Solar system replica?

Looking at a star 90 light-years away, astronomers have found what may be the closest analog known to our solar system. By recording the motion of the sunlike star HD 70642 for 5 years, scientists have discerned that an unseen planet at least twice as massive as Jupiter is tugging on it.

Like Jupiter, this extrasolar planet lies billions of miles from its parent star. It shares another important property with Jupiter: Its orbit is nearly circular, a rarity among planets that lie relatively far from their parent stars. Simulations show that outer planets with such a trajectory are conducive to the survival of inner planets that could harbor life.

In contrast, massive outer planets with elongated orbits act like gravitational slingshots that are likely to eject an inner planet that's on an Earthlike path, notes Hugh R.A. Jones of the Liverpool John Moores University in England. An inner planet that did manage to stay in orbit would have its path elongated by the interaction, subjecting the body to huge temperature swings. Such variations would make it much less likely that life could survive.

Jones and his colleagues report their findings in the Aug. 10 Astrophysical Journal Letters.

John E. Chambers of NASA's Ames Research Center in Moffett Field, Calif., cautions that if the newfound planet is either much heavier than its known minimum mass or if the star is host to another massive planet, an inner Earthlike planet could still be ejected from the system. Nonetheless, this system is "one of the best places to look [for an Earthlike body] among the planetary systems we know of," he says.--R. C.