Evidence of a gap in the envelope mass fraction of sub-Saturns

Abstract

Under the core-accretion model, gas giants form via runaway accretion. This process starts when the mass of the accreted envelope becomes equal to the mass of the core. Here, we model a population of warm sub-Saturns to search for imprints of their formation history in their internal structure. Using the GAS gianT modeL for Interiors (GASTLI), we calculate a grid of interior structure models on which we perform retrievals for our sample of 28 sub-Saturns to derive their envelope mass fractions ($f_{env}$). For each planet, we run three different retrievals assuming low (-2.0 < log(Fe/H) < 0.5), medium ( 0.5 < log(Fe/H) < 1.4), and high (1.4 < log(Fe/H) < 1.7) atmospheric metallicity. The distribution of $f_{env}$ in our sample is then compared to predictions of planet formation models. When compared to the outcomes of a planetesimal accretion model, we find that we require medium to high atmospheric metallicities to reproduce the simulated planet population. Additionally, we find a bimodal distribution of $f_{env}$ in our sample with a gap that is located at different values of $f_{env}$ for different atmospheric metallicities. For the high atmospheric metallicity case, the gap in the $f_{env}$ distribution is located between 0.5 and 0.7, which is consistent with assumptions by the core-accretion model where runaway accretion starts when $M_{env}\approx M_{core}$ ($f_{env}\sim 0.5$). We also find a bimodal distribution of the hydrogen and helium mass fraction ($f_{H/He}$) with a gap at $f_{H/He}=0.3$. The location of this gap is independent of the assumed atmospheric metallicity. Lastly, we compare the distributions of our sub-Saturns in the Neptunian savanna to a population of sub-Saturns in the Neptune desert and ridge. We find that the observed $f_{env}$ distribution of savanna and ridge sub-Saturns is consistent with the planets coming from the same underlying population.

arXiv comment12 pages, 9 figures, accepted for publication in A&A

References in corpus (89)

