Composition of giant planets: the roles of pebbles and planetesimals

Abstract

One of the current challenges of planet formation theory is to explain the enrichment of observed exoplanetary atmospheres. Past studies have focused on scenarios where either pebbles or planetesimals were the heavy element enrichment's drivers, we combine here both approaches to understand whether the composition of a planet can constrain its formation pathway. We study three different formation scenarios: pebble accretion, pebble accretion with planetesimal formation, combined pebble and planetesimal accretion. We use the chemcomp code to perform semi-analytical 1D simulations of protoplanetary discs, including viscous evolution, pebble drift, and simple chemistry to simulate the growth of planets from planetary embryos to gas giants as they migrate through the disc, while tracking their composition. Our simulations confirm that the composition of the planetary atmosphere is dominated by the accretion of gas enriched by inward drifting and evaporating pebbles. Including planetesimal formation hinders the enrichment, because the pebbles locked into planetesimals cannot evaporate and enrich the disc. This results in a big drop of the accreted heavy elements both in the planetesimal formation and accretion case, proving that planetesimal formation needs to be inefficient in order to explain planets with high heavy element content. Accretion of planetesimals enhances the refractory component of the atmosphere, leading to low volatile to refractory ratios, contrary to the pure pebble scenario. Such low volatile to refractory ratios can also be achieved by planets migrating in the inner disc in pure pebble scenario. Distinguishing these two scenarios requires knowledge about the planet's atmospheric C/H and O/H ratios, which are higher for pure pebble accretion. Therefore, a detailed knowledge of the composition of planetary atmospheres could help to constrain the planet's formation pathway.

arXiv comment12 pages, 10 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (44)

• The effects of snowlines on C/O in planetary atmospheres
• Rapid growth of gas-giant cores by pebble accretion
• A simple model for the evolution of the dust population in protoplanetary disks
• The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks
• A torque formula for non-isothermal Type I planetary migration - II. Effects of diffusion
• Separating gas-giant and ice-giant planets by halting pebble accretion
• The Mass-Metallicity Relation for Giant Planets
• Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core
• Pebble isolation mass --- scaling law and implications for the formation of super-Earths and gas giants
• The structure of protoplanetary discs around evolving young stars
• Planetesimal formation starts at the snow line
• Characterization of exoplanets from their formation II: The planetary mass-radius relationship
• The New Generation Planetary Population Synthesis (NGPPS). I. Bern global model of planet formation and evolution, model tests, and emerging planetary systems
• Contacts of Water Ice in Protoplanetary Disks - Laboratory Experiments
• A solar C/O and sub-solar metallicity in a hot Jupiter atmosphere
• Atmospheric Signatures of Giant Exoplanet Formation by Pebble Accretion
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• Modeling the Formation of Giant Planet Cores I: Evaluating Key Processes
• Planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift
• Jupiter's evolution with primordial composition gradients
• How much does turbulence change the pebble isolation mass for planet formation?
• Where is the Water? Jupiter-like C/H ratio but strong H${}_2$O depletion found on $\tau$ Boötis b using SPIRou
• Coorbital thermal torques on low-mass protoplanets
• Accretion and destruction of planetesimals in turbulent disks
• The opacity of grains in protoplanetary atmospheres
• How drifting and evaporating pebbles shape giant planets II: Volatiles and refractories in atmospheres
• Planetesimal Population Synthesis: Pebble Flux Regulated Planetesimal Formation
• Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants
• Leaky dust traps: How fragmentation impacts dust filtering by planets
• Close-in ice lines and the super-stellar C/O ratio in discs around very low-mass stars
• High atmospheric metal enrichment for a Saturn-mass planet
• Jupiter's heavy-element enrichment expected from formation models
• Exploring the conditions for forming cold gas giants through planetesimal accretion
• How drifting and evaporating pebbles shape giant planets III: The formation of WASP-77A b and $\tau$ Boötis b
• How to make giant planets via pebble accretion
• Probing the impact of varied migration and gas accretion rates for the formation of giant planets in the pebble accretion scenario
• Chemical evolution in ices on drifting, planet-forming pebbles
• How planets grow by pebble accretion IV: Envelope opacity trends from sedimenting dust and pebbles
• Constraining the origin of giant exoplanets via elemental abundance measurements
• How does accretion of planet-forming disks influence stellar abundances?
• Exoplanet Interior Retrievals: core masses and metallicities from atmospheric abundances
• The interplay between pebble and planetesimal accretion in population synthesis models and its role in giant planet formation
• In-situ enrichment in heavy elements of hot Jupiters
• An Approximation for the Capture Radius of Gaseous Protoplanets

Cited by in corpus (13)

• Mind the gap: Distinguishing disc substructures and their impact on the inner disc composition
• BOWIE-ALIGN: How formation and migration histories of giant planets impact atmospheric compositions
• Burned to ashes: How the thermal decomposition of refractory organics in the inner protoplanetary disc impacts the gas-phase C/O ratio
• BOWIE-ALIGN: JWST reveals hints of planetesimal accretion and complex sulphur chemistry in the atmosphere of the misaligned hot Jupiter WASP-15b
• Locked In Ice: how Pebble Drift and Volatile Entrapment can Significantly Impact Carbon and Oxygen Ratios in Evolving Protoplanetary Discs
• ExoLyn: a golden mean approach to multi-species cloud modelling in atmospheric retrieval
• There is no disk mass budget problem of planet formation
• Planet formation in chemically diverse and evolving discs -- I. Composition of planetary building blocks
• C/O ratios in self-gravitating protoplanetary discs with dust evolution
• How disc initial conditions sculpt the atmospheric composition of giant planets
• Evidence of a gap in the envelope mass fraction of sub-Saturns
• How leaky? A large parameter study of leaky dust traps to quantify the transport of pebbles and ice in protoplanetary discs
• Icy Volatile Enhancements in Evolving Protoplanetary Disks