Dynamical evolution of the Uranian satellite system II. Crossing of the 5/3 Ariel–Umbriel mean motion resonance

Abstract

At present, the main satellites of Uranus are not involved in any low order mean motion resonance (MMR). However, owing to tides raised in the planet, Ariel and Umbriel most likely crossed the 5/3 MMR in the past. Previous studies on this resonance passage relied on limited time-consuming $N-$body simulations or simplified models focusing solely on the effects of the eccentricity or the inclination. In this paper, we aim to provide a more comprehensive view on how the system evaded capture in the 5/3 MMR. For that purpose, we developed a secular resonant two-satellite model with low eccentricities and low inclinations, including tides using the weak friction model. By performing a large number of numerical simulations, we show that capture in the 5/3 MMR is certain if the initial eccentricities of Ariel, $e_1$, and Umbriel, $e_2$, are related through ${(e_1^2+e_2^2)}^{1/2}<0.007$. Moreover, we observe that the eccentricity of Ariel is the key variable to evade the 5/3 MMR with a high probability. We determine that for $e_1>0.015$ and $e_2<0.01$, the system avoids capture in at least 60% of the cases. We also show that, to replicate the currently observed system, the initial inclinations of Ariel and Umbriel must lay within $I_1\le 0.05°$ and $0.06°\le I_2\le 0.11°$, respectively. We checked these results using a complete $N-$body model with the five main satellites and did not observe any significant differences.