Periodic Dimming Of Bright Starlight Reveals Distant Planet

Using a network of small telescopes and the “transit method” of detection, scientists have made their first direct discovery of a planet orbiting a bright star. A periodic dimming of light from a bright star 500 light-years away revealed the planet’s presence. The star’s intense light will allow scientists to explore the chemical makeup of the planet’s atmosphere in future observations. A paper on the recent discovery will appear on-line today in The Astrophysical Journal Letters.

“This effort further develops the ’transit method’ and lays the groundwork for more research into the composition of the atmospheres surrounding planets outside our solar system,” said Cliff Jacobs, program director in NSF’s division of atmospheric sciences, which funded the discovery. The research is co-funded by NASA. “In this age of mega-astronomical observing tools, it’s amazing that this discovery resulted from modest observing instruments.”

This is the first extrasolar planet discovery made by a dedicated survey of thousands of relatively bright stars in large regions of the sky. It is also the first using the Trans-Atlantic Exoplanet Survey (TrES, pronounced “trace”), a network of small, relatively inexpensive telescopes designed to look specifically for planets orbiting bright stars. The telescopes make use of the transit technique, in which scientists analyze the shadow cast by a planet as it passes between its star and Earth.

The discovery team includes scientists from the Astrophysical Institute of the Canaries (IAC), National Center for Atmospheric Research (NCAR), Harvard-Smithsonian Center for Astrophysics (CfA), Lowell Observatory, and California Institute of Technology.

A team of scientists led by Timothy Brown (NCAR), David Charbonneau (CfA) and Edward Dunham (Lowell Observatory) developed the TrES network. Brown built the optical system of the telescope used in the discovery and located on Tenerife in the Canary Islands. Roi Alonso Sobrino of the IAC discovered the planet, called TrES-1, after three years of persistent planet hunting.

“The fact that we can learn anything at all about a planet 500 light-years away is astonishing,” says Brown. “It’s almost paradoxical that, with the transit method, small telescopes are more efficient than the largest ones, in a time when astronomers are planning 100-meter telescopes,” says Alonso.

Of the approximately 12,000 stars examined by the TrES survey, Alonso identified 16 possible candidates for planet transits. “The TrES survey gave us our initial lineup of suspects. Then, we made follow-up observations to eliminate the imposters,” says co-author Alessandro Sozzetti (CfA/University of Pittsburgh).

Within two months, the team had zeroed in on the most promising candidate. Observations by Torres and Sozzetti using the 10-meter-diameter Keck I telescope in Hawaii clinched the case. “Without this follow-up work the photometric [brightness] surveys can’t tell which of their candidates are actually planets. The proof in the pudding is a spectroscopic orbit [using the Doppler method] for the parent star. That’s why the Keck observations of this star were so important in proving that we had found a true planetary system,” says co-author David Latham (CfA).

Only now has the transit method resulted in a discovery involving a Jupiter-size planet circling a bright star. The success of the transit method opens the possibility of directly determining key information about the planet, such as its mass and radius (size), and its atmospheric components.