Catching Stellar Views ; 'Adaptive Optics' Lets Scientists Reduce the Light Cast by Stars and See Hidden Planets

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To anyone whose childhood echoed with the tune of "Twinkle, Twinkle, Little Star," the idea of taking the twinkle out of starlight might verge on the unromantic, if not the heretical.

Remove the twinkle, however, and you may find that two little stars actually are four, and one appears to host a nursery for planets. Look even closer, and you may find that the blurring twinkle masks the presence of a planet.

The technology to remove the twinkle has come of age, researchers say. Known as adaptive optics, the approach holds the promise of allowing astronomers using large ground-based telescopes to make digital images of an extrasolar planet long before space-based telescopes are launched to do the same task.

The ultimate goal is to use both sets of tools to gain a clearer understanding of the conditions that give rise to solar systems, the systems' intriguing diversity, and, perhaps, the presence of life elsewhere in the galaxy.

"Within the next five to 10 years, we should be able to answer the question" of whether

other solar systems like ours dot the sun's neighborhood," says Alan Boss, a astrophysicist at the Carnegie Institution of Washington. "The more planets we detect, the more we see that other solar systems have characteristics like our own. We're not a fluke."

Over the past decade, astronomers have discovered 78 planets orbiting other stars. The planets range in mass from 24 percent Jupiter's mass to nearly 17 times the Jovian planet's heft.

The newest member of the list was announced Jan. 8 during the winter meeting of the American Astronomical Society (AAS). A team led by Sabine Frink of the University of California at San Diego reported the discovery of a planet around the star Iota Dracona, in the constellation Draco.

The find is unique, the researchers say, because the host star has used up most of its hydrogen fuel and has expanded to a radius 13 times as large as the sun's.

"Until now, it was not known if planets existed around giant stars," notes Dr. Frink. "This provides the first evidence that planets at earthlike distances can survive the evolution of their host star into a giant."

Yet, researchers say, none of the planets discovered so far have been directly imaged using adaptive optics.

The problem is that a host star far outshines any planet it anchors, notes Ray Jayawardhana, an astronomer at the University of California at Berkeley. "Viewed from far outside the solar system, Jupiter would be one billion times fainter than the sun in the infrared," he says.

Thus, astronomers have had to content themselves with inferring a planet's presence by its influence on its host star.

The first generally accepted detection of an extrasolar planet was reported 10 years ago, when a pair of radio astronomers claimed to have found a pair of planets orbiting a pulsar. They detected the planets by their effect on the arrival time of radio signals from the rapidly spinning remnant of a supernova. The vast majority of extrasolar planets have been detected by the tug they exert on their parent star. If the star is close enough, in principle the tug can be detected visually by the star's wobble against stars that are so far away they appear fixed in the sky.

So far, however, this method has failed to yield a confirmed sighting of a new planet. Thus, astronomers must look for changes in a star's spectrum, which appears to alternately stretch and compress as a planet orbits in the line of sight of an observer on Earth, pushing and pulling on the star.

In some cases, a planet can be detected by the effect it has on a star's light as it passes between the star and the astronomer's telescope. Last November, astronomers announced that they had used a variation of this technique to detect an extrasolar planet's atmosphere.

A team led by David Charbonneau of the California Institute of Technology used the Hubble Space Telescope to track a planet's orbit around HD 209458, a sun-like star some 150 light-years from Earth in the constellation Pegasus. …