Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay

Abstract

Recent analyses have revealed a mystery. The orbital period of the highly inflated hot Jupiter, WASP-12b, is decreasing rapidly. The rate of inspiral, however, is too fast to be explained by either eccentricity tides or equilibrium stellar tides. While dynamical stellar tides are possible, they require a subgiant structure for the star, whereas stellar models point toward a main sequence host. Here, we show that these hitherto irreconcilable observations might be explained by planetary obliquity tides if planet b's spin vector is trapped in a high-obliquity state maintained by a secular spin-orbit resonance with an unseen exterior perturbing planet. We derive constraints on the obliquity ($\epsilon \gtrsim 50^{\circ }$), reduced tidal quality factor ($Q^{\prime }\sim 10^6-10^7$), and perturbing planet parameters ($M_2\sim 10-20M_{\oplus }$, $a_2\lesssim 0.04\mathrm{AU}$) required to generate the observed orbital decay. Direct N-body simulations that include tidal and spin dynamics reinforce the plausibility of the scenario. Furthermore, we show that the resonance could have been captured when planet b's obliquity was small, making the proposed sequence of events easy to explain. The hypothetical perturbing planet is within the limits of current radial velocity constraints on the system yet is also detectable. If it exists, it could provide evidence in favor of the in situ formation hypothesis for hot Jupiters.

arXiv commentpublished in ApJL, small error in Figure 4 corrected in this version

References in corpus (39)

• Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
• Tidal dissipation in stars and giant planets
• Tidal Decay of Close Planetary Orbits
• WASP-12b: The hottest transiting planet yet discovered
• Tidal dissipation in rotating giant planets
• The Equilibrium-Tide Model for Tidal Friction
• The GAPS Programme with HARPS-N@TNG XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets
• Friends of Hot Jupiters I: A Radial Velocity Search for Massive, Long-Period Companions to Close-In Gas Giant Planets
• Is tidal heating sufficient to explain bloated exoplanets? Consistent calculations accounting for finite initial eccentricity
• Orbital perturbations on transiting planets: A possible method to measure stellar quadrupoles and to detect Earth-mass planets
• WASP-47: A Hot Jupiter System with Two Additional Planets Discovered by K2
• In Situ Formation and Dynamical Evolution of Hot Jupiter Systems
• Near-UV Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system
• Probing the Interiors of Very Hot Jupiters Using Transit Light Curves
• Thermal Phase Variations of WASP-12b: Defying Predictions
• The Apparently Decaying Orbit of WASP-12
• Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b
• On the Orbit of Exoplanet WASP-12b
• Obliquity Tides on Hot Jupiters
• Inflating and Deflating Hot Jupiters: Coupled Tidal and Thermal Evolution of Known Transiting Planets
• Cassini States with Dissipation: Why Obliquity Tides Cannot Inflate Hot Jupiters
• Tidal dissipation within hot Jupiters: a new appraisal
• Near-infrared Thermal Emission from WASP-12b: detections of the secondary eclipse in Ks, H & J
• Empirical Tidal Dissipation in Exoplanet Hosts From Tidal Spin-Up
• The Transit Light Curve project. XIV. Confirmation of Anomalous Radii for the Exoplanets TrES-4b, HAT-P-3b, and WASP-12b
• Transit Timing Variation Measurements of WASP-12b and Qatar-1b: No Evidence for Additional Planets
• Hierarchical Bayesian calibration of tidal orbit decay rates among hot Jupiters
• Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier
• Tidal Dissipation in WASP-12
• Orbital period variations of hot-Jupiters caused by the Applegate effect
• Understanding WASP-12b
• A New Model of Roche-lobe Overflow for Short-Period Gaseous Planets and Binary Stars
• Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin
• Explorations into the Viability of Coupled Radius-Orbit Evolutionary Models for Inflated Planets
• Orbital eccentricity of WASP-12 and WASP-14 from new radial-velocity monitoring with SOPHIE
• A Secular Resonant Origin for the Loneliness of Hot Jupiters
• Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates
• On the Detection of Non-Transiting Hot Jupiters in Multiple-Planet Systems
• Reassessing Exoplanet Light Curves with a Thermal Model

Cited by in corpus (32)

• Stellar obliquities in exoplanetary systems
• The Orbit of WASP-12b is Decaying
• WASP-4b Arrived Early for the TESS Mission
• Mass Loss from the Exoplanet WASP-12b Inferred from $\text{Spitzer}$ Phase Curves
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• TraMoS V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab
• Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion
• TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability
• The Possible Tidal Demise of Kepler's First Planetary System
• Excitation of Planetary Obliquities Through Planet-Disk Interactions
• Tidal erasure of stellar obliquities constrains the timing of hot Jupiter formation
• Planets Across Space and Time (PAST). V. The evolution of hot Jupiters revealed by the age distribution of their host stars
• 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
• Atmospheres on Nonsynchronized Eccentric-tilted Exoplanets I: Dynamical Regimes
• Formation of hot Jupiters through disk migration and evolving stellar tides
• The future large obliquity of Jupiter
• Non-Trivial Oblique Spin Equilibria of Super-Earths in Multi-planetary Systems
• Signatures of Obliquity in Thermal Phase Curves of Hot Jupiters
• TASTE V. A new ground-based investigation of orbital decay in the ultra-hot Jupiter WASP-12b
• Measuring Tidal Dissipation in Giant Planets from Tidal Circularization
• TESS Timings of 31 Hot Jupiters with Ephemeris Uncertainties
• Tentative Evidence for Transit Timing Variations of WASP-161b
• PEPSI's non-detection of escaping hydrogen and metal lines adds to the enigma of WASP-12 b
• TrES-1 b: A Case Study in Detecting Secular Evolution of Exoplanet Orbits
• Quantification of Tides in Giant Planets from Observations
• How to measure tidal dissipation in long resonant chains
• The Coupled Tidal Evolution of the Moons and Spins of Warm Exoplanets
• The tidal quality of the hot Jupiter WASP-12b
• The Influence of General Relativity on the Spins of Celestial Bodies in Inclined Orbits
• Characterizing the WASP-4 system with TESS and radial velocity data: Constraints on the cause of the hot Jupiter's changing orbit and evidence of an outer planet
• Three-dimensional transport-induced chemistry on temperate sub-Neptune K2-18b, Part II: the combined effects of atmospheric dynamics and chemical reactions