Paper detail

Capture and escape from the 2:1 resonance between Ariel and Umbriel in a fast-migration scenario of the Uranian system

Recent measurements suggest that Uranus may exhibit a higher tidal dissipation than previously assumed. This enhanced dissipation leads to a faster orbital migration of its five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon. Consequently, resonant encounters that have always been discarded in previous works need to be included. In particular, Ariel's fast migration implies that the crossing of the 2:1 mean motion resonance with Umbriel is extremely likely and it could have occurred in recent times. Capture into this strong resonance would have induced significant tidal heating within Ariel, possibly explaining its resurfacing. Therefore, in this work, we aim to explore the orbital history of the Uranian moons in a context of fast tidal migration, including the crossing of the 2:1 mean motion resonance between Ariel and Umbriel. For small initial eccentricities, we confirm that the moons are always captured into this resonance. As the system is not currently involved in any mean motion resonance, we investigated possible dynamical mechanisms for exiting the 2:1 resonance. We show that the resonance could have been broken by a further resonant encounter with Titania. We analyzed the crossing of the 4:2:1 and 3:2:1 resonant chains, and looked for the parameter space where the probability of escaping the resonance is maximized. Taking a dissipative parameter of Ariel $k_{2,2}/Q_2<10^{-3}$, the passage through the 3:2:1 resonance succeeds in disrupting the 2:1 Ariel-Umbriel mean motion resonance in more than $60\%$ of our numerical experiments. A fraction of our simulations results in final low eccentricities and inclinations, which can eventually match the current orbital features of the system. As the proposed orbital history requires specific ranges of the dissipative parameters for the system, future Uranus mission data will validate (or disprove) this scenario.