Third rocks from their suns?
Looks as if science is on track to vindicate science fiction--specifically the notion that there are other Earth-like planets spinning around out there. We've known for years of planets orbiting other stars, but they're all huge, gassy heavyweights resembling Jupiter. Now astronomers report discovery of three far-off worlds much closer to our own in size and, they suspect, made more of rock than gas.
Not that they are midgets. Two were described by an American team last week as "Neptunes" because they are more than 17 times the mass of our own world. The smaller of the two was detected in a system called 55 Cancri, whose star, 41 light-years away, was already known to have three larger planets. And a European team a week earlier reported a "super-Earth" about 14 times the size of Earth and largely composed of rock.
The finds open "a new era in exoplanet research, leading to Earth-like planets," says longtime planet hunter Geoffrey Marcy of the University of California-Berkeley, co-discoverer of one of the new worlds. He firmly believes other Earths are out there but cautions not to expect proof right away. Current methods that infer planets from their gravitational tugs on their parent stars are insensitive to anything below about 10 Earth masses. Other methods could reveal hints of Earth-mass objects in the next few years. But the really exciting information on their composition, chemistry, and other clues to their chances for supporting life may take powerful, space-based instruments 15 years or more to get. -Charles W. Petit
This story appears in the September 13, 2004 print edition of U.S. News & World Report.
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