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Possible Far-Distant Planetary System Comes to Light

ASTRONOMERS who spend their time peering through the cosmos may have found evidence of a new planetary system - a mere 52 light-years away.

Puzzling glitches in the light that travels from one of their prime suspects - a star named Beta Pictoris - may be caused by comets moving under the gravitational pull of planets.

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Using a computer model of our own solar system as an example, Harold F. Levison and colleagues at the Southwest Research Institute in San Antonio show how such a system of planets and comets could account for the phenomena seen in the vicinity of the star. Explaining his research, which was published today in the journal Nature, Dr. Levison acknowledged that for scientists, it will strengthen the case for a planetary system.

Beta Pictoris, found in the southern constellation Pictor, is 13 times more distant than the closest star to Earth, which is four light-years away. A disk surrounding the star shines brightly at infrared (heat radiation) wavelengths. Astronomers think this disk probably contains particles ranging in size from microscopic dust to boulders and even asteroids, to judge from the debris left over from formation of our own solar system. It's the kind of stuff in which a planetary system might well form.

Looking from Earth, we see the disk edge-on. It extends 1,000 astronomical units from the star. An astronomical unit (AU) is the average radius of Earth's orbit - about 93 million miles. Last June, Pierre-Olivier Lagage and Eric Pantin in the French Astrophysical Service in Gif-sur-Yvette, France, published infrared observations of the disk in Nature showing a relatively clear inner area extending out to 15 AU from the star. Planet hunter Charles M. Telesco at the National Aeronautics and Space Administration's Marshall Space Flight Center in Huntsville, Ala., noted in an accompanying commentary that this is what you would expect if one or more planets were sweeping through the region.

Asked about Levison's work, Dr. Telesco said that, although he hasn't yet seen the paper, it will be ``a really interesting step forward'' if it holds up. He added, ``Whenever you can put a body of evidence into a coherent picture like that, everybody feels much better.''

Astronomers have studied Beta Pictoris's glitches for several years. They were puzzled because, if comets were causing the glitches, 90 percent of them would be headed toward the star. Assuming there were no planets, they expected comets to go every which way. Levison now has shown that gravitational interaction between comets and one or more large planets would align the comets so that most would appear to head for the star.

Astronomers have identified more than a hundred stars with surrounding disks. Dr. Telesco noted that looking for planets in them now is a top astronomical priority. He added that the technology is at hand to actually find planets. ``I wouldn't be surprised to see a paper tomorrow'' reporting one has been found, he said.

For example, a planned upgrade of an infrared telescope on Mt. Mauna Kea in Hawaii should enable it to see a planet that's 100,000 times fainter than its parent star. That's the theoretical limit for this particular instrument and a little better than the Hubble Space Telescope can do.

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Dr. David Latham at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who heads a planet search team, says the Mauna Kea instrument already could detect a planet 10,000 times fainter than its star. No alien planet has shown up. The upgraded equipment will be better able to find one.

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