Influence of sub- and super-solar metallicities on the compositions of solid planetary building blocks

Abstract

The composition of the protoplanetary disc is linked to the composition of the host star, where a higher overall metallicity of the host star provides more building blocks for planets. However, most planet formation simulations only link the stellar iron abundance [Fe/H] to planet formation and [Fe/H] in itself is used as a proxy to scale all elements. But large surveys of stellar abundances show that this is not true. We use here stellar abundances from the GALAH surveys to determine the average detailed abundances of Fe, Si, Mg, O, and C for a broad range of [Fe/H] spanning from -0.4 to +0.4. Using an equilibrium chemical model that features the most important rock forming molecules as well as volatile contributions of H${}_2$O, CO${}_2$, CH${}_4$ and CO, we calculate the chemical composition of solid planetary building blocks. Solid building blocks that are formed entirely interior to the water ice line (T>150K) only show an increase in Mg${}_2$SiO${}_4$ and a decrease in MgSiO${}_3$ for increasing host star metallicity, related to the increase of Mg/Si for higher [Fe/H]. Solid planetary building blocks forming exterior to the water ice line (T<150K) show dramatic changes in their composition. The water ice content decreases from around $\sim$50\% at [Fe/H]=-0.4 to $\sim$6\% at [Fe/H]=0.4 in our chemical model. This is mainly caused by the increasing C/O ratio with increasing [Fe/H], which binds most of the oxygen in gaseous CO and CO${}_2$, resulting in a small water ice fraction. Planet formation simulations coupled with the chemical model confirm these results by showing that the water ice content of super-Earths decreases with increasing host star metallicity due to the increased C/O ratio. This decrease of the water ice fraction has important consequences for planet formation, planetary composition and the eventual habitability of planetary systems formed around these high metallicity stars.

17 pages, accepted by A&A

References in corpus (42)

• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• Galactic chemical evolution: Carbon through Zinc
• Mass-Radius Relationships for Solid Exoplanets
• Growth Model Interpretation of Planet Size Distribution
• Separating gas-giant and ice-giant planets by halting pebble accretion
• Migration and the formation of systems of hot super-Earths and Neptunes
• Detailed Models of super-Earths: How well can we infer bulk properties?
• The structure of protoplanetary discs around evolving young stars
• Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion
• Planetesimal formation starts at the snow line
• Formation of planetary systems by pebble accretion and migration: How the radial pebble flux determines a terrestrial-planet or super-Earth growth mode
• Chemical enrichment of giant planets and discs due to pebble drift
• Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
• Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars
• Dust flow in gas disks in the presence of embedded planets
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• Formation of planetary systems by pebble accretion and migration: Growth of gas giants
• H2O abundances in the atmospheres of three hot Jupiters
• Hot super-Earths and giant planet cores from different migration histories
• Formation of dust-rich planetesimals from sublimated pebbles inside of the snow line
• The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk
• Mg line formation in late-type stellar atmospheres: I. The model atom
• A reassessment of the in situ formation of close-in super-Earths
• Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?
• Planet population synthesis driven by pebble accretion in cluster environments
• A new class of Super-Earths formed from high-temperature condensates: HD219134 b, 55 Cnc e, WASP-47 e
• Constraining planet structure and composition from stellar chemistry: trends in different stellar populations
• From planetesimals to planets: volatile molecules
• The solar silicon abundance based on 3D non-LTE calculations
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system
• Gas composition of main volatile elements in protoplanetary discs and its implication for planet formation
• Pebble-driven planet formation for TRAPPIST-1 and other compact systems
• Connecting planet formation and astrochemistry: Refractory carbon depletion leading to super-stellar C/O in giant planetary atmospheres
• Time evolution of snow regions and planet traps in an evolving protoplanetary disk
• Carbon and oxygen in metal-poor halo stars
• Disentangling Hot Jupiters formation location from their chemical composition
• Sulfur and zinc abundances of red giant stars
• The Metallicity-Period-Mass Diagram of low-mass exoplanets
• From the stellar properties of HD219134 to the internal compositions of its transiting exoplanets
• A revolution is brewing: observations of TRAPPIST-1 exoplanetary system fosters a new biomarker

Cited by in corpus (53)

