Tiny scope spies distant planet.

Using a telescope not much bigger than the one Galileo invented nearly 400 years ago, astronomers have discovered a planet orbiting a star 500 light-years from Earth. The 4-inch telescope in the Canary Islands is one of three small, globally separated telescopes that monitor the brightness of some 12,000 stars in the constellation Lyra. Periodic dips in brightness can result from an orbiting planet crossing in front of a star.

Searching for such planetary transits with the Canary Islands telescope, Roi Alonso of the Astrophysical Institute of the Canary Islands found evidence of a Jupiter-size planet whipping around a sunlike star every 3.03 days.

"The discovery demonstrates that even humble telescopes can make huge contributions to planet searches," says discovery team member Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. The two other telescopes in the Trans-Atlantic Exoplanet Survey (TrES) network reside at Palomar Observatory near Escondido, Calif., and at Lowell Observatory in Flagstaff, Ariz.

Alonso, Torres, and their coworkers relied on much larger telescopes to verify the transit and to obtain a spectrum of the affected star. The spectrum clinches the finding because it reveals that the star wobbles back and forth in response to the gravity of an unseen planet, the researchers report in an upcoming Astrophysical Journal Letters.--R.C.