Formation of Giant Planets and sub-Neptunes by Core-Nucleated Accretion

Grant #: NNX14AH78A
Senior Scientist: Gennaro D’Angelo

The basic objective of this proposal is the improvement of the understanding of the origin and evolution of planets with gaseous envelopes, including gas giants and “sub-Neptunes”, as observed in extrasolar systems. The project will involve numerical modelling and comparison of the results with observations of planets by radial velocities, transits, and direct detections. The calculations will be based on giant and sub-Neptune planet formation through the Core-Nucleated Accretion model (CNA), in which a heavy-element core forms first. Once it has attained sufficient mass, it captures gas from the protoplanetary disk as it continues to accrete solids. Significant improvements in the physics, compared with past work, will be incorporated. Specifically, we will address the following questions:

(1) What is the formation history of a Neptune-type planet formed in the inner disk, within 2 AU of its star, as a function of position of the planet in the disk and the disk properties?

(2) Can the sub-Neptune planets, to date observed primarily within 1 AU from their star, be best explained through formation at greater distances followed by orbital migration, or by in situ formation?

(3) Is the observed mass-radius relation, for the Neptune-size planets for which both have been observed, consistent with formation by CNA?

(4) Can the observed properties, such as luminosities and effective temperatures, of directly-detected extrasolar planets be explained by CNA models?

To address these questions, a number of state-of-the-art codes will be employed to model in detail different processes at various stages of theplanet’s growth. A multi-zone accretion code will be used to improve the model for accretion of planetesimals onto the planet. A planet formation code that includes a large number of physical effects will be used to model the planet evolution until gas accretion ends. A 3-D high-resolution radiation-hydrodynamics code, which calculates gas accretion rates onto a planet embedded in and interacting with a disk, will provide gas accretion rates during runaway gas growth.