Early Jupiter's Hybrid Migration: Resolving the Asteroid Belt's Compositional Dichotomy

The asteroid belt, located between Mars and Jupiter, serves as a crucial fossil record of the early solar system's dynamics and compositional gradient. A significant feature of this region is its pronounced compositional dichotomy, characterized by a predominance of S-type (silicaceous) asteroids in the inner belt and C-type (carbonaceous) asteroids in the outer belt. This study proposes and investigates a novel "hybrid migration" model for early Jupiter, characterized by an initial phase of inward migration followed by a subsequent outward migration, to resolve this dichotomy. While the Grand Tack hypothesis proposed a similar two-phase migration, our "hybrid migration" model focuses on comprehensively quantifying the planetesimal scattering and capture mechanisms and their direct impact on establishing the observed compositional gradient. Through extensive N-body simulations incorporating planetesimal scattering and accretion processes, we demonstrate that Jupiter's dynamic movement effectively redistributes material from both the inner and outer regions of the protoplanetary disk into the primordial asteroid belt. The inward migration phase efficiently scatters inner solar system planetesimals, enriched in refractory materials, towards the asteroid belt. Subsequently, Jupiter's outward migration disperses outer solar system planetesimals, rich in volatiles and organic compounds, into the same region. This two-phase process naturally accounts for the intermixing and the establishment of the observed compositional gradient, where material originating from the inner solar system preferentially populates the inner asteroid belt, and material from beyond Jupiter's initial formation region dominates the outer belt. Our results provide compelling evidence that a hybrid migration scenario for Jupiter is a robust mechanism for shaping the early solar system's architecture and reconciling the long-standing mystery of the asteroid belt's compositional diversity. This model offers new insights into the coupled evolution of giant planets and small body populations.