PureInsight | January 6, 2003
[PureInsight.org] The November 29th edition of Science magazine featured a report entitled, "Formation of Giant Planets by Fragmentation of Protoplanetary Disks." A research team led by Dr. Lucio Mayer from the Department of Astronomy at University of Washington in Seattle, Washington studied the evolution of gravitationally unstable protoplanetary gaseous disks by using three-dimensional smoothed particle hydrodynamics simulations, which allowed unprecedented resolution . In the simulations it required only a few orbits of protoplanetary gaseous disks, or several hundred years, to form giant planets. The discovery has disproved the core-accretion model, which maintained that it required several millions of years for giant planets to form, as the sole model for planet formation.
These researchers were able to show that persistent protoplanets with self gravity could arise after a few disk orbital periods if cooling was efficient enough to maintain the temperature close to 50 K. The resulting bodies would have masses and orbital eccentricities similar to those of detected extrasolar planets.
But in the standard core-accretion model, giant planets might require longer to form than observed disk lifetimes. For example, more than 80% of the stars in the galaxy probably formed in dense clusters like those in the Orion nebula where the ultraviolet radiation of bright stars can ablate gaseous disks in far less than a million years. So giant planet formation must occur quickly, or such planets would be rare.
Such planets are not very rare. Since the late 1990's about 100 extrasolar planets have been detected by the wobble they induce on their stars with masses ranging from about one Jupiter mass (MJ) to more than 10 MJ. All of these planets were formed by the gravitational instability of the protoplanetary gaseous disks, which supports the findings from the simulation studies.
 "Formation of Giant Planets by Fragmentation of Protoplanetary Disks" by Lucio Mayer, Thomas Quinn, James Wadsley, and Joachim Stadel, Science 2002 November 29; 298: 1756-1759
Translated from: http://www.zhengjian.org/zj/articles/2002/12/3/19507.html