The formation of mini-Neptunes
arXiv:1709.04736 · doi:10.3847/1538-4357/aa8cd0
Abstract
Mini-Neptunes seem to be common planets. In this work we investigate the possible formation histories and predicted occurrence rates of mini-Neptunes assuming the planets form beyond the iceline. We consider pebble and planetesimal accretion accounting for envelope enrichment and two different opacity conditions. We find that the formation of mini-Neptunes is a relatively frequent output when envelope enrichment by volatiles is included, and that there is a "sweet spot" for mini-Neptune formation with a relatively low solid accretion rate of ~10^{-6} Earth masses per year. This rate is typical for low/intermediate-mass protoplanetary disks and/or disks with low metallicities. With pebble accretion, envelope enrichment and high opacity favor the formation of mini-Neptunes, with more efficient formation at large semi-major axes (~30 AU) and low disk viscosity. For planetesimal accretion, such planets can form also without enrichment, with the opacity being a key aspect in the growth history and favorable formation location. Finally, we show that the formation of Neptune-like planets remains a challenge for planet formation theories.
arXiv commentAccepted for publication in ApJ
References in corpus (45)
- The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
- Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
- Rapid growth of gas-giant cores by pebble accretion
- A simple model for the evolution of the dust population in protoplanetary disks
- Most 1.6 Earth-Radius Planets are not Rocky
- Models of Giant Planet formation with migration and disc evolution
- A Closely-Packed System of Low-Mass, Low-Density Planets Transiting Kepler-11
- The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks
- The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
- Forming the cores of giant planets from the radial pebble flux in protoplanetary discs
- Separating gas-giant and ice-giant planets by halting pebble accretion
- Protoplanetary Disk Structures in Ophiuchus II: Extension to Fainter Sources
- How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
- Gaseous Mean Opacities for Giant Planet and Ultracool Dwarf Atmospheres over a Range of Metallicities and Temperatures
- Planet Formation by Coagulation: A Focus on Uranus and Neptune
- Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
- Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations
- Formation and Structure of Low Density Exo-Neptunes
- The great dichotomy of the Solar System: small terrestrial embryos and massive giant planet cores
- Interior Models of Uranus and Neptune
- Composition and fate of short-period super-Earths: The case of CoRoT-7b
- The Mass of Kepler-93b and The Composition of Terrestrial Planets
- New indication for a dichotomy in the interior structure of Uranus and Neptune from the application of modified shape and rotation data
- Close-in planetesimal formation by pile-up of drifting pebbles
- A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
- In-situ Accretion of Hydrogen-Rich Atmospheres on Short-Period Super-Earths: Implications for the Kepler-11 Planets
- Formation of Jupiter using opacities based on detailed grain physics
- Hydrodynamics of Embedded Planets' First Atmospheres. II. A Rapid Recycling of Atmospheric Gas
- The Formation of Super-Earths and Mini-Neptunes with Giant Impacts
- Planet formation with envelope enrichment: new insights on planetary diversity
- Planet formation models: the interplay with the planetesimal disc
- Gas Giant Formation with Small Cores Triggered by Envelope Pollution by Icy Planetesimals
- An Atmospheric Structure Equation for Grain Growth
- Grain opacity and the bulk composition of extrasolar planets. II. An analytical model for the grain opacity in protoplanetary atmospheres
- Short dissipation times of proto-planetary discs - an artifact of selection effects?
- Critical core mass for enriched envelopes: the role of H2O condensation
- The opacity of grains in protoplanetary atmospheres
- Jupiter's formation and its primordial internal structure
- Accretion of Uranus and Neptune from inward-migrating planetary embryos blocked by Jupiter and Saturn
- A new condition for the transition from runaway to oligarchic growth
- Accretion and Evolution of ~2.5 Earth-mass Planets with Voluminous H/He Envelopes
- The Formation of Uranus & Neptune: Challenges and Implications For Intermediate-Mass Exoplanets
- Simultaneous formation of Solar System giant planets
- The role of planetesimal fragmentation on giant planet formation
- Saving super-Earths: Interplay between pebble accretion and type I migration
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- Mass determinations of the three mini-Neptunes transiting TOI-125
- Giant planet formation models with a self-consistent treatment of the heavy elements
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- Using Deep Neural Networks to compute the mass of forming planets
- A new metric to quantify the similarity between planetary systems - application to dimensionality reduction using T-SNE
- Ariel Planetary Interiors White Paper
- GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation
- Sublimation of refractory minerals in the gas envelopes of accreting rocky planets
- Photosynthesis on Exoplanets and Exomoons from Reflected Light
- Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-Poor K Dwarf
- H-HO demixing in Uranus and Neptune: Adiabatic structure models
- TESS and HARPS reveal two sub-Neptunes around TOI 1062
- Observational constraints on the formation and evolution of Neptune-class exoplanets
- Super-Earth formation in systems with cold giants
- A Wide Orbit Exoplanet OGLE-2012-BLG-0838Lb
- NIRPS detection of delayed atmospheric escape from the warm and misaligned Saturn-mass exoplanet WASP-69b
- Planet Formation
- The Effect of Accretion Rate and Composition on the Structure of Ice-rich Super-Earths
- NIRPS tightens the mass estimate of GJ 3090 b and detects a planet near the stellar rotation period
- TFAW survey II: 6 Newly Validated Planets and 13 Planet Candidates from K2
- Possible in situ formation of Uranus and Neptune via Pebble Accretion
- Searching for GEMS: Three warm Saturns and a super-Jupiter orbiting four early M-dwarfs