Smallest Distant Planets Yet Detected

WASHINGTON, D.C.--The planet hunters are at it again, and this time, they've bagged two Saturn-sized worlds. The two planets orbiting distant stars are the smallest extrasolar planets yet found, and they're the first proof that scientists would be able to spot a solar system with a geometry like our own.

In the past 5 years, astronomers have detected about 30 planets beyond our sun's neighborhood. No one has seen these distant planets directly, but they are revealed by their gravity: The tug of orbiting planets creates telltale wobbles in a star's motion. Smaller planets exert less power over their suns, so it has been all but impossible to find a planet very distant from its sun or smaller than about half the mass of Jupiter--until recently.

Astronomers Geoff Marcy of the University of California, Berkeley, and Paul Butler of the Carnegie Institution of Washington, D.C., have found about two-thirds of all the extrasolar planets to date. Now, they have tripled the precision of their spectrometer and detected two planets roughly one-third the size of Jupiter, they announced today at a NASA press briefing. The first planet orbits the star HD43675, located 109 light-years away in the constellation Monoceros; the second orbits the star 79 Ceti, 117 light-years away in the constellation Cetus. The detection of such small planets means that Marcy and Butler's equipment is sensitive enough to detect a twin of our solar system, one with a Jupiter-mass planet fairly distant from its star.

Carnegie Institution astrophysicist Alan Boss believes that the detection of these two planets suggests that there are a whole range of planetary masses in alien systems--from rare super-Jupiters to fairly common sub-Saturns and below. "What we're seeing is really just the tip of the iceberg," he says. NASA space scientist Anne Kinney concurs: "This is brand new; we're going to learn what kind of animals are in that zoo."

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