Hubble Space Telescope pictures made public yesterday have, for the first time, clearly revealed the stellar nurseries in which swirling clouds of sand-sized grains slowly clump together to form new planets.
The stunning pictures, which show that at least 40 percent of the stars studied seem to be undergoing planet birth, give strong confirmation to astronomers' prevailing theories about how stars and planets form.
They also bolster astronomers' belief that planets are commonplace in space, and that therefore life, and even intelligent life, may also be common.
The pictures, in effect, allow us to "look back in time and actually see what our solar system looked like a few million years after the sun formed," said Stephen E. Strom, an astronomer at the University of Massachusetts at Amherst who specializes in star formation. "That's an amazing look back."
The pictures were taken by a team headed by Robert O'Dell of Rice University, one of the pioneers who helped design and plan the Hubble telescope.
At a news conference yesterday at the National Aeronautics and Space Administration headquarters, Dr. Strom said that with the new pictures, Dr. O'Dell "is holding a piece of history in his hands."
The nascent planetary systems are framed against the flowing veil-like reds and blues of the Orion nebula, a huge cloud of interstellar gas 1,500 light years -- or 9 million billion miles -- from Earth that resembles a filmy curtain undulating in a light breeze.
Within that cloudy formation, the pictures show flat disks of dust swirling around 15 stars.
Such disks, according to prevailing theory, are the stuff from which stars, and later a retinue of planets, moons and comets,, are born.
The theory holds that such disks, swirling like a whirlpool, gradually collapse under the relentless pull of gravity, and when the dust and gas are compressed enough, the gravitational pressure causes atoms to fuse, igniting the cloud and creating a new star.
Then, the remaining material still swirling around gradually forms clumps, as specks the size of grains of sand collide and stick together.
Over a few million years, most of the grains collect into chunks almost a mile across. In a few million more, these chunks have collided and stuck together to form planets and moons.
"We are not saying Hubble has discovered planets," explained Hubble program scientist Edward Weiler, "but we have found a place where, in the next few million years, there will be planets."
These newly discovered disks, he said, could not be seen without the great power of the space telescope -- even in its flawed state -- to reveal fine detail.
They represent "a new kind of object" never before seen by astronomers, he said.
"This is taking us further toward the final proof that there may be planets around other stars," Dr. Weiler said, and thus improves the odds of finding life out there.
Dr. O'Dell, who collaborated with Jeff Hester, an astronomer at Arizona State University, and graduate students Zheng Wen and Xi-Hai Hu, said, "What we're seeing here is a missing link in the whole process of forming planets. Now we have direct evidence that the material needed to form planets exists around about half of stars like our own sun. It shows planets are probably common."
The Hubble telescope is to be refurbished with lenses to correct its flawed vision and a new, improved camera during a space shuttle mission scheduled for next December.
Dr. O'Dell is already making plans for the new pictures of this and other planetary birthplaces.