Formation of Solar and Extrasolar Giant Planets by Core-Nucleated Accretion

Grant #: NNX10AT01A
Senior Scientist: Gennaro D’Angelo

The objective of the proposed research is the improvement of the understanding of gas giant planet formation through the Core-Nucleated Accretion model, based on constraints derived from solar and extrasolar planet observations. More specifically, we will determine:

(1) the physical conditions in a protoplanetary disk that may lead to the formation of gas giant planets;

(2) the effects of planetary migration on realistic planet formation models, when disk evolution is taken into account;

(3) the luminosities and other observable properties of giant planets formed through core-nucleated accretion, which will help the characterization of young planet candidates detected via imaging techniques;

(4) the thermal conditions in the regions of regular satellite formation around Solar System giant planets; (5) constraints on the initial orbital radii of the four giant planets in the Solar System. 

We will pursue these objectives mainly by means of numerical modeling. A number of state-of-the-art codes will be employed to model in detail different processes at various stages of the planet’s growth. (1) A multi-zone solids’ accretion code will be used to model formation of the solid core. This approach will allow us to account, among other effects, for the orbital spacing of potential competing cores. (2) A planet formation code that includes a large number of physical effects will be used to model the planet evolution until gas accretion ends. The code computes the thermal structure of the envelope, taking into account the energy deposited by accreted solids. The opacity of dust grains is computed in a new and self-consistent fashion that accounts for coagulation and settling of dust grains in the envelope. Therefore, we will be able to obtain more accurate estimates of the time scales for the accumulation of the envelope and the onset of runaway gas accretion. (3) A 3-D high-resolution, hydrodynamics code will provide gas accretion rates during runaway gas growth, when a giant planet rapidly grows in mass, acquiring most of its gas contents. During this phase, tidal interactions with the protoplanetary disk are no longer negligible and, in fact, they will limit the gas accretion rate onto the planet. 3-D calculations will also provide density distributions of torques that will be used to model planetary migration under a range of protoplanetary disk conditions, by combining results from the planet formation code and 1-D disk evolution code. The 3-D code will also be used to study the thermal conditions in protosatellite disks and the evolution of multiple giant planets in a protoplanetary disk. (4) A non-gray atmosphere code will model the isolation phase of a giant planet, when planet evolves at a constant mass by cooling and contracting. These calculations will allow us to predict observables of young giant planets that will aid in the interpretation of directly imaged planetary mass objects and permit more conservative determinations of the masses assigned to young planetary candidates. The significance of this work rests on its potential to deliver a framework for the interpretation of the observations of solar and extrasolar giant planets.