Planet hunters

By day, they work in many fields. By night, they help professional astronomers search for faraway worlds.

A suburban backyard nearly an hour's drive north of San Jose, Calif., might seem to be an unlikely spot for taking part in one of modern astronomy's grandest adventures.

Yet when the last faint glow of dusk vanishes from cloudless skies, Ron Bissinger is likely to head to his modest garden-shed observatory to begin his search for worlds beyond our solar system.

A software-company vice president by day, Mr. Bissinger is one of a

handful of amateurs helping to create a potentially worldwide collaboration between amateur and professional astronomers.

Their common cause is the search for planets that eclipse their parent stars. Such backlit planets can reveal characteristics that could lead to the discovery of a world beyond our sun's reach that displays evidence of organic life.

Five years ago, the notion of enlisting amateur astronomers in extrasolar planet exploration probably would have drawn snickers at an astronomy conference. The task would have been deemed too difficult for equipment available to the backyard enthusiast.

But two years ago, a team of amateurs in Finland observed the transit of a planet orbiting a star 150 light-years away in the constellation Pegasus.

Professionals sat up and took notice.

The Finnish group summarized its results in Sky and Telescope magazine in January 2001. After looking at the data, "I realized that the equipment readily available to high-end, interested, committed amateurs is more than capable of discovering these transits," says Greg Laughlin, an astronomer at the University of California at Santa Cruz and a member of a team based at UC-Berkeley credited with discovering more than 50 extrasolar planets.

For amateurs engaged in the search, the quest can be a life-altering experience.

"It's definitely not helping my sleep cycle any," Bissinger quips during a phone interview from his Pleasanton, Calif., home. "I have an 11-year-old daughter who came to me about six months ago and said, 'Dad, I've concluded that you're nocturnal.' "

Yet the prospect of participating with the pros in one of astronomy's cutting-edge fields is too alluring to pass up, he adds. "What drives me is the childlike wonder – the awe I have doing this in the shadow of some very smart, very good people."

The project, known as Transitsearch.org, began to take shape in January, spearheaded by Dr. Laughlin and Tim Castellano of NASA's Ames Research Center in Mountain View, Calif.

It comes at an opportune moment. During the past few years, concerns about the danger to Earth from comets and asteroids have triggered several government and privately funded programs to look for these objects. Some of these efforts are highly automated and take advantage of telescope optics designed for military use, leaving many amateur observers eating comet dust.

At the same time, professional astronomers have been detecting new planets beyond our solar system at an accelerating rate.

Since 1995, astronomers have detected 100 extrasolar planets. That pace is likely to accelerate, researchers say, as technology improves and researchers dedicate more telescope time to the hunt. The Berkeley team, for example, has funding to build a 1-meter-class telescope at the Lick Observatory. It will be employed full-time as a planet hunter.

Out of the first 100 extrasolar planets detected, one is known to transit its home sun. As the list of new planets grows, astronomers anticipate the number of transiting planets will grow.

Once astronomers discover a planet, however, they usually aim their telescopes at the next star on their search list.

Debra Fischer, an astronomer at the University of California at Berkeley and another member of the planet-hunting team, notes that competition for telescope time is intense. Projects to find transiting planets are too time-consuming and scientifically risky to make the cut.

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."

Tools of the trade

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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