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'Hot spots' predict breast cancer's return.

Turning the Hubble Space Telescope toward the Orion Nebula, astronomers have discovered and photographed 15 infant stars surrounded by dense, flattened disks of dust. These images provide the strongest evidence to date, they say, that many young stars develop the dust rings required for planet formation.

The presence of such a large number of protoplanetary disks in the Orion Nebula - a typical gaseous, star-forming region in the constellation Orion- suggests that many suns besides our own possess the ability to evolve planets, according to C. Robert O'Dell of Rice University in Houston, who led the imaging project.

"The disks are a missing link in our understanding of how planets like those in our solar system form:' O'Dell maintains. "Their discovery establishes that the basic material of planets exists around a large fraction of stars."

Current theory on planet formation supported largely by indirect measurements of light reflected or emitted from suspected protoplanetary disks - holds that under certain conditions stars develop dense, revolving dust disks as they hatch in stellar nurseries such as the Orion Nebula.

Scientists have also detected traces of protoplanetary disks in a nebulous region that stretches across the constellations Taurus and Auriga. The dust in such disks emits infrared energy and induces telltale, measurable changes in the light of their central stars (SN: 10/3/92, p. 213).

Researchers do not know how often or under what conditions planets evolve from these dusty disks, says Robert A. Brown, an astronomer at the Space Telescope Science Institute in Baltimore. However, the new Hubble images provide direct photographic evidence that "exactly the type of structure we believe produces planets is, in fact, prevalent around many young stars," he adds.

Previously photographed disks, such as one around the star Beta Pictoris, are much thinner and older than the fresh, young objects in the Orion Nebula. These elderly disks, says O'Dell, may be "planetary systems that have failed, because they're so thin you can see through them." Dense disks like those in Orion would stand the best chance of spawning planets, he says.

Indeed, notes O'Dell, some Orion disks are so thick that they completely block out the nebulas intrinsic background radiation, which comes from young, hot stars forming in the cloud. Hubble's camera therefore sees these disks in silhouette. Other disks in the cluster give off their own light because ultraviolet radiation from nearby stars sets their edges aglow.

Brown, a former chief scientist in the Hubble Space Telescope program, says the new observations substantiate past promises by Hubble's supporters that the telescope would prove useful in the search for other solar systems.

Establishing the existence of new solar systems "is one of the most important problems in astronomy," says Brown. "It's very exciting to see the telescope producing valuable evidence like this."
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Title Annotation:number of capillaries in tumor linked with risk of spread
Author:Fackelmann, Kathy A.
Publication:Science News
Date:Dec 19, 1992
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