Why do warm Neptunes present nonzero eccentricity?

Abstract

Most Neptune-mass planets in close-in orbits (orbital periods less than a few days) present nonzero eccentricity, typically around 0.15. This is somehow unexpected, as these planets undergo strong tidal dissipation that should circularize their orbits in a time-scale shorter than the age of the system. In this paper we discuss some mechanisms that can oppose to bodily tides, namely, thermal atmospheric tides, evaporation of the atmosphere, and excitation from a distant companion. In the first two cases, the eccentricity can increase consistently, while in the last one, the eccentricity can only be excited for a limited amount of time (that may nevertheless exceed the age of the system). We show the limitations of these different mechanisms and how some of them could, depending on specific properties of the observed planetary systems, account for their presently observed eccentricities.

8 pages, 2 figures

References in corpus (43)

• Shrinking binary and planetary orbits by Kozai cycles with tidal friction
• The evaporation valley in the Kepler planets
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• Planet Migration and Binary Companions: the case of HD 80606b
• Atmospheric Circulation and Tides of "51Peg b-like" Planets
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Evidence for a Distant Giant Planet in the Solar System
• Equatorial superrotation on tidally locked exoplanets
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• A diagram for the evaporation status of extrasolar planets
• Multiple-Planet Scattering and the Origin of Hot Jupiters
• Photoevaporation and High-Eccentricity Migration Created the Sub-Jovian Desert
• A short-period censor of sub-Jupiter mass exoplanets with low density
• Tidally Heated Terrestrial Exoplanets: Viscoelastic Response Models
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars
• Simulating the escaping atmospheres of hot gas planets in the solar neighborhood
• Formation and Stellar Spin-Orbit Misalignment of Hot Jupiters from Lidov-Kozai Oscillations in Stellar Binaries
• An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ436 b
• Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star
• Bodily tides near spin-orbit resonances
• HAT-P-26b: A Low-Density Neptune-Mass Planet Transiting a K Star
• A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
• The long egress of GJ~436b's giant exosphere
• Tidal evolution of hierarchical and inclined systems
• Deformation and tidal evolution of close-in planets and satellites using a Maxwell viscoelastic rheology
• The HARPS search for southern extra-solar planets. XVII. Super-Earth and Neptune-mass planets in multiple planet systems HD47186 and HD181433
• Anelastic tidal dissipation in multi-layer planets
• HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities
• The ELODIE survey for northern extra-solar planets IV. HD196885, a close binary star with a 3.7-year planet
• Evidence for a lost population of close-in exoplanets
• A new Neptune-mass planet orbiting HD 219828
• Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits
• The Hubble PanCET program: An extensive search for metallic ions in the exosphere of GJ 436 b
• Atmospheric tides in Earth-like planets
• Pumping the eccentricity of exoplanets by tidal effect
• Dynamical evolution of the Gliese 436 planetary system - Kozai migration as a potential source for Gliese 436b's eccentricity
• Torque on an exoplanet from an anisotropic evaporative wind
• Spin evolution of Earth-sized exoplanets, including atmospheric tides and core-mantle friction
• On the Stability of Extrasolar Planetary Systems and other Closely Orbiting Pairs
• Orbital migration induced by anisotropic evaporation. Can hot Jupiters form hot Neptunes ?
• Tidal damping of the mutual inclination in hierachical systems
• Spin-driven tidal pumping: Tidally driven changes in planetary spin coupled with secular interactions between planets

Cited by in corpus (38)

• The Warm Neptune GJ 3470b has a Polar Orbit
• DREAM I. Orbital architecture orrery
• A disk-driven resonance as the origin of high inclinations of close-in planets
• A new perspective on interiors of ice-rich planets: Ice-rock mixture instead of ice on top of rock
• Mapping the exo-Neptunian landscape. A ridge between the desert and savanna
• The JADE code: Coupling secular exoplanetary dynamics and photo-evaporation
• The polar orbit of the warm Neptune GJ436b seen with VLT/ESPRESSO
• TOI-674b: an oasis in the desert of exo-Neptunes transiting a nearby M dwarf
• The GAPS Programme at TNG XXVIII -- A pair of hot-Neptunes orbiting the young star TOI-942
• TOI-269 b: An eccentric sub-Neptune transiting a M2 dwarf revisited with ExTrA
• TOI-5005 b: A super-Neptune in the savanna near the ridge
• TOI-1728b: The Habitable-zone Planet Finder confirms a warm super Neptune orbiting an M dwarf host
• HATS-38 b and WASP-139 b join a growing group of hot Neptunes on polar orbits
• 10,000 Resolved Triples from Gaia: Empirical Constraints on Triple Star Populations
• Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant
• The young mini-Neptune HD 207496b that is either a naked core or on the verge of becoming one
• TOI-179: a young system with a transiting compact Neptune-mass planet and a low-mass companion in outer orbit
• Three super-Earths and a possible water world from TESS and ESPRESSO
• The TESS-Keck Survey. VI. Two Eccentric sub-Neptunes Orbiting HIP-97166
• TOI-4438 b: a transiting mini-Neptune amenable to atmospheric characterization
• Planetary companions orbiting the M dwarfs GJ 724 and GJ 3988. A CARMENES and IRD collaboration
• The GAPS Programme at TNG -- XXIV. An eccentric Neptune-mass planet near the inner edge of the BD-11 4672 habitable zone
• ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system
• TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS and SOPHIE
• An analytical model for tidal evolution in co-orbital systems I. Application to exoplanets
• The TESS-Keck Survey. XIII. An Eccentric Hot Neptune with a Similar-Mass Outer Companion around TOI-1272
• The Hot-Neptune Initiative (HONEI) I. Two hot sub-Neptunes on a close-in, eccentric orbit (TOI-5800 b) and a farther-out, circular orbit (TOI-5817 b)
• NIRPS detection of delayed atmospheric escape from the warm and misaligned Saturn-mass exoplanet WASP-69b
• Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
• The K2-24 planetary system revisited by CHEOPS
• The Neptunian ridge as a natural outcome of high-eccentricity tidal migration
• Three young planets around the K-dwarf K2-198: High-energy environment, evaporation history and expected future
• The Dynamical History of the Kepler-221 Planet System
• Confirmation of the hot super-Neptune TOI-672 b with NIRPS and HARPS and Insights into the Neptunian desert around M dwarfs
• Discovery of a transiting hot water-world candidate orbiting Ross 176 with TESS and CARMENES
• Super-earths and mini-neptunes follow different orbital period-eccentricity relations
• A Homogeneous Catalog of Rossiter-McLaughlin Systems: Distinct $e$-$\lambda$ Trends in Three Gas-Giant Mass Regimes
• The orbital architecture and stability of the $\mu$ Arae planetary system