astronomers cannot see the planets directly because, unlike stars, they do not give off their own bright light. Instead, the scientists use telescopes to detect the gravitational tug of the planets that causes the stars they orbit to wobble.

What astronomers see are changes in the spectra of light given off by stars as they move back and forth. This “Doppler signature” is the same phenomenon that causes a fire-truck siren to wail at different frequencies as the vehicle moves past.

Current technology -- even the 10-meter Keck telescope, the world’s largest -- allows astronomers to detect only larger planets, because the larger pull they exert on stars is more visible.

One planet with the mass of Saturn was found in 1999, and most of the others have been two or three times the mass of Jupiter. Still, these are far smaller than the newly detected behemoth, which is at least 17.2 times the mass of Jupiter -- and may be 40 times.

(Astronomers can only approximate the mass. And, in a counterintuitive twist, planets that are many times the mass of Jupiter may actually be smaller in size because of the stronger effect of gravity pulling material toward the planets’ centers.)

“This is the whopper,” R. Paul Butler, an astronomer at the Carnegie Institute of Washington and longtime collaborator of Marcy, said at a briefing at the annual American Astronomical Society meeting here. “This is literally off our scale.”

The system orbits the sun-like star HD 168443, which is 123 light-years from Earth in the constellation Serpens.

The new finding feeds a contentious debate about whether large extrasolar planets are indeed planets, or are brown dwarfs, which are big balls of gas that glow briefly but are not big or hot enough to sustain nuclear fusion and become stars.