DETERMINING THE METALLICITY OF GIANT PLANETS IN MESA WITH HIGH-PRESSURE METAL CORES

Abstract

We implement new equations of state into MESA to simulate planet cores as a way of modeling high metallicity in giant planets by treating the metal content of a planet as a high-pressure core. We construct a grid of planet models spanning planet mass, metallicity, and incident flux, and evolve each model along with its core in time. Interpolating off of the grid of MESA models, we determine the individual metallicity of 47 “cool” Jupiter exoplanets with surface equilibrium temperatures below 1000 K. We find metal fractions ranging from zero and almost zero among high-mass planets up to above 90% among low-mass planets. The metal mass for all fitted planets in the sample are then used to fit a relationship for metallicity as a sole function of planet mass. We find the relation Mcore = (28.5±6.43)Mpl (0.302±0.122), where Mcore has units of ML and Mpl has units of Mjup. Issues in determining metallicity uncertainty prevent comparison to other mass-metallicity relationships, but the method of determining individual planet metallicity in MESA has applications for simulating hot Jupiters and other giant planets where metal content is significant.