WHEN is a large planet not a large planet? When it鈥檚 two smaller ones in disguise, a possibility that suggests we may have found a world the size of Earth without realising.
Guillem Anglada-Escud茅 of the University of Barcelona, Spain, and colleagues re-examined why certain stars wobble. This back-and-forth motion is often attributed to the gravitational pull of a large planet in a close, eccentric orbit. However, their mathematical models suggest the wobble of some stars could instead be the signature of a pair of smaller planets on circular paths, one orbiting exactly twice as fast as the other.
Gliese 876 is the only star known to have such a pair in this kind of orbit. But Anglada-Escud茅 estimates that as many as half of the 300 known planets outside our solar system may have been misidentified, and that half a dozen systems could contain inner planets the size of Earth ().
Advertisement
Distinguishing the subtle differences in the star wobble data will require precise measurements collected over months or years, says Francesco Pepe at the University of Geneva, Switzerland.
