Small telescopes doing amazing things. That’s the theme of the day in exoplanet hunting, reinforced by the announcement of a new planet discovered by the Trans-Atlantic Exoplanet Survey (TrES). Small, automated equipment and off-the-shelf camera technology went into this work, which spotted the third transiting planet found with the kind of telescopes available to amateurs. “Hunting for planets with amateur equipment seemed crazy when we started the project,” says David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics, “but with this discovery the approach has become mainstream.”
Image: A computer-generated simulation of TrES-2 crossing (transiting) the disk of its host star. TrES-2 transits farther from the disk center than any other known transiting planet. The transit of TrES-2 causes a drop in the brightness of its home star of about one and a half percent. This slight dimming of the star’s light was noticed and measured by the TrES researchers, who used the parameters of the transit to determine the planet’s mass, size and other properties. Credit: Jeffrey Hall, Lowell Observatory.
Here’s how TrES works: A network of small telescopes are automated to make wide-field exposures on observing runs that typically last about two months. The data, consisting of observations of tens of thousands of stars, are then run through software that examines the light curve of each, looking for the telltale signs of a planetary transit across the star. That’s no small task given the number of false positives that are bound to arise from binary star systems.
But when the data have been combed through and a suitable candidate found, the 10-meter instruments at the Keck Observatory on Mauna Kea (Hawaii) go to work to confirm the discovery. TrES also includes telescopes at the Palomar Observatory, the Planet Search Survey Telescope at Lowell Observatory in Arizona, and the Stellar Astrophysics and Research on Exoplanets (STARE) telescope in the Canary Islands.
Transits are terrifically useful finds because when they occur around nearby stars, they provide uniquely accurate size and mass measurements. The new world, TrES-2, blocks about one and a half percent of the light of its star, some 500 light years away in Draco. It’s larger than Jupiter and passes in front of the primary every two and a half days. Usefully, TrES-2 is also in a part of the sky that the upcoming Kepler mission will examine, allowing astronomers to plan ahead for a thorough examination of the planetary system. Adds Charbonneau, “TrES-2 will likely become the best-studied planet outside the Solar system once Kepler flies.”
This work has been submitted to the Astrophysical Journal Letters, and though I don’t yet see a link to it at arXiv, you can download a PDF of O’Donovan et al., “TrES–2: The First Transiting Planet in the Kepler Field” here. Also helpful by way of background is Charbonneau et al., “When Extrasolar Planets Transit Their Parent Stars,” available online.