The Effect of Accretion Rate and Composition on the Structure of Ice-rich Super-Earths

Abstract

It is reasonable to assume that the structure of a planet and the interior distribution of its components are determined by its formation history. We thus follow the growth of a planet from a small embryo through its subsequent evolution. We estimate the accretion rate range based on a protoplanetary disk model at a large enough distance from the central star, for water ice to be a major component. We assume the accreted material to be a mixture of silicate rock and ice, with no H-He envelope, as the accretion timescale is much longer than the time required for the nebular gas to dissipate. We adopt a thermal evolution model that includes accretional heating, radioactive energy release, and separation of ice and rock. Taking the Safronov parameter and the ice-to-rock ratio as free parameters, we compute growth and evolutionary sequences for different parameter combinations, for 4.6 Gyr. We find the final structure to depend significantly on both parameters. Low initial ice to rock ratios and high accretion rates, each resulting in increased heating rate, lead to the formation of extended rocky cores, while the opposite conditions leave the composition almost unchanged and result in relatively low internal temperatures. When rocky cores form, the ice-rich outer mantles still contain rock mixed with the ice. We find that a considerable fraction of the ice evaporates upon accretion, depending on parameters, and assume it is lost, thus the final surface composition and bulk density of the planet do not necessarily reflect the protoplanetary disk composition.

References in corpus (48)

• Disk Frequencies and Lifetimes in Young Clusters
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• The false positive rate of Kepler and the occurrence of planets
• Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
• Rapid growth of gas-giant cores by pebble accretion
• Models of Giant Planet formation with migration and disc evolution
• Internal Structure of Massive Terrestrial Planets
• Observations of Protoplanetary Disk Structures
• Can we constrain interior structure of rocky exoplanets from mass and radius measurements?
• A Framework for Quantifying the Degeneracies of Exoplanet Interior Compositions
• Characterization of exoplanets from their formation II: The planetary mass-radius relationship
• Solar System Abundances of the Elements
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• The radial dependence of pebble accretion rates: A source of diversity in planetary systems I. Analytical formulation
• The nature and origins of sub-Neptune size planets
• Jupiter's composition suggests its core assembled exterior to the N2 snowline
• Giant Planet Formation, Evolution, and Internal Structure
• The Effect of Composition on the Evolution of Giant and Intermediate-Mass Planets
• The formation of Jupiter by hybrid pebble-planetesimal accretion
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• Jupiter's formation and its primordial internal structure
• The origin of the high metallicity of close-in giant exoplanets: Combined effect of the resonant and aerodynamic shepherding
• Pebbles versus Planetesimals: The case of Trappist-1
• The formation of mini-Neptunes
• A new perspective on interiors of ice-rich planets: Ice-rock mixture instead of ice on top of rock
• Convection and Mixing in Giant Planet Evolution
• How planets grow by pebble accretion. III. Emergence of an interior composition gradient
• Jupiter formed as a pebble pile around the N${}_2$ ice line
• Threshold radii of volatile-rich planets
• The effect of temperature evolution on the interior structure of H${}_2$O-rich planets
• Contribution of the core to the thermal evolution of sub-Neptunes
• Susceptibility of planetary atmospheres to mass loss and growth by planetesimal impacts: the impact shoreline
• Giant planet formation models with a self-consistent treatment of the heavy elements
• Migration of Jupiter mass planets in low viscosity discs
• Atmosphere loss in planet-planet collisions
• Linking planetary embryo formation to planetesimal formation I: The impact of the planetesimal surface density in the terrestrial planet zone
• Linking planetary embryo formation to planetesimal formation II: The impact of pebble accretion in the terrestrial planet zone
• Probing protoplanetary disk evolution in the Chamaeleon II region
• The Formation of Uranus and Neptune: Fine Tuning in Core Accretion
• Losing Oceans: The Effects of Composition on the Thermal Component of Impact-driven Atmospheric Loss
• Atmosphere Loss in Oblique Super-Earth Impacts
• Effects of pebble accretion on the growth and composition of planetesimals in the inner Solar System
• Planetary core formation via multi-species pebble accretion
• Why do more massive stars host larger planets?
• Rapid-then-slow migration reproduces mass distribution of TRAPPIST-1 system
• Why hot Jupiters can be large but not too large
• Erosion driven size-redistribution of protoplanetary disk solids and the onset of streaming Instability and Pebble Accretion