The planetary freak show is getting so crowded it's hard to call them freaks anymore. An analysis of three new Jupiter-sized planets in tight orbits around their suns, presented in the current issue of The Astrophysical Journal, suggests that huge planets with orbits smaller than Mercury's are not oddities--in fact, they may be common.
Last fall, Swiss scientists discovered a planet larger than Saturn locked in a tight orbit around the star 51 Pegasi, upsetting the conventional wisdom about planet formation. "We were fairly seriously humbled," says Geoffrey Marcy, an astronomer at San Francisco State University. "We expected [other solar systems] to resemble the nine planets in our own solar system." Finding such a heifer so near a star was a shock.
After that find, however, Marcy, Paul Butler, and several San Francisco State colleagues retreated to the Lick Observatory in California to scrutinize more than 100 star systems. They found three more 51 Pegasi-class planets, bringing to eight the number of confirmed planetary objects discovered so far outside our solar system. One, almost four times the size of Jupiter, completes an orbit around its star in less than 4 days--lightning fast compared to our 365-day year. Marcy and others suggest that these planets formed further from their suns and spiraled into a closer orbit.
Other experts are skeptical. Some of the purported planets may be brown dwarfs, which are stars that never ignited, says Anita Cochran, an astronomer at the University of Texas, Austin. "I'm still an agnostic about that," she says. "Some might be brown dwarfs, and some look classically like planets."
Marcy and Butler, however, are convinced that these are indeed planets. And they're about to embark on a new odyssey--a 10-year, 400-star planetary search using the Keck telescope in Hawaii. Marcy is betting he'll find more freaks. "The zoo of planetary beasts has a greater set of species than we ever imagined," he says.