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How did giant-planet migration mix material in the asteroid belt?

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Illustration showing a massive asteroid above a city map with a dinosaur silhouette for scale, highlighting the asteroid's size compared to major urban areas. — Asteroid This rock would take out more than just a *T. rex*.

During the early history of the solar system, the migration of giant planets—specifically Jupiter and Saturn—played a critical role in mixing material within the asteroid belt.

According to dynamical models, this process occurred in two primary phases:

Inward Migration: As the giant planets migrated toward the Sun, they disrupted the region of the current asteroid belt, scattering the primordial planetesimals throughout the solar system and halting their accretion.
Outward Migration: As the planets moved back outward to their present-day positions, they repopulated the asteroid belt with a mixture of material originating from both the inner and outer solar system.

This "grand tack" migration explains why the modern asteroid belt contains a diverse population of both rocky and icy asteroids. While the belt continues to evolve today through collisions and the effects of solar radiation, the initial mixing was a direct consequence of these large-scale planetary movements.12