Why Callisto Was Excluded: The Pressure Bump Trap That Saved the Laplace Resonance

Why Callisto Never Joined the Laplace Dance: A Pressure-Bump Escape Story Core question: If Io, Europa, and Ganymede can lock into the 4:2:1 Laplace resonance, why is Callisto left out? One-sentence answer: A pressure bump in the circum-Jovian disk acted as a migration trap, parking Callisto outside the resonant chain and removing the need for it to form late or slowly. Quick Scan N-body experiments show that a bump of intermediate aspect ratio (∆h/w ≈ 0.45–0.6) naturally stalls Callisto while letting the other three moons migrate inward and lock into resonance. A public, ready-to-run parameter set is provided for researchers …