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
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. …