Quantitative Links between Formation and Atmospheric Composition for Giant Planets

Abstract

Precise atmospheric abundances of giant exoplanets are becoming increasingly prevalent and there is a need to systematically convert these measurements into metrics that inform us about the planets' accretion history. We present a quantitative framework for relating atmospheric composition to the accretion of metals and primordial gas. This includes i) new relations that simplify and generalize the connection between atmospheric metallicity and metal mass fraction, ii) methods for inferring the source of the metals and quantifying the quantity of metals accreted via different sources, and iii) relating the derived quantities to expectations from formation models. We also derive a new estimate of the minimum disk mass needed to form a planetary system based on the amount of excess metals accreted by a planet, assuming that this excess originates from the drift and evaporation of pebbles at condensation fronts. This paper is accompanied by an open-source code that implements the methods presented herein.