Constraining the origin of giant exoplanets via elemental abundance measurements

TL;DR

This study compares two main formation models for giant exoplanets by analyzing their atmospheric compositions, revealing significant differences in metallicity and elemental ratios that can help determine their origins.

Contribution

The paper introduces a method to distinguish planet formation scenarios by analyzing atmospheric elemental abundances and metallicity trends in warm Jupiters.

Findings

Migrating planets have 2-14 times higher metallicities than in situ formed planets.

Refractories to volatiles ratio is above one for migrating planets, below 0.4 for in situ planets.

Metallicity increases with decreasing planetary mass for migrating planets, remains constant for in situ formation.

Abstract

The origin of close-in giant planets is a key open question in planet formation theory. The two leading models are (i) formation at the outer disk followed by migration and (ii) in situ formation. In this work we determine the atmospheric composition of warm Jupiters for both formation scenarios. We perform N-body simulations of planetesimal accretion interior and exterior to the water ice-line for various planetary formation locations, planetary masses, and planetesimal sizes to estimate the accreted heavy-element mass and final planetary composition. We find that the two models differ significantly: migrating giant planets have 2-14 times higher metallicities than planets that form in situ. The ratio between refractories and volatiles is found to be above one for migrating planets but below 0.4 for planets that form in situ. We also identify very different trends between heavy-element enrichment and planetary mass for these two formation mechanisms. While the metallicity of migrating planets is found to increase with decreasing planetary mass, it is about constant for in situ formation. Our study highlights the importance of measuring the atmospheric composition of warm Jupiters and its connection to their formation and evolutionary paths.