Answer Happy

3.2 (a) Briefly describe the Core Accretion model for gas giant planet formation. What is the "snow line" in a proto-planetary disk, and how might this critically assist gas-giant formation? (include discussion of timescales). (b) The feeding rate for a solid planetary embryo (M, R.) sweeping through a volume of planetesimals is given by dM =R2(1+2GM (3.33) where , is the mass density of planetesimals and v is the relative velocity of the embryo and the planetesimals. By referring to the components of this equation, demonstrate the orderly and runaway growth regimes for a planet embryo. Give two physical arguments for why runaway growth must eventually slow down. (c) Describe the physical mechanism which can make ~1 meter planetesimals migrate inwards in a gas disk. Describe the (different) physical mechanisms by which a large proto-planet can migrate inwards. As a planetary embryo accretes planetesimals its mean density is likely to increase as its self-gravity compresses the "rubble pile" of material. In the case of water ice the compression can also change the ice phase and increase the mean density of the embryo. How would such a change in mean density alter the subsequent growth rate of the embryo?