A model of Saturn inferred from its measured gravitational field

Abstract

We present an interior model of Saturn with an ice-rock core, a metallic region, an outer molecular envelope and a thin transition layer between the metallic and molecular regions. The shape of Saturn’s 1 bar surface is irregular and determined fully self-consistently by the required equilibrium condition. While the ice-rock core is assumed to have a uniform density, three different equations of state are adopted for the metallic, molecular and transition regions. The Saturnian model is constrained by its known mass, its known equatorial and polar radii, and its known zonal gravitational coefficients, J2n, n = 1, 2, 3. The model produces an ice-rock core with equatorial radius 0.203 RS, where RS is the equatorial radius of Saturn at the 1-bar pressure surface; the core density ρc = 10388.1 kgm−3 corresponding to 13.06 Earth masses; and an analytical expression describing the Saturnian irregular shape of the 1-bar pressure level. The model also predicts the values of the higher-order gravitational coefficients, J8, J10 and J12, for the hydrostatic Saturn and suggests that Saturn’s convective dynamo operates in the metallic region approximately defined by 0.2 RS < re < 0.7 RS, where re denotes the equatorial radial distance from the Saturnian center of figure.