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

¹ Department of Mathematics, University of Pisa, Largo Bruno Pontecorvo 5, 56127 Pisa, Italy
² Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098, XH, Amsterdam, The Netherlands
³ LTE, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Lille, LNE, CNRS, 61 Avenue de l’Observatoire, 75014 Paris, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 September 2025
Accepted: 15 November 2025

Abstract

Recent measurements and theoretical developments 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, when studying their orbital evolution, resonant encounters that were always 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 (within the last one billion years). Capture into this strong resonance would have induced significant tidal heating within Ariel, possibly explaining its resurfacing. Therefore, for this work, we explored 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 low initial eccentricities, we confirm that the moons are always captured into this resonance, which can potentially persist indefinitely. 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. In particular, taking a dissipative parameter of Ariel k_2,2/Q₂ < 10⁻³, the passage through the 3:2:1 resonance succeeds in disrupting the 2:1 mean motion resonance between Ariel and Umbriel in more than 60% of our numerical experiments. While the crossing of the three-body resonant chain produces a general excitation of the orbital elements of all moons, 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, it will be possible to validate (or disprove) this scenario with the data of the next space mission to Uranus.