Planet Search Getting Easier
H O N O L U L U, Jan. 29, 2001 -- For millennia, man-kind has pondered and searched for worlds outside oursolar system — for planets like Earth that could support life.
But since the advent of modern astronomy centuries ago, detection of distant planets has proved to be as difficult as finding grains of sugar on a beach. Stars, billions of times more brilliant than the worlds that circle them, make planets all but impossible to find. And decades of intense observation yielded only false alarms, earning planet-hunting a reputation as a backwater of astronomy.
During the past three years, however, this perception has radicallychanged. Through advances in technology, an improved understanding ofplanetary behavior, and increased access to better telescopes, astronomershave found 17 planets since 1995. These discoveries have revolutionizedplanetary science, forcing scientists to revise long-held theories aboutthe universe and making planet-searching one of the hottest fields ofastronomy.
More Light Caught By Bigger Eyes
“The major change has been access to large telescopes like the Keck [atelescope in Hawaii with a mirror 30 feet across],” says William Cochran,an astronomer at the University of Texas at Austin. “With big scopes, youget a lot more light. And the faster you can get light, the faster you candetect these planets.”
In many ways, the recent discovery of what could be a nascent solar system220 light-years from Earth is a symbol of this planet-hunting renaissance.Images of the would-be solar system were first captured by the Kecktelescope. Later, using the Hubble Space Telescope, University of Hawaiiastronomer Bradford Smith discovered that there might be a planet withinthe new solar system. He found the planet by searching the heavens in adifferent way — by looking at disks of dust around stars.
Image Sifting Finds Ringed Object
He sifted infrared images of the star 220 light years away, dubbed HR4796A.
Inside its disk sat a ring that looked like hula hoop. “When wepulled the image of this star ring up on the computer screen, it lookedlike Saturn,“ says Dr. Smith. “It was like, ‘Wow!’ We had not reallyexpected that.“
The same image that floored Smith brought a room full of normally sedateastronomers to their feet for a standing ovation at the AmericanAstronomical Society meeting earlier this month.
Indeed, the find is a breakthrough. According to previous theories, noplanetary candidate should be there. The star is only 8 million to 10million years old, supposedly far too young to have developed a large,far-flung planet like the one indicated in the Hubble images.
But that’s really no great surprise. Beyond the quixotic object found bySmith in the gloaming of deep space, astronomers are finding other planetsthat do not conform to traditional models.
Newer Planets Break All the Rules
For one thing, many are massive — as large as Jupiter but with short orbitscloser to their host stars than Mercury is to the sun. Theoretically,Jupiter-like planets were supposed to be found orbiting farther away fromtheir host stars, where they would not be sucked in by the stellar bodies’strong gravitational pull.
Many of the newly discovered planets were also found to have ellipticalorbits — unlike those of planets in our solar system, which are largelycircular.
Theorists are now scrambling to rebuild planetary theory based on theseobservations. They have already come up with some explanations. “HotJupiters” might be migrating toward their host stars, destroying otherplanets that lay in their paths, scientists say. Meanwhile, the ellipticalorbits of extrasolar planets might be caused by the gravitational pull ofeither a nearby star or planet.
New Methods of Searching
In addition to learning more about planets themselves, scientists havelearned more about how to look for them. Before the binge in planetarydiscovery, money to finance planet searches was hard to come by. “For along time, whenever anyone asked for money to find planets, everybodylaughed and threw their proposal away,” says William Borucki, a researcherat the NASA/Ames Research Center in California.
Then in October 1995, two astronomers in Switzerland noticed that the lightspectrum of the star 51 Pegasi was wobbling. Upon closer examination, thescientists concluded that the phenomenon was caused by a large planetorbiting very close to the star. After that, the wobble — previously only atheory — became a telltale sign for planet hunters and helped resuscitatethe field.
In fact, new research shows that 5 percent of the stars surveyed showevidence of planets.
We May Still Be an Anomaly
Still, astronomers are far from a consensus that an Earth-like body exists.“It is still being argued today by many people that our own solar system isan absolute anomaly,” says Smith. “On the other side of it, there are manypeople who believe that when you form stars you form planets at the sametime.”
In the next decade, a new generation of highly sensitive telescopes willturn their mirrors heavenward. Most will dedicate sky time to planetsearches. Scientists are also perfecting new techniques that useless-expensive equipment to locate planets. And direct imaging of distantstars with infrared instruments promises to produce more snapshots of starsand planets, too.
But all these new high-powered tools still can only give scientistsevidence that planets exist — they cannot give a direct picture of anEarth-like planet. “The problem is Earth-like planets are small andwhatever effect they have is going to be much more difficult to detect,”says Smith.