Dust Near Stars Said to Be Precursor of Planets : Astronomy: Hubble telescope reveals huge disks of material around young suns. The matter will eventually condense into spheres, scientists say.
The repaired Hubble Space Telescope has given astronomers their clearest look yet at the process of planetary formation around other stars, scientists said last week.
Observing 110 young stars in the Orion Nebula, a great cloud of interstellar gas 1,500 light years from Earth, astronomer C. Robert O’Dell of Rice University in Houston found that more than half were surrounded by mammoth disks of dust that researchers believe will eventually condense into planets.
The discovery is “strong proof” that the so-called protoplanetary disks, and hence planets themselves, are “a common product of star formation,” O’Dell said at a NASA news conference in Washington.
The observations confirm indirect evidence that planets, and thus life itself, are not unique to our own solar system, but are ubiquitous throughout the universe. “This is one more (piece of) the argument” that life exists elsewhere, O’Dell said.
And unlike the recent discovery of three planets circling an unusual star called a pulsar, the new observations involve stars much more similar to our own sun and should lend insight into the genesis of the Earth and its neighbors, O’Dell said.
“We have a lot to learn about the formation of our solar system by watching these (protoplanetary disks),” said astronomer Anne L. Kinney of the Space Telescope Science Institute in Baltimore.
The search for evidence of planets and planetary formation outside our solar system has long been a preoccupation of astronomers, many of whom refuse to believe that humans are alone in the universe. Mathematical formulations indicate that if there are a lot of planets, then the probability of life existing independently of Earth is also high.
That quest has been extremely difficult because planets are so small and dim. Planets the size of those in our solar system could not be seen by the Hubble telescope even if they were circling the nearest star, only four light years away, according to astronomer Suzan Edwards of Smith College in Northampton, Mass.
But if those same planets were ground up into small pieces and scattered through an area the size of our solar system or larger, they would form a cloud that would be a lot easier to spot, said astronomer Stephen P. Maran of NASA’s Goddard Space Flight Center in Greenbelt, Md.
And with its newly repaired optics, in fact, the Hubble did spot such protoplanetary disks in the first place it looked, the stellar nursery called the Orion Nebula. Less than 1 million years old, the nebula is a seething mass of hot gases that are condensing into stars much like our own. The density of matter in the nebula is about 100,000 times the density in the region of our solar system.
Conventional theory suggests that when a clump of gas and dust coalesces under the force of gravity to form a star, from 1% to 10% of the original material is left behind and accumulates in a disk around the star, Edwards said. Eventually, gravity also causes matter in the disks to coalesce into planets.
O’Dell originally observed the disks with the Hubble two years ago, before the telescope was repaired. But the resolution was so poor because of the instrument’s faulty optics that it was impossible to tell whether he was observing disks or shells of dust that were unlikely to coalesce into planets. Now, since the repair, the resolution of the telescope is twice as good, enabling him and his colleagues to see that they are in fact disks.
Furthermore, the increased resolution enabled them to estimate the mass and density of the disks. They found that the mass of the outer edge of the disks, for example, was large enough to make seven to 10 Earths.
O’Dell said that it is virtually certain that he is watching planetary formation. “There is no possible alternative explanation for the observations,” he said. “Once you’ve seen them (the disks), this has got to be what it is.”
