The Critical Core Mass of Rotating Planets

TL;DR

This paper investigates how planetary rotation influences the critical core mass necessary for gas giant formation, considering various boundary conditions and internal structures, revealing that rotation significantly affects planetary evolution.

Contribution

It provides a detailed analysis of the impact of rotation on the critical core mass, incorporating different boundary conditions and internal layer properties, which was previously less understood.

Findings

Critical core mass depends on polytrope stiffness and boundary conditions.

Rotation increases critical core mass with higher core density.

Thinner radiative layers lead to higher critical core mass in Hill boundary models.

Abstract

The gravitational harmonics measured from Juno and Cassini spacecrafts help us to specify the internal structure and chemical elements of Jupiter and Saturn, respectively. However, we still do not know much about the impact of rotation on the planetary internal structure as well as their formation. The centrifugal force induced by rotation deforms the planetary shape and partially counteracts the gravitational force. Thus, rotation will affect the critical core mass of the exoplanet. Once the atmospheric mass becomes comparable to the critical core mass, the planet will enter the runaway accretion phase and becomes a gas giant. We have confirmed that the critical core masses of rotating planets depend on the stiffness of the polytrope, the outer boundary conditions, and the thickness of the isothermal layer. The critical core mass with Bondi boundary condition is determined by the surface properties. The critical core mass of a rotating planet will increase with the core gravity (i.e., the innermost density). For the Hill boundary condition, the soft polytrope shares the same properties as planets with Bondi boundary condition. Since the total mass for planets with Hill boundary condition increases with the decrease of the polytropic index, higher core gravity is required for rotating planets. As a result, the critical core mass in the stiff Hill model sharply increases. The rotation effects become more important when the radiative and convective regions coexist. Besides, the critical core mass of planets with Hill (Bondi) boundary increases noticeably as the radiative layer becomes thinner (thicker).