The future large obliquity of Jupiter

Saillenfest, Melaine; Lari, Giacomo; Courtot, Ariane

doi:10.1051/0004-6361/202038432

Cited by 20 publications

(44 citation statements)

References 64 publications

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“…In order to explore the long-term dynamics of Saturn's spin axis, we need an orbital solution that is valid over billions of years. In the same way as Saillenfest et al (2020), we use the secular solution of Laskar (1990) expanded in quasi-periodic series:…”

Section: Orbital Solutionmentioning

confidence: 99%

“…For the giant planets of the Solar System, the existing secular spin-orbit resonances are small and isolated from each other, and only first-order resonances play a substantial role (see e.g. Saillenfest et al 2020).…”

Section: Orbital Solutionmentioning

confidence: 99%

“…As pointed out by Saillenfest et al (2020), one must be careful about the normalisation used for λ. Here, we adopt R eq = 60268 km by convention and we renormalise each quantity in Eqs.…”

Section: Precession Constantmentioning

confidence: 99%

“…This will provide the whole region of the parameter space allowing Titan's migration to be responsible for Saturn's large obliquity, with the corresponding probability. Finally, since Titan still migrates today, Saturn's obliquity could suffer from further large variations in the future, in the same way as Jupiter (Saillenfest et al 2020). Therefore, we also aim to extend previous analyses to the future dynamics of Saturn's spin axis.…”

Section: Introductionmentioning

confidence: 99%

“…Because of this mechanism, dramatic variations in the Earth's obliquity are expected to take place in a few billion years from now, as a result of the Moon's migration (Néron de Surgy & Laskar 1997). Likewise, Jupiter's obliquity is likely steadily increasing today and could exceed 30 • in the next billions of years, as a result of the migration of the Galilean satellites (Lari et al 2020;Saillenfest et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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The past and future obliquity of Saturn as Titan migrates

Saillenfest

Lari

Boué

et al. 2021

A&A

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Context. Giant planets are expected to form with near-zero obliquities. It has recently been shown that the fast migration of Titan could be responsible for the current 26.7°-tilt of Saturn’s spin axis. Aims. We aim to quantify the level of generality of this result by measuring the range of parameters allowing for this scenario to happen. Since Titan continues to migrate today, we also aim to determine the obliquity that Saturn will reach in the future. Methods. For a large variety of migration rates for Titan, we numerically propagated the orientation of Saturn’s spin axis both backwards and forwards in time. We explored a broad range of initial conditions after the late planetary migration, including both small and large obliquity values. Results. In the adiabatic regime, the likelihood of reproducing Saturn’s current spin-axis orientation is maximised for primordial obliquities between about 2° and 7°. For a slightly faster migration than expected from radio-science experiments, non-adiabatic effects even allow for exactly null primordial obliquities. Starting from such small tilts, Saturn’s spin axis can evolve up to its current state provided that: (i) the semi-major axis of Titan changed by more than 5% of its current value since the late planetary migration, and (ii) its migration rate does not exceed ten times the nominal measured rate. In comparison, observational data suggest that the increase in Titan’s semi-major axis exceeded 50% over 4 Gyr, and error bars imply that the current migration rate is unlikely to be larger than 1.5 times its nominal value. Conclusions. If Titan did migrate substantially before today, tilting Saturn from a small obliquity is not only possible, but it is the most likely scenario. Saturn’s obliquity is still expected to be increasing today and could exceed 65° in the future. Maximising the likelihood would also put strict constraints on Saturn’s polar moment of inertia. However, the possibility remains that Saturn’s primordial obliquity was already large, for instance as a result of a massive collision. The unambiguous distinction between these two scenarios would be given by a precise measure of Saturn’s polar moment of inertia.

