Giant Planet Formation: Critical Mass and Multiple Equilibira
Abstract
Presented results are continuation of the effort to clarify important concept of the giant planet formation, namely the so-called critical mass, necessary to permanently attract gas of the protoplanetary nebula to a terrestrial-planet-like, heavy element core. We approximate the protoplanet as a spherically symmetric, isothermal, self-gravitating gas envelope in equilibrium around a rigid body of given mass and density, with the gaseous envelope required to fill the Hill Sphere. Equilibria are calculated without apriori determination of total protoplanet mass or nebula density, starting only with core of given mass, and an envelope gas density at the core surface. We compare results obtained with several different analytic forms of the gas equations of state. Our models predict two types of envelope equilibria: `uniform', with density of envelope gas dropping weakly with increase in radial distance, and `compact', having a small, but very dense gas layer wrapped around the core, and very low gas density further out. Critical core masses range from fraction of the Earth mass to several Earth masses, depending on the gas EOS used. Furthermore, our solutions show a wide range of possible envelopes. This variety is a consequence of the envelope's self-gravity. We show that multiple planetary equilibria exist for given nebula conditions. Not all of these can be reached along a hydrostatic sequence of models. For a given core, multiple solutions exist, that fit into the same nebula, and some of them also have equal envelope mass. Above the critical mass only `compact' solutions exist. Finally, stability of the equilibria is critically dependant on the details of the gas parameters.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....13483P