Swirling eddies and chaotic vortices are crucial to the formation of new planets, suggests a counterintuitive new study.
Such turbulence is vital to helping planets go from "toddler" to "teenage" size by helping rocks and boulders stick together, the computer simulation hints.
A few scientists recently suspected that turbulence might help in planet formation, but no one had showed in detail how that might work until now.
"We were the first to model how interacting boulders move around in this turbulence," said Anders Johansen of the Max Planck Institute for Astronomy in Germany, who led the research team that made the new findings. The study appeared last week in the journal Nature.
The research showed that turbulence could create "planetesimals," or planetary precursors, very quickly—in only seven orbits around a star, or around just a hundred years.
New solar systems form from a swirling disk of dust and gas surrounding a central star. (Related: "Planet-Forming Disk Spotted Around Dead Star" [April 5, 2006].)
As the matter swirls around, microscopic bits of dust hit each other and stick together. Gradually they can gather into rocks and boulders, around a yard (a meter) across.
"We have a pretty good grasp of this [process]," Johansen said.
But explaining how matter forms bigger clumps—up to planetesimals about a kilometer across—has eluded scientists.
"That has been known to be a big problem for the last 30 years," Johansen said.
Part of the issue is that when larger boulders collide with each other, "they don't stick to each other very well, but are likely to destroy each other when they collide," Johansen said.
And around this size, the rocks would begin to experience drag from the gas around them.
In the new computer model, scientists studied what would happen if this disk of orbiting matter does not spin calmly around but instead has turbulence stirring things up.
Although researchers haven't figured out for sure what might cause such turbulence, they're confident that there would be a fair amount of it in the disks surrounding young stars.
The turbulence has high-pressure areas where boulders tend to accumulate, the simulation revealed.
Once a few boulders get stuck together in such locations, the formation can help other boulders stick too, since they shield each other from the gas.
The areas also help the boulders resist the headwind from the gas around them, like "drafting" racers...
Gravity would then pull the boulders closer together, until they gradually collapsed into planetesimals a couple of hundred miles (a few hundred kilometers) across.
Planetesimals that large would attract even more rocks with their gravity, allowing them to grow into full-fledged planets...
"It's kind of ironic," Throop said. "We're used to explaining things on the size of galaxies, and on really small scales the size of light waves.
"In planetesimal formation, however, the tricky part is these medium-sized grains," around a yard (a meter) across, he added.
This new study is "a big step," Throop said, toward figuring out how budding planetesimals pass through their "toddler" stage and grow to full-size planets.
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