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Section: Orbital Solutionmentioning

confidence: 99%

Section: Orbital Solutionmentioning

confidence: 99%

“…As pointed out by Saillenfest et al (2020), one must be careful about the normalisation used for λ. Here, we adopt R eq = 60268 km by convention and we renormalise each quantity in Eqs.…”

Section: Precession Constantmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The past and future obliquity of Saturn as Titan migrates

Saillenfest

Lari

Boué

et al. 2021

A&A

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Long-Term Evolution of the Saturnian System

Ćuk,

El Moutamid,

Lari

et al. 2024

Space Sci Rev

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Here we present the current state of knowledge on the long-term evolution of Saturn’s moon system due to tides within Saturn. First we provide some background on tidal evolution, orbital resonances and satellite tides. Then we address in detail some of the present and past orbital resonances between Saturn’s moons (including the Enceladus-Dione and Titan-Hyperion resonances) and what they can tell us about the evolution of the system. We also present the current state of knowledge on the spin-axis dynamics of Saturn: we discuss arguments for a (past or current) secular resonance of Saturn’s spin precession with planetary orbits, and explain the links of this resonance to the tidal evolution of Titan and a possible recent cataclysm in the Saturnian system. We also address how the moons’ orbital evolution, including resonances, affects the evolution of their interiors. Finally, we summarize the state of knowledge about the Saturnian system’s long-term evolution and discuss prospects for future progress.

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The large obliquity of Saturn explained by the fast migration of Titan

Saillenfest¹,

Lari²,

Boué³

2021

Nat Astron

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The obliquity of a planet is the tilt between its equator and its orbital plane. Giant planets are expected to form with near-zero obliquities [1,2]. After its formation, some dynamical mechanism must therefore have tilted Saturn up to its current obliquity of 26.7 • . This event is traditionally thought to have happened more than 4 Gyrs ago during the late planetary migration [3,4,5] because of the crossing of a resonance between the spin-axis precession of Saturn and the nodal orbital precession mode of Neptune [6]. Here, we show that the fast tidal migration of Titan measured by [7] is incompatible with this scenario, and that it offers a new explanation for Saturn's current obliquity. A significant migration of Titan would prevent any early resonance, invalidating previous constraints on the late planetary migration set by the tilting of Saturn [8,9,10]. We propose instead that the resonance was encountered recently, about 1 Gyr ago, forcing Saturn's obliquity to increase from a small value (possibly less than 3 • ), up to its current state. This scenario suggests that Saturn's normalised polar moment of inertia lies between 0.224 and 0.237. Our findings bring out a new paradigm for the spin-axis evolution of Saturn, Jupiter [11], and possibly giant exoplanets in multiple systems, whereby obliquities are not settled once for all, but continuously evolve as a result of the migration of their satellites.We investigate whether the spin-axis dynamics of Saturn could have been influenced by the migration of its satellites. The torque applied by the sun on Saturn's equatorial bulge produces a precession of its spin axis with a mean frequency ψ = α (1−e 2 ) −3/2 cos ε, where e is the eccentricity of Saturn, ε is its obliquity, and α is called its precession constant [12]. The value of α incorporates the extra torques produced by Saturn's satellites [1,13]. It also depends on Saturn's orbital and physical parameters, among which all are well known except Saturn's normalised polar moment of inertia λ. Estimates found in the literature broadly range in λ ∈ [0.200, 0.240] but they are model-dependent and a proper uncertainty range is hard to define (see Methods). Exploring this whole interval gives a current precession constant α 0 ranging from 0.747 to 0.894 /yr.We take into account the migration of Saturn's satellites by changing their contributions to α. The measurements of [7] unveiled a fast migration for Titan, and a similar tidal timescale t tide = a/ ȧ for all six satellites of Saturn studied. Both these findings support the "resonance locking" tidal 1

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The future large obliquity of Jupiter

Cited by 20 publications

References 64 publications

The past and future obliquity of Saturn as Titan migrates

The past and future obliquity of Saturn as Titan migrates

Long-Term Evolution of the Saturnian System

The large obliquity of Saturn explained by the fast migration of Titan

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