Significance Jupiter is the most massive planet of the Solar System and its presence had an immense effect on the dynamics of the solar accretion disk. Knowing the age of Jupiter, therefore, is key for understanding how the Solar System evolved toward its present-day architecture. However, although models predict that Jupiter formed relatively early, until now, its formation has never been dated. Here we show through isotope analyses of meteorites that Jupiter’s solid core formed within only ∼1 My after the start of Solar System history, making it the oldest planet. Through its rapid formation, Jupiter acted as an effective barrier against inward transport of material across the disk, potentially explaining why our Solar System lacks any super-Earths.

Understanding core formation in meteorite parent bodies is critical for constraining the fundamental processes of protoplanet accretion and differentiation within the solar protoplanetary disk. We report variations of 5 to 20 parts per million in (182)W, resulting from the decay of now-extinct (182)Hf, among five magmatic iron meteorite groups. These (182)W variations indicate that core formation occurred over an interval of ~1 million years and may have involved an early segregation of Fe-FeS and a later segregation of Fe melts. Despite this protracted interval of core formation, the iron meteorite parent bodies probably accreted concurrently ~0.1 to 0.3 million years after the formation of Ca-Al-rich inclusions. Variations in volatile contents among these bodies, therefore, did not result from accretion at different times from an incompletely condensed solar nebula but must reflect local processes within the nebula.

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