Hubble returns data on planets

Images may offer proof that they form around other stars

Images taken by NASA's Hubble Space Telescope have produced the strongest evidence yet of planetary formation around stars other than the sun, astronomers said Wednesday.

If their theories prove correct, the thick discs of particles and gas spotted by the space telescope that surround 40 percent of a collection of young sunlike stars in the constellation Orion could coalesce into planets within 10 million years.

"What we are seeing here is a missing link in the whole process of the formation of planets," said Robert O'Dell, a Rice University astronomer and the Hubble science team researcher responsible for the discovery.

"Now we have direct evidence that the material necessary for the formation of planets exists around about one half of the stars that are similar to our own sun, thus raising the probability that the existence of planets around other stars is much more certain that we thought before," O'Dell said.

The constellation Orion, which is clearly visible in the December sky over the Southern United States, is about 1,500 light years away, close in terms of the vast distances of the universe.

In making the announcement, O'Dell and his colleagues were careful to stress they were not producing solid evidence of planets around another star.

But they contend their Hubble images surpass the previous best evidence of planetary formation around other stars, obtained by NASA's Infrared Astronomy Satellite.

O'Dell said the discovery of what researchers term "proto planetary disks" was largely an accident and was made as he studied images taken by the Hubble as it was trained on what is known as the Orion Cloud, an area about halfway down the mythical sword that hangs from the bright string of stars that forms Orion's belt.

The area is heated and illuminated by a central bright object, which made a collection of young stars in the same realm visible to the space telescope. By O'Dell's count, about 40 percent of the stars were surrounded by bright disks of dust and gas.

In many instances the disks contained enough material to gradually coalesce into a system of planets similar to the solar system. The disks photographed earlier by NASA's Infrared Astronomy Satellite were too thin to produce planets.

According to University of Massachusetts astronomer Steve Strom, an expert in the field of planet and star formation, each speck of dust in the disks is about the size of a grain of sand.

The disks of dust and gas are spinning too rapidly to join the nascent stars they surround. As the particles collide, they begin to clump into larger and larger objects, gradually forming planetary systems.

"This is probably a very common process. Astronomers firmly believe there are a lot of planets out there," said NASA's Ed Weiler, the Hubble's chief scientist.

A space shuttle crew is scheduled to repair an optical flaw in the telescope next year.

Scientists hope the repairs will provide the kind of optical clarity required to actually observe a large planet around a nearby star.