Planet hunters

Among the uncertainties: While techniques for discovering planets can establish a planet's presence, they can't determine if astronomers are seeing a planetary system edge-on – a view that reveals the subtle dimming of a star as a planet crossed its face.

Yet of the extrasolar planets discovered, "statistically there's another planet in there that's transiting," she says. "We just haven't found it yet."

Enter the amateurs. Armed with Laughlin's projections of when and how long a planetary transit could be expected to occur, they would monitor the parent star, looking for evidence of the telltale dimming.

Finding another transiting planet "would be a huge scientific bonanza," Laughlin says.

He cites a star with the prosaic name HD209458 as an example. In 1999, astronomers reported evidence of a giant gas planet orbiting the star. Observations revealed the star dimmed slightly as the planet swung between it and earthbound observers.

Within a year, astronomers began looking for signatures of the planet's atmosphere. Last year, a team led by CalTech astronomer David Charbonneau reported observing sodium in the planet's atmosphere. The team also has been looking for signatures of other gases, such as methane, water vapor, potassium, and other elements.

"This opens up an exciting new phase of extrasolar planet exploration, where we can begin to compare and contrast the atmospheres of planets around other stars," Dr. Charbonneau notes. HD209458 also was the star the Finnish team used to demonstrate that planetary transits beyond our solar system are within reach of amateur-class equipment.

Extrasolar planet hunting can seem a daunting activity. Laughlin estimates the equipment – telescope, a specialized digital camera, computer, and software – could top $5,000. It might take up to six months to get the hang of observing techniques.

But Bissinger says many amateurs already have the necessary equipment. He took up astronomy about seven years ago and bought his digital imager to take pictures of the objects he was observing.

He, too, was captivated by the Finnish team's work. After working with Castellano and Laughlin, he says it took him two nights to get his equipment configured properly. He spotted HD209458's companion in transit the second night.

The dimming of the star "pops right out of the data. It was a real Eureka moment for me," he says. "That transit occurred 150 years ago, during the Civil War."

To him, the blending of amateurs and professionals in exploring new solar systems is a natural. And in an era of tight budgets, the price is right.

"We've got time on our hands," he says. "And we can watch for nothing."

For amateur astronomers interested in joining the search for planets orbiting other stars, the list of tools is short. Greg Laughlin, an astronomer at the University of California at Santa Cruz, estimates that a planet-hunting system could be built from scratch for around $5,000.

What you'll need:

• A telescope, whose primary light-gathering lens or mirror ranges from 4 to 12 inches. The telescope should be able to track stars across the sky through computer controls or a built-in star-tracking system.

• A CCD imager that mounts at the rear of the telescope.

• A laptop computer. The team also recommends several computer programs to handle tasks ranging from processing the images to spreadsheet programs to analyze the information from those images.

Detailed examples of telescopes, imagers, and computer requirements can be found at www.transitsearch.org/obsproc.htm.

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