[專題演講] 【12月6日】Melaine Saillenfest / Coevolution of moons and the spin axis of their host planet

Astrometric observations of the moons of Jupiter and Saturn have revealed that their orbits expand over time faster than previously thought. This significant orbital “migration” implies that efficient mechanisms of tidal energy dissipation are at play in the interiors of gaseous planets. These findings profoundly affect our understanding of the formation and evolution of moons, but also of the spin-axis dynamics of their host planet. The coupling between the planet’s spin-axis dynamics (the “Cassini states”) and the moons’ orbital dynamics (the “Laplace plane”) can gradually tilt the planet and make the system converge to a highly unstable configuration. This mechanism has direct applications in the Solar system: Jupiter today is about to start the tilting phase, Saturn is probably halfway in, and Uranus may have completed the final unstable stage.

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