• emcee: The MCMC Hammer
• The Revised TESS Input Catalog and Candidate Target List
• Towards a Deterministic Model of Planetary Formation I: a Desert in the Mass and Semi Major Axis Distributions of Extra Solar Planets
• The evaporation valley in the Kepler planets
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• Extrasolar planet population synthesis I: Method, formation tracks and mass-distance distribution
• The Mass-Metallicity Relation for Giant Planets
• A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
• HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• Can we constrain interior structure of rocky exoplanets from mass and radius measurements?
• The nature of the TRAPPIST-1 exoplanets
• Super-Earth Atmospheres: Self-Consistent Gas Accretion and Retention
• Atmospheric Escape and the Evolution of Close-in Exoplanets
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Hot super-Earths stripped by their host stars
• A diagram for the evaporation status of extrasolar planets
• Transit Timing Observations from Kepler: IV. Confirmation of 4 Multiple Planet Systems by Simple Physical Models
• A Study of the Shortest-Period Planets Found With Kepler
• Photoevaporation and High-Eccentricity Migration Created the Sub-Jovian Desert
• The coronal X-ray - age relation and its implications for the evaporation of exoplanets
• To Cool is to Accrete: Analytic Scalings for Nebular Accretion of Planetary Atmospheres
• Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio
• Mass-Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H${}_2$O, Na, and K
• Evolutionary Analysis of Gaseous Sub-Neptune-Mass Planets with MESA
• A short-period censor of sub-Jupiter mass exoplanets with low density
• Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
• Statistical properties of exoplanets. I. The period distribution: constraints for the migration scenario
• Emerging Trends in a Period-Radius Distribution of Close-in Planets
• The Complete transmission spectrum of WASP-39b with a precise water constraint
• HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf
• Planet formation with envelope enrichment: new insights on planetary diversity
• The TESS-HERMES survey Data Release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone
• Gas Giant Formation with Small Cores Triggered by Envelope Pollution by Icy Planetesimals
• The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age
• The formation of Jupiter by hybrid pebble-planetesimal accretion
• How cores grow by pebble accretion I. Direct core growth
• On the origin of the sub-Jovian desert in the orbital-period--planetary-mass plane
• Mass-Loss Evolution of Close-In Exoplanets: Evaporation of Hot Jupiters and the Effect on Population
• Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes
• Jupiter's formation and its primordial internal structure
• The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation
• Giant Planets
• DREAM I. Orbital architecture orrery
• Diffuser-Assisted Infrared Transit Photometry for Four Dynamically Interacting \textit{Kepler} Systems
• Spectral Properties of Cool Stars: Extended Abundance Analysis of Kepler Objects of Interest
• Characterisation of the hydrospheres of TRAPPIST-1 planets
• A New Model of Roche-lobe Overflow for Short-Period Gaseous Planets and Binary Stars
• Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion
• Jupiter's heavy-element enrichment expected from formation models
• The Metal-Rich Atmosphere of the Neptune HAT-P-26b
• HARPS-N radial velocities confirm the low densities of the Kepler-9 planets
• The TESS-Keck Survey XX: 15 New TESS Planets and a Uniform RV Analysis of all Survey Targets
• Mapping the exo-Neptunian landscape. A ridge between the desert and savanna
• The maximum mass of planetary embryos formed in core-accretion models
• NGTS-11 b / TOI-1847 b: A transiting warm Saturn recovered from a TESS single-transit event
• Dynamics and Formation of the Near-Resonant K2-24 System: Insights from Transit-Timing Variations and Radial Velocities
• On the mass of gas giant planets: Is Saturn a failed gas giant?
• The TESS-Keck Survey I: A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras
• Two Transiting Low Density Sub-Saturns from K2
• TOI-216b and TOI-216c: Two warm, large exoplanets in or slightly wide of the 2:1 orbital resonance
• TOI-5005 b: A super-Neptune in the savanna near the ridge
• TOI-2525 b and c: A pair of massive warm giant planets with a strong transit timing variations revealed by TESS
• SOPHIE velocimetry of Kepler transit candidates XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system
• Composition of giant planets: the roles of pebbles and planetesimals
• Towards a new era in giant exoplanet characterisation
• Kepler-539: a young extrasolar system with two giant planets on wide orbits and in gravitational interaction
• TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
• Evidence of a Sub-Saturn around EPIC~211945201
• K2-19b and c are in a 3:2 Commensurability but out of Resonance: A Challenge to Planet Assembly by Convergent Migration
• GASTLI: An open-source coupled interior-atmosphere model to unveil gas giant composition
• Kepler-1656b: a Dense Sub-Saturn With an Extreme Eccentricity
• K2-139 b: a low-mass warm Jupiter on a 29-day orbit transiting an active K0 V star
• The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars
• Physics of Planet Trapping with Applications to HL Tau
• TOI-4010: A System of Three Large Short-Period Planets With a Massive Long-Period Companion
• A Simplified Photodynamical Model for Planetary Mass Determination in Low-Eccentricity Multi-Transiting Systems
• TESS Observations of Kepler systems with Transit Timing Variations
• A warm super-Neptune around the G-dwarf star TOI-1710 revealed with TESS, SOPHIE and HARPS-N
• Formation of Planetary Populations II: Effects of Initial Disk Size & Radial Dust Drift
• The GAPS programme at TNG XLIV. Projected rotational velocities of 273 exoplanet-host stars observed with HARPS-N
• Using HARPS-N to characterise the long-period planets in the PH-2 and Kepler-103 systems
• VaTEST I: Validation of Sub-Saturn Exoplanet TOI-181b in Narrow Orbit from its Host Star
• Three Warm Jupiters orbiting TOI-6628, TOI-3837, TOI-5027 and one sub-Saturn orbiting TOI-2328
• A hot mini-Neptune and a temperate, highly eccentric sub-Saturn around the bright K-dwarf TOI-2134
• TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS and SOPHIE
• K2-280b -- a low density warm sub-Saturn around a mildly evolved star
• The K2-24 planetary system revisited by CHEOPS
• The TESS-Keck Survey. XIX. A Warm Transiting Sub-Saturn Mass Planet and a non-Transiting Saturn Mass Planet Orbiting a Solar Analog