Studying the orbits of thousands of exoplanets shows that large planets tend to have elliptical orbits, while smaller planets tend to have more circular orbits. This split coincides with several other classic features in the exoplanet population, such as the high abundance of small planets over large planets and a tendency for giant planets to only form around stars enriched in heavy elements such as oxygen, carbon and iron. The finding points toward two distinct pathways for forming small and large planets.
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