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Appalachian Astronomers Search for “Trojan” Planets

By William Purcell

BOONE — Of the billions upon billions of stars in the night sky, four keep Dan Caton up at night.

The Appalachian State University astronomer leads a team of graduate and undergraduate researchers who focus Appalachian’s Dark Sky Observatory telescopes on two sets of stars that Caton believes could harbor a planet.

In addition to being among very few astronomers in the world winning grant money to search for new planets, Caton is the only astronomer looking for “Trojan” planets, a phrase

Caton uses to describe his new theory of where planets can exist. He hopes to join a small circle

of astronomers who have discovered 28 planets outside of the Earth’s solar system.

“The existence of planets is interesting,” Caton admits. “However, much more interesting is if there is life on those planets. But, you have to find the planet first.”

Promising data from a pilot study conducted at Dark Sky Observatory last summer helped Caton win funding from the National Science Foundation (NSF) to extend his quest through 2002. The NSF grant allows Caton to continue researching if the two star systems have a planet and to continue searching other binary star systems, too.

“Finding a planet is all about where to look,” Caton said. “And we’re looking where no other astronomers are looking. We’re looking where no one thought a planet could exist, until now.”

Caton’s search for a planet began in an introductory astronomy course three years ago. While teaching mostly freshman and sophomore students about two groups of asteroids orbiting the sun near Jupiter, the proverbial lightbulb went off above Caton’s head.

“I explained how a group of asteroids were held in orbit at the tip of a triangle with Jupiter and the sun forming the base of the triangle,” Caton said. “It hit me out of the blue.

“If asteroids can hold a steady orbit around our sun while in lockstep with Jupiter, why couldn’t a planet do the same thing with two stars?”

Unlike the sun, the vast majority of stars come in orbiting pairs called binary stars. In many of those star pairs, one star is much larger than the other, just like the sun is much larger than Jupiter. Caton theorizes that a planet could orbit in a binary star system in the same way that asteroids orbit in relation to the sun and Jupiter. Dubbed Trojan planets after Jupiter’s Trojan asteroids, the name of Caton’s theory refers to the Greek myth of soldiers hiding inside a wooden horse. A Trojan planet hides inside the orbit of the smaller star.

“The search for planets is a bit like the search for life–you want to look in all possible places,” Caton said.

Caton and his team use two telescopes at Dark Sky Observatory for the search. Digital cameras take images of the binary stars and computers detect subtle changes in the light of the stars. The change in light signals to astronomers that a planet is orbiting the star.

Last June, Caton’s team detected changes in light in two different star systems suggesting the possibility of planets there. However, the team can’t look at the systems again until the summer of 2001 when the stars become visible again in Northwest North Carolina. In the meantime, the team is focusing on 20 other binary star systems.

Weather permitting, the team works in shifts all night taking more than 500 images. The images are copied onto compact discs and later processed by computers to determine if a planet has been detected.

Dark Sky Observatory is located on a remote 120-acre tract 20 miles from campus in Ashe County. Its telescopes are used every hour of every night with time divided equally between Caton’s search for “Trojan” planets, Dr. Richard Gray’s NASA study of stars most likely to harbor a planet with life and Dr. Joseph Pollock’s study of quasars.

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