Resonance locking as the source of rapid tidal migration in the Jupiter and Saturn moon systems

TL;DR

This paper proposes resonance locking as a key mechanism explaining rapid tidal migration of Jupiter and Saturn's moons, aligning with observed effective Q values and solving existing discrepancies in moon system evolution and heating.

Contribution

It introduces resonance locking as a novel explanation for moon migration rates, linking planetary internal evolution to observed tidal dissipation effects.

Findings

Resonance locking can produce rapid outward moon migration.

Effective Q values vary between moons and over time, consistent with resonance locking.

Resonance locking explains small Q for Rhea and high heating for Enceladus.

Abstract

The inner moons of Jupiter and Saturn migrate outwards due to tidal energy dissipation within the planets, the details of which remain poorly understood. We demonstrate that resonance locking between moons and internal oscillation modes of the planet can produce rapid tidal migration. Resonance locking arises due to the internal structural evolution of the planet and typically produces an outward migration rate comparable to the age of the solar system. Resonance locking predicts a similar migration timescale but a different effective tidal quality factor $Q$ governing the migration of each moon. It also predicts nearly constant migration timescales a function of semi-major axis, such that effective $Q$ values were larger in the past. Recent measurements of Jupiter and Saturn's moon systems find effective $Q$ values that are smaller than expected (and are different between moons), and which correspond to migration timescales of $\sim$10 Gyr. If confirmed, the measurements are broadly consistent with resonance locking as the dominant source of tidal dissipation in Jupiter and Saturn. Resonance locking also provides solutions to several problems posed by current measurements: it naturally explains the exceptionally small $Q$ governing Rhea's migration, it allows the large heating rate of Enceladus to be achieved in an equilibrium eccentricity configuration, and it resolves evolutionary problems arising from present-day migration/heating rates.