Issue |
A&A
Volume 654, October 2021
|
|
---|---|---|
Article Number | A83 | |
Number of page(s) | 32 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202141467 | |
Published online | 15 October 2021 |
Future destabilisation of Titan as a result of Saturn’s tilting
1
IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université de Lille,
75014
Paris,
France
e-mail: melaine.saillenfest@obspm.fr
2
Department of Mathematics, University of Pisa,
Largo Bruno Pontecorvo 5,
56127
Pisa,
Italy
Received:
4
June
2021
Accepted:
6
July
2021
Context. As a result of Titan’s migration and Saturn’s probable capture in secular spin–orbit resonance, recent works show that Saturn’s obliquity could be steadily increasing today and may reach large values in the next billions of years. Satellites around high-obliquity planets are known to be unstable in the vicinity of their Laplace radius, but the approximations used so far for Saturn’s spin axis are invalidated in this regime.
Aims. We aim to investigate the behaviour of a planet and its satellite when the satellite crosses its Laplace radius while the planet is locked in secular spin–orbit resonance.
Methods. We expand on previous works and revisit the concept of Laplace surface. We use it to build an averaged analytical model that couples the planetary spin-axis and satellite dynamics.
Results. We show that the dynamics is organised around a critical point, S1, at which the phase-space structure is singular, located at 90° obliquity and near the Laplace radius. If the spin-axis precession rate of the planet is maintained fixed by a resonance while the satellite migrates outwards or inwards, then S1 acts as an attractor towards which the system is forced to evolve. When it reaches the vicinity of S1, the entire system breaks down, either because the planet is expelled from the secular spin–orbit resonance or because the satellite is ejected or collides into the planet.
Conclusions. Provided that Titan’s migration is not halted in the future, Titan and Saturn may reach instability between a few gigayears and several tens of gigayears from now, depending on Titan’s migration rate. The evolution would destabilise Titan and drive Saturn towards an obliquity of 90°. Our findings may have important consequences for Uranus. They also provide a straightforward mechanism for producing transiting exoplanets with a face-on massive ring, a configuration that is often put forward to explain some super-puff exoplanets.
Key words: planets and satellites: dynamical evolution and stability / planets and satellites: formation / celestial mechanics
© M. Saillenfest and G. Lari 2021
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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