Popular Solar System Orbits Result in 'Planet Pileups'
"Our results show that the final distribution of planets does not vary smoothly with distance from the star, but instead has clear 'deserts' -- deficits of planets -- and 'pileups' of planets at particular locations," said Ilaria Pascucci, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory.
"Our models offer a plausible explanation for the pileups of giant planets observed recently detected in exoplanet surveys," said Richard Alexander of the University of Leicester in the United Kingdom.
Alexander and Pascucci identified high-energy radiation from baby sun-like stars as the likely force that carves gaps in protoplanetary disks, the clouds of gas and dust that swirl around young stars and provide the raw materials for planets. The gaps then act as barricades, corralling planets into certain orbits.
The exact locations of those gaps depend on the planets' mass, but they generally occur in an area between 1 and 2 astronomical units from the star. One astronomical unit, or AU, marks the average distance from the Earth to the sun. The findings are to be published in the journal Monthly Notices of the Royal Astronomical Society.
According to conventional wisdom, a solar system starts out from a cloud of gas and dust. At the center of the prospective solar system, material clumps together, forming a young star. As the baby star grows, its gravitational force grows as well, and it attracts dust and gas from the surrounding cloud.
Accelerated by the growing gravitation of its star, the cloud spins faster and faster, and eventually flattens into what is called a protoplanetary disk. Once the bulk of the star's mass has formed, it is still fed material by its protoplanetary disk, but at a much lower rate.
"For a long time, it was assumed that the process of accreting material from the disk onto the star was enough to explain the thinning of the protoplanetary disk over time," Pascucci explained. "Our new results suggest that there is another process at work that takes material out of the disk."
Pascucci presented the findings at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas on March 19.
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