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.

arXiv comment19 pages, 12 figures, Accepted to A&A. Abstract abridged for arXiv. Comments welcome!

References in corpus (58)

• Breaking the Chains: Hot Super-Earth systems from migration and disruption of compact resonant chains
• Transit timing effects due to an exomoon
• Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
• Stability of Satellites Around Close-in Extrasolar Giant Planets
• Resonance locking as the source of rapid tidal migration in the Jupiter and Saturn moon systems
• Satellite dynamics on the Laplace surface
• Tidal Dissipation in Planet-Hosting Stars: Damping of Spin-Orbit Misalignment and Survival of Hot Jupiters
• The Physics of Bodily Tides in Terrestrial Planets, and the Appropriate Scales of Dynamical Evolution
• Evidence for a Large Exomoon Orbiting Kepler-1625b
• Resonance locking in giant planets indicated by the rapid orbital expansion of Titan
• Tidal evolution of hierarchical and inclined systems
• Cassini States with Dissipation: Why Obliquity Tides Cannot Inflate Hot Jupiters
• Tidal dissipation within hot Jupiters: a new appraisal
• A secondary atmosphere on the rocky exoplanet 55 Cancri e
• NOTE: Explaining why the Uranian satellites have equatorial prograde orbits despite the large planetary obliquity
• On the Terminal Rotation Rates of Giant Planets
• KOI-152's Low Density Planets
• Obliquity-Driven Sculpting of Exoplanetary Systems
• Tidal synchronization of close-in satellites and exoplanets. A rheophysical approach
• 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
• Outcomes and Duration of Tidal Evolution in a Star-Planet-Moon System
• Climate instability on tidally locked exoplanets
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• A collisionless scenario for Uranus tilting
• Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object
• Obliquity Constraints on an Extrasolar Planetary-Mass Companion
• 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
• Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay
• Secular spin-axis dynamics of exoplanets
• Giant Planet Scatterings and Collisions: Hydrodynamics, Merger-Ejection Branching Ratio, and Properties of the Remnants
• Self-Consistent Spin, Tidal and Dynamical Equations of Motion in the REBOUNDx Framework
• Tilting Ice Giants with a Spin-Orbit Resonance
• The large obliquity of Saturn explained by the fast migration of Titan
• Dynamics of Colombo's Top: Generating Exoplanet Obliquities from Planet-Disk Interactions
• 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 thermal phase curve offset on tidally- and non-tidally-locked exoplanets: A shallow water model
• The future large obliquity of Jupiter
• A Simplified Photodynamical Model for Planetary Mass Determination in Low-Eccentricity Multi-Transiting Systems
• Tilting Uranus via the migration of an ancient satellite
• Non-Trivial Oblique Spin Equilibria of Super-Earths in Multi-planetary Systems
• 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
• Oblique rings from migrating exomoons: A possible origin for long-period exoplanets with enlarged radii
• 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
• Cassini states of a rigid body with a liquid core
• Triaxial Deformation and Asynchronous Rotation of Rocky Planets in the Habitable Zone of Low-Mass Stars
• Tidal friction in satellites and planets. The new version of the creep tide theory
• 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