The Coupled Tidal Evolution of the Moons and Spins of Warm Exoplanets

Abstract

Context: The Solar System giant planets harbour a wide variety of moons. Moons around exoplanets are plausibly similarly abundant, even though most of them are likely too small to be easily detectable with modern instruments. Moons are known to affect the long-term dynamics of the spin of their host planets; however, their influence on warm exoplanets (i.e.\ with moderately short periods of about $10$ to $200$~days), which undergo significant star-planet tidal dissipation, is still unclear. Aims: Here, we study the coupled dynamical evolution of exomoons and the spin dynamics of their host planets, focusing on warm exoplanets. Methods: Analytical criteria give the relevant dynamical regimes at play as a function of the system's parameters. Possible evolution tracks mostly depend on the hierarchy of timescales between the star-planet and the moon-planet tidal dissipations. We illustrate the variety of possible trajectories using self-consistent numerical simulations. Results: We find two principal results: i) Due to star-planet tidal dissipation, a substantial fraction of warm exoplanets naturally evolve through a phase of instability for the moon's orbit (the `Laplace plane' instability). Many warm exoplanets may have lost their moon(s) through this process. ii) Surviving moons slowly migrate inwards due to the moon-planet tidal dissipation until they are disrupted below the Roche limit. During their last migration stage, moons -- even small ones -- eject planets from their tidal spin equilibrium. Conclusions: The loss of moons through the Laplace plane instability may contribute to disfavour the detection of moons around close-in exoplanets. Moreover, moons (even those that have been lost) play a critical role in the final obliquities of warm exoplanets. Hence, the existence of exomoons poses a serious challenge in predicting the present-day obliquities of observed exoplanets.

19 pages, 12 figures, Accepted to A&A. Abstract abridged for arXiv. Comments welcome!

References in corpus (35)

• Transit timing effects due to an exomoon
• Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
• Satellite dynamics on the Laplace surface
• Resonance locking in giant planets indicated by the rapid orbital expansion of Titan
• Tidal evolution of hierarchical and inclined systems
• Tidal dissipation within hot Jupiters: a new appraisal
• A secondary atmosphere on the rocky exoplanet 55 Cancri e
• Obliquity-Driven Sculpting of Exoplanetary Systems
• An Exomoon Survey of 70 Cool Giant Exoplanets and the New Candidate Kepler-1708 b-i
• Predicting Photometric and Spectroscopic Signatures of Rings around Transiting Extrasolar Planets
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object
• Complete spin and orbital evolution of close-in bodies using a Maxwell viscoelastic rheology
• Excitation of Planetary Obliquities Through Planet-Disk Interactions
• Peering into the Young Planetary System AB Pic. Atmosphere, Orbit, Obliquity & Second Planetary Candidate
• Secular spin-axis dynamics of exoplanets
• Self-Consistent Spin, Tidal and Dynamical Equations of Motion in the REBOUNDx Framework
• The large obliquity of Saturn explained by the fast migration of Titan
• Dynamics of Colombo's Top: Tidal Dissipation and Resonance Capture, With Applications to Oblique Super-Earths, Ultra-Short-Period Planets and Inspiraling Hot Jupiters
• The future large obliquity of Jupiter
• Tilting Uranus via the migration of an ancient satellite
• A Simplified Photodynamical Model for Planetary Mass Determination in Low-Eccentricity Multi-Transiting Systems
• Non-Trivial Oblique Spin Equilibria of Super-Earths in Multi-planetary Systems
• Oblique rings from migrating exomoons: A possible origin for long-period exoplanets with enlarged radii
• Leaning Sideways: VHS 1256-1257 b is a Super-Jupiter with a Uranus-like Obliquity
• The past and future obliquity of Saturn as Titan migrates
• Tidal excitation of the obliquity of Earth-like planets in the habitable zone of M-dwarf stars
• The ominous fate of exomoons around hot Jupiters in the high-eccentricity migration scenario
• Pathways of Survival of Exomoons and Inner Exoplanets
• Detecting Planetary Oblateness in the Era of JWST: A Case Study of Kepler-167e
• Future destabilisation of Titan as a result of Saturn's tilting
• Eviction-like resonances for satellite orbits. Application to Phobos, the main satellite of Mars
• Plausibility of Capture into High-Obliquity States for Exoplanets in the M Dwarf Habitable Zone
• Survival of satellites during the migration of a Hot Jupiter
• Initial conditions for tidal synchronisation of a planet by its moon