It has been XX centuries since an amateur made a significant contribution to planet huntingWith the tally of planets around other stars hovering around 100 and growing rapidly, amateurs are being invited to join the search for other worlds in an effort to confirm detections of presumed planets and improve understanding of their sizes and other characteristics.
A new Web-based initiative could mark the re-entry of amateurs into the ranks of planet hunters -- a heady group that has long exhibited the resourcefulness unique to backyard stargazers. In 1781, William Herschel found Uranus using an amateur telescope at home. Clyde Tombaugh found Pluto in 1930 at the age of 23 after his amateur efforts got him a real job as a professional astronomer.
For the next 65 years, no new planets were found.
Then in 1995, the first planet outside our solar system was detected by a painstaking process -- once considered improbable by mainstream astronomers -- that involves watching for the wobble of a star induced by the gravity of a planet. Now about 100 of these so-called extrasolar planets have been detected. Importantly, however, this wobble method is considered indirect, and the presence of these planets yearns for confirmation by direct means.
In 1999, for the first and only time, one of these other worlds was confirmed to exist by a direct observational method, in which a dip in starlight was noted when the planet passed in front of its host star.
Astronomers have since realized that these transits could be spotted with 8-inch telescopes, a type common among serious backyard skywatchers and only slightly smaller than the one Clyde Tombaugh used to discover Pluto. The telescopes must be equipped with modern electronic cameras, also common among devoted amateurs.
But no transit will be as easy to spot as the one in 1999, which involved a huge planet orbiting extremely close to a relatively nearby star called HD 209458.
Even for this huge planet the change in brightness is only about 1 percent. Although this is too small for the eye to discern, recent progress in the price and quality of electronic imaging cameras and computer controlled telescopes for amateurs make the project feasible, explains Tim Castellano of NASA's Ames Research Center.
So-called CCD (charge coupled device) cameras have been used by professional astronomers for decades, on Earth and in space. The Hubble Space Telescope uses one.
Online clearinghouse
Castellano said the transit of HD 209458 made it obvious that amateur CCD cameras mounted on an 8-inch or 10-inch telescope could make such subtle observations. Further, he and Gregory Laughlin, of the University of California, Santa Cruz, think looking for planet transits its a perfect job for amateur astronomers, who can point their telescopes wherever they want whenever they want.
Laughlin expects people will volunteer their time for the chance to be involved in important discoveries.
The researchers have set up an online clearinghouse for information on extrasolar planets and hope well-equipped backyard stargazers will be interested in attempting the long-odds observations that could yield only the second direct detection of another world.
In a recent interview, Laughlin explained why the project is needed.
Only a small percentage of extrasolar planets can be expected to transit their stars as seen from our view. The farther a planet is from the star, the lower the odds are that a transit will occur.
The indirect wobble-detection method (officially called the radial velocity technique) cannot predict if a planet will transit a star or not. Nor can it firmly determine the mass of a planet (it sets an upper limit) or yield a well defined orbit.
Once a planet is observed to transit star, however, its exact mass and diameter can be determined and its orbit precisely pinned down. In some cases, powerful observatories like the Hubble Space Telescope can then be used to probe the planet's atmosphere, as was done for the first time late last year, with HD 209458. All this information tells astronomers to what extent other planets and solar systems are like our own, and therefore how likely it is that they might harbor habitable planets like Earth.
"The value added by a transit detection is enormous," said Laughlin, who also works at the Lick Observatory, where he assists the world's most prolific planet hunters, a team led by Geoffrey Marcy of the University of California, Berkeley and Paul Butler of the Carnegie Institution of Washington.
Long odds, high reward
The odds of success for any volunteers will be inherently slim.
Planets that orbit very close to their stars -- making the trip in less than a week -- have roughly a 10 percent chance of being aligned in such a way that they will transit their star as seen from Earth. "And those are chased down immediately" by professionals, Laughlin said. But further from the star, the chances of a transit go down and the prediction for when the transit is going to occur gets murkier and murkier.
"You're chasing down ever lower probabilities over ever longer windows," Laughlin said. And securing time on large telescopes is a competitive process, one sometimes not keen on low odds for payoff.
"There are a lot of very dedicated amateurs who are willing to spend time on projects that might have a lower probability of paying off," Laughlin said. "They're not constrained by having to write a paper or get grant funding for this year. But make no mistake: This will be very time consuming and difficult work."
The program could be effective with just a few observers, but a few dozen participants would mean more stars could be surveyed. Importantly, having observers in various locations around the world would provide the necessary 24-hour coverage of a star to generate the best results.
Castellano said the project's search technique is easy to understand.
"We use a small telescope and take a night-long series of electronic pictures of a star we are interested in, and some nearby ones for comparison purposes, and look for the small changes in brightness characteristic of the transit of a planet," he said.
Discoveries should be possible for persistent and skilled skywatchers with modest telescopes. "At least three amateur astronomers I am aware of have successfully observed the transit of HD 209458 in suburban backyards," Castellano said.
The web site, www.transitsearch.org, will provide information on select stars, a forum for discussion and a form for submitting results, which would be reviewed by Laughlin and Castellano.
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