Alan Boss

Carnegie Institute of Washington

Gas Giant Planet Formation: Core Accretion or Disk Instability
 
Now that suspected gas giant planets have been detected around
nearby stars, mechanisms for their formation merit re-examination.   
Two mechanisms have been suggested for forming gas giant planets,    
core accretion and disk instability. Core accretion begins with the  
runaway growth of a roughly 10 Earth-mass solid core, followed by the
accretion of disk gas to form the planet's envelope. Core accretion
is the generally accepted mechanism, but if a disk instability is
possible, it will occur well before core accretion does. Disk
instability involves a self-gravitational instability of the
gaseous portion of the protoplanetary disk, and can occur within
a few thousand years. Each mechanism has a number of drawbacks
and advantages, making a choice purely on theoretical grounds
difficult, but a relatively clear-cut observational test can
distinguish between these two theoretical mechanisms.