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arXiv · 2604.13200

Are Thalassa and Despina in Resonance Lock with Neptune's Oscillations?

Matija Ćuk·Harrison F. Agrusa·Marina Brozović·Matthew M. Hedman
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Abstract

The two innermost moons of Neptune, Naiad and Thalassa, are currently in a 73:69 mean-motion resonance. This resonance relies on the large inclination of Naiad, and we estimate that Naiad requires multiple Gyr to reach its $4.7^{\circ}$ inclination through this resonance. However, we find through direct numerical simulations that the current Naiad-Thalassa resonance is unstable on Myr timescales due to perturbations from the neighboring moon Despina. As this instability is a product of convergent tidal evolution predicted by equilibrium tidal theory, we propose that the innermost moons of Neptune may migrate through resonant-lock tides. If both Despina and Thalassa are locked to two resonant oscillations modes within Neptune, the frequencies of which evolve approximately in parallel, Naiad-Thalassa resonance can be stable for much longer. We find that Lindblad resonances with low-order $l=m=1$, $n=1$ g-modes at Neptune may be suitable candidates for driving the resonant-lock evolution of Thalassa and Despina, and possibly even Galatea.

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Matija Ćuk, Harrison F. Agrusa, Marina Brozović, Matthew M. Hedman. 2026-04-14. Are Thalassa and Despina in Resonance Lock with Neptune's Oscillations?. https://arxiv.org/abs/2604.13200

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