• The GALAH+ Survey: Third Data Release
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants
• A new perspective on interiors of ice-rich planets: Ice-rock mixture instead of ice on top of rock
• How planets grow by pebble accretion. III. Emergence of an interior composition gradient
• Close-in ice lines and the super-stellar C/O ratio in discs around very low-mass stars
• Dry or water world? How the water contents of inner sub-Neptunes constrain giant planet formation and the location of the water ice line
• Setting the stage for the search for life with the Habitable Worlds Observatory: Properties of 164 promising planet survey targets
• Plausible constraints on the range of bulk terrestrial exoplanet compositions in the Solar neighbourhood
• Elemental abundances of nearby M dwarfs based on high-resolution near-infrared spectra obtained by the Subaru/IRD survey: Proof of concept
• Enriching inner discs and giant planets with heavy elements
• Chemical evolution in ices on drifting, planet-forming pebbles
• Forming super-Mercuries: The role of stellar abundances
• How does accretion of planet-forming disks influence stellar abundances?
• Forming planets around stars with non-solar elemental composition
• The water-ice line as a birthplace of planets: Implications of a species-dependent dust fragmentation threshold
• Burned to ashes: How the thermal decomposition of refractory organics in the inner protoplanetary disc impacts the gas-phase C/O ratio
• How the origin of stars in the Galaxy impacts the composition of planetary building blocks
• Planet formation throughout the Milky Way: Planet populations in the context of Galactic chemical evolution
• Chemical Composition Of Bright Stars In The Northern Hemisphere: Star-Planet Connection
• Chemical Composition of Bright Stars in the Continuous Viewing Zone of the TESS Space Mission
• Which stars can form planets: Planetesimal formation at low metallicities
• A hot mini-Neptune in the radius valley orbiting solar analogue HD 110113
• Changing disc compositions via internal photoevaporation I: Solar-mass stars
• The Galactic Interstellar Object Population: A Framework for Prediction and Inference
• Influence of grain sizes and composition on the contraction rates of planetary envelopes and on planetary migration
• The chemical evolution of the solar neighbourhood for planet-hosting stars
• Exoplanets Across Galactic Stellar Populations with PLATO: Estimating Exoplanet Yields Around FGK Stars for the Thin Disk, Thick Disk and Stellar Halo
• Locked In Ice: how Pebble Drift and Volatile Entrapment can Significantly Impact Carbon and Oxygen Ratios in Evolving Protoplanetary Discs
• Predicting Interstellar Object Chemodynamics with Gaia
• The GALAH Survey: Using Galactic Archaeology to Refine our Knowledge of TESS Target Stars
• Predicting the water content of interstellar objects from galactic star formation histories
• The growth of super-Earths: the importance of a self-consistent treatment of disc structures and pebble accretion
• Europium as a lodestar: diagnosis of radiogenic heat production in terrestrial exoplanets
• Ariel stellar characterisation II. Chemical abundances of carbon, nitrogen, and oxygen for 181 planet-host FGK dwarf stars
• Revisiting equilibrium condensation and rocky planet compositions: Introducing the ECCOplanets code
• Chemical evolution in planet-forming regions with growing grains
• Formation of Planetary Populations III: Core Composition & Atmospheric Evaporation
• Planetesimal formation via the streaming instability in simulations of infall dominated young disks
• How external photo-evaporation changes the chemical composition of the inner disc
• Chemical composition of planetary hosts: C, N, and $\alpha$-element abundances
• The GALAH Survey: Improving our understanding of confirmed and candidate planetary systems with large stellar surveys
• Changing disc compositions via internal photoevaporation II: M dwarf systems
• Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
• How does the chemical composition of solids influence the formation of planetesimals?
• Proto-planetary disk composition-dependent element volatility in the context of rocky planet formation
• How disc initial conditions sculpt the atmospheric composition of giant planets
• Towards characterising rocky worlds: Trends in chemical make-ups of M dwarfs versus GK dwarfs
• Constraining the formation history of the HAT-P-11 system by atmospheric abundances
• From CO${}_2$- to H${}_2$O-dominated atmospheres and back -- How mixed outgassing changes the volatile distribution in magma oceans around M dwarf stars
• Interpreting the atmospheric composition of exoplanets: sensitivity to planet formation assumptions
• A compositional link between rocky exoplanets and their host stars
• A close-encounter method for simulating the dynamics of planetesimals