The origin of giant exoplanets on short-period orbits is a key open question in planetary science. Measurements of the atmospheric composition of these planets can reveal crucial information on the planetary origin. We show that the two leading formation scenarios for hot/warm Jupiters: formation in the outer disk followed by migration and in-situ formation, lead to significant differences in the predicted atmospheric composition.
We use N-body simulations of planetesimal accretion for various planetary formation locations, planetary masses, as well as planetesimal sizes, and estimate the accreted heavy-element mass and final planetary composition for these two formation models. We find that migrating giant planets are much more metal-rich than giant planets that form in-situ. The refractory-to-volatile ratio is 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. This study highlights the importance of measuring the atmospheric composition of warm Jupiters and its potential to reveal the planetary origin.