Inclination damping on Callisto

TL;DR

This paper investigates why Callisto retains its inclination despite expected damping, proposing recent orbital excitation through resonance with Ganymede as the cause, supported by tidal dissipation estimates.

Contribution

It introduces a model explaining Callisto's current inclination via recent resonance-induced excitation, contrasting with prior assumptions of primordial origin.

Findings

Callisto's inclination was excited ~0.3 Gyr ago.

Resonance with Ganymede caused orbital excitation.

Estimated tidal quality factors: k2/Q~0.05 for Callisto.

Abstract

Callisto is thought to possess a subsurface ocean, which will dissipate energy due to obliquity tides. This dissipation should have damped any primordial inclination within 1 Gyr - and yet Callisto retains a present-day inclination. We argue that Callisto's inclination and eccentricity were both excited in the relatively recent past (~0.3 Gyr). This excitation occurred as Callisto migrated outwards according to the "resonance-locking" model and passed through a 2:1 mean-motion resonance with Ganymede. Ganymede's orbital elements were likewise excited by the same event. To explain the present-day orbital elements we deduce a solid-body tidal k2/Q~0.05 for Callisto and a significantly lower value for Ganymede.