New planets can form in under 1,000 years

Nov. 28, 2002 at 2:45 PM
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SEATTLE, Nov. 28 (UPI) -- Instead of planets taking millions of years to form as previously thought, researchers said Thursday new calculations suggest they sometimes can form within a few centuries.

"The first one in our model pops up around 150 years," researcher Thomas Quinn, an astrophysicist at the University of Washington in Seattle, told United Press International. "Things can happen quickly."

When it comes to planetary formation, the standard theory says it takes a million years or more for the solid cores of gas giants such as Jupiter or Saturn to clump from the cosmic debris that whirls around young stars. After the cores appear, according to the theory, it takes another 1 million to 10 million years for envelopes of gas to enshroud them.

Recent surveys of some 1,000 stars reveal about 10 percent have gas giants orbiting them, generally ranging in size from about the mass of Jupiter to 10 times that large. "If they take millions of years to form, then they probably would be a very rare phenomenon," Quinn said.

The new model from Quinn and colleagues suggests the spinning disks of gas that orbit stars break apart after only a few spins. Fragments then quickly begin to coalesce due to gravity. "If this really happens out there, then it would probably dominate the way planets form," Quinn told UPI.

Although scientists have considered such a scenario for decades, the calculations involved have been forbidding. But in the Nov. 29 issue of the journal Science, Quinn and his team reported simulating one million clouds of gas, each one-thirtieth of an Earth mass, at one-hour intervals as they interacted gravitationally for up to 350 years.

"We used a fraction of the machine at the Pittsburgh Supercomputing Center (at Carnegie-Mellon University) for a solid several weeks. It's roughly like having 100 of the fastest Pentium computers all running the same calculations for a couple of weeks," Quinn said.

Refining the calculations took nearly two years, he added. The results suggest gas giants can grow in fewer than 1,000 years, and accumulate masses similar to those spotted around other stars.

Planetary scientist Jack Lissauer of NASA Ames Research Center in Moffett Field, Calif., remains skeptical.

"It's not that I think the calculations are bad. They're the best calculations on this facet of the problem that have ever been done," he said. However, Lissauer said, for planets to form this quickly, the disks from which they emerge need to be very unstable, and before any forming planet reached that stage slight instabilities would cause spiral waves to flatten out any clumps.

Also, Quinn said, the computer model does not explain how rocklike planets such as Earth form, for which the standard model can provide an answer. Neither model yet can explain why so many planets seen outside our solar system orbit so close to their stars, he added.

"Do I think this work is an important advance? Yes. Do I think it is definitive? No," said computational astrophysicist Richard Durisen of Indiana University in Bloomington. He and Quinn said future calculations need to take better account of the extremely complex role temperature plays.

"That's actually quite hard," Quinn explained, noting it would require at least 2-to-10 times more computing power. "Fortunately, computers always get faster, so that makes it doable in a year's time or whenever," he said.


(Reported by Charles Choi, UPI Science News, in New York)

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