Tidally-Induced Radius Inflation of Sub-Neptunes

Abstract

Recent work suggests that many short-period super-Earth and sub-Neptune planets may have significant spin axis tilts ("obliquities"). When planets are locked in high-obliquity states, the tidal dissipation rate may increase by several orders of magnitude. This intensified heat deposition within the planets' interiors should generate significant structural consequences, including atmospheric inflation leading to larger transit radii. Using up-to-date radius estimates from Gaia Data Release 2, we show evidence for $\sim 50\%$ larger average radii of planets wide of first-order mean-motion resonances, a population of planets with a theorized frequent occurrence of high obliquities. We investigate whether this radius trend could be a signature of obliquity tides. Using an adaptation of the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution toolkit, we model the atmospheric evolution of sub-Neptune-mass planets in response to additional internal heat from obliquity tides. The degree of radius inflation predicted by the models is $\sim 10\%-100\%$ for tidal luminosities $\gtrsim 10^{-5}$ of the incident stellar power; this degree of inflation is broadly consistent with the observations and can approximately be described by power law relationships. We present a few case studies of very low density "super-puff" planets -- Kepler-79 d, Kepler-31 c, and Kepler-27 b -- and show that they are strong candidates for potentially having undergone tidally-induced radius inflation. We also discuss how the discrepancy between the two populations of planets with masses derived from radial velocities and transit timing variations is connected to the radius distribution features we have identified. Altogether, the calculations in this work confirm that tidal dissipation has non-negligible consequences for the structural properties of short-period sub-Neptunes.

17 pages, 11 figures, accepted to ApJ

References in corpus (30)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Transiting Exoplanet Survey Satellite
• DHP Framework: Digital Health Passports Using Blockchain -- Use case on international tourism during the COVID-19 pandemic
• Most 1.6 Earth-Radius Planets are not Rocky
• Atmospheric Escape from Hot Jupiters
• On the radiative equilibrium of irradiated planetary atmospheres
• Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited
• Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
• Tidal Locking of Habitable Exoplanets
• Resonant Repulsion of Kepler Planet Pairs
• Tidal Heating of Extra-Solar Planets
• Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius
• Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
• Inflating and Deflating Hot Jupiters: Coupled Tidal and Thermal Evolution of Known Transiting Planets
• The period ratio distribution of Kepler's candidate multiplanet systems
• Tidal dissipation within hot Jupiters: a new appraisal
• Obliquity-Driven Sculpting of Exoplanetary Systems
• Deformation and tidal evolution of close-in planets and satellites using a Maxwell viscoelastic rheology
• Coupled Evolution with Tides of the Radius and Orbit of Transiting Giant Planets: General Results
• Tidal dissipation and the formation of Kepler near-resonant planets
• CKS VIII: Eccentricities of Kepler Planets and Tentative Evidence of a High Metallicity Preference for Small Eccentric Planets
• Dusty outflows in planetary atmospheres: Understanding "super-puffs" and transmission spectra of sub-Neptunes
• From Hot Jupiters to Super-Earths via Roche Lobe Overflow
• Hot-Jupiter Inflation due to Deep Energy Deposition
• Complete spin and orbital evolution of close-in bodies using a Maxwell viscoelastic rheology
• Ohmic Dissipation in Mini-Neptunes
• Do planets remember how they formed?
• Tidal Heating of Young Super-Earth Atmospheres

Cited by in corpus (40)

• The Featureless Transmission Spectra of Two Super-Puff Planets
• A High Internal Heat Flux and Large Core in a Warm Neptune Exoplanet
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• A warm Neptune's methane reveals core mass and vigorous atmospheric mixing
• The Warm Neptune GJ 3470b has a Polar Orbit
• Deflating Super-Puffs: Impact of Photochemical Hazes on the Observed Mass-Radius Relationship of Low Mass Planets
• TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain
• Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway
• Architectures of Compact Super-Earth Systems Shaped by Instabilities
• Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion
• TESS-Keck Survey IX: Masses of Three Sub-Neptunes Orbiting HD 191939 and the Discovery of a Warm Jovian Plus a Distant Sub-Stellar Companion
• The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System
• Are WASP-107-like Systems Consistent with High-eccentricity Migration?
• HD 28109 hosts a trio of transiting Neptunian planets including a near-resonant pair, confirmed by ASTEP from Antarctica
• Dynamics and Origins of the Near-Resonant Kepler Planets
• CKS IX: Revisiting the Minimum-Mass Extrasolar Nebula with Precise Stellar Parameters
• Resonant sub-Neptunes are puffier
• A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings
• A Tidal Origin for a 3-body Resonance in Kepler-221
• The effects of nonlinearities on tidal flows in the convective envelopes of rotating stars and planets in exoplanetary systems
• Oblique rings from migrating exomoons: A possible origin for long-period exoplanets with enlarged radii
• GJ 229B: Solving the Puzzle of the First Known T-Dwarf with the APOLLO Retrieval Code
• Thermal Phase Curves of XO-3b: an Eccentric Hot Jupiter at the Deuterium Burning Limit
• K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System
• Planet Hunters TESS III: two transiting planets around the bright G dwarf HD 152843
• Star-Planet Interactions: A Computational View
• A close-in puffy Neptune with hidden friends: The enigma of TOI 620
• Warm Jupiters Beyond the Tidal Synchronization Limit May Exhibit a Wide Range of Secondary Eclipse Depths
• The phase curve of the ultra-hot Jupiter WASP-167b as seen by TESS
• An extremely low-density exoplanet spins slow
• Plausibility of Capture into High-Obliquity States for Exoplanets in the M Dwarf Habitable Zone
• Exploring Exoplanet Dynamics with JWST: Tides, Rotation, Rings, and Moons
• Patchy nightside clouds on ultra-hot Jupiters: General Circulation Model simulations with radiatively active cloud tracers
• Variations in the Radius Distribution of Single- and Compact Multiple-transiting Planets
• TOI-3757 b: A low density gas giant orbiting a solar-metallicity M dwarf
• Do Outer Giants Inflate Neptune-sized Planets? An Architecture-Dependent Mass-Radius Relation
• Refining the Masses and Radii of the Star Kepler-33 and its Five Transiting Planets
• Split Peas in a Pod: Intra-System Uniformity of Super-Earths and Sub-Neptunes
• A Multi-Planet System's Sole Super-Puff: Exploring Allowable Physical Parameters for the Cold Super-Puff HIP 41378 f
• Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs