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Dust Hints at Nearby Solar System

8 July 1998 7:00 pm
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Jewel in the crown? The bright knot at the 8 o'clock position in Epsilon Eridani's dust disk might signal a planet.

A ring of dust, probably kicked up by a swarm of comets, has been spotted around Epsilon Eridani, the nearest sunlike star, just 10 light-years away. "What we see looks just like the [dusty] comet belt on the outskirts of our own solar system," says Jane Greaves of the Joint Astronomy Center in Hawaii, who announced the discovery today at the Protostars and Planets Conference in Santa Barbara, California. The appearance of the dust ring also suggests that planets are orbiting nearby, says Greaves.


Greaves and her colleagues imaged the ring with a sensitive camera that captures the short, "submillimeter" radio waves given off by warm dust, attached to the 15-meter James Clerk Maxwell Telescope at Mauna Kea, Hawaii. The Hawaii team and others had already spotted similar disks around other stars (ScienceNOW, 24 June). But Epsilon Eridani is cooler and more sunlike than any other star known to have a disk, and because it is so close, the dust ring--which can be seen face-on--shows unprecedented detail. The dusty doughnut is about the size of our solar system's Kuiper belt, a flattened disk of comets outside Neptune's orbit. But the strength of the submillimeter waves implies that the dust is far denser than it is in the Kuiper belt. If it really is cometary debris, the number of comets orbiting the star must be 1000 times larger than in the solar system.

The inner region of the disk, comparable in size to our own planetary system, contains little material, perhaps because it has been swept clean by planets forming from the dust. A bright spot in the ring is probably "either dust trapped around a planet, or dust perturbed by a planet orbiting just inside the ring," says Greaves. It is "good evidence but not convincing proof" of a planet, agrees theorist Jack Lissauer of the NASA Ames Research Center in Mountain View, California.

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