Burned to ashes: How the thermal decomposition of refractory organics in the inner protoplanetary disc impacts the gas-phase C/O ratio

Abstract

The largest reservoir of carbon in protoplanetary discs is stored in refractory organics, which thermally decompose into the gas-phase at the organics line, well interior to the water iceline. Because this region is so close to the host star, it is often assumed that the released gaseous material is rapidly accreted and plays little role in the evolution of the disc composition. However, laboratory experiments show that the thermal decomposition process is irreversible, breaking macromolecular refractory organics into simpler, volatile carbon-bearing compounds. As a result, unlike the iceline of other volatiles, which traps vapor inwards due to recondensation, the organics line remains permeable, allowing gaseous carbon to diffuse outward without returning to the solid phase. In this paper, we investigate how this process affects the disc composition, particularly the gas-phase C/H and C/O ratios, by incorporating it into a 1D evolution model for gas and solids, and assuming refractory organics dominantly decompose into C${}_2$H${}_2$. Our results show that this process allows this carbon-rich gas to survive well beyond the organics line (out to $7\mathrm{au}$ around a solar-mass star) and for much longer timescales, such that its abundance is increased by an order of magnitude. This has several implications in planet formation, notably by altering how the composition of solids and gas relate, and the fraction of heavy elements available to giant planets. In the framework of our model, refractory organics significantly influence the evolution of the gas-phase C/O ratio, which may help interpreting measurements made with Spitzer and JWST.

arXiv commentAccepted for publication in A&A. 18 pages, 14 figures, 1 table

References in corpus (82)

• The chemical composition of the Sun
• The Spitzer Space Telescope Mission
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The effects of snowlines on C/O in planetary atmospheres
• A simple model for the evolution of the dust population in protoplanetary disks
• New Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints
• C/O ratio as a Dimension for Characterizing Exoplanetary Atmospheres
• The Mass-Metallicity Relation for Giant Planets
• Towards Chemical Constraints on Hot Jupiter Migration
• Planetesimal formation starts at the snow line
• Astrochemistry and compositions of planetary systems
• Dust size distributions in coagulation/fragmentation equilibrium: Numerical solutions and analytical fits
• Chemical enrichment of giant planets and discs due to pebble drift
• Material enhancement in protoplanetary nebulae by particle drift through evaporation fronts
• Tracing the Ingredients for a Habitable Earth from Interstellar Space through Planet Formation
• A Spitzer Survey of Mid-Infrared Molecular Emission from Protoplanetary Disks II: Correlations and LTE Models
• The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime
• Resolving the Luminosity Problem in Low-Mass Star Formation
• The Different Evolution of Gas and Dust in Disks around Sun-like and Cool Stars
• Elemental and molecular abundances in comet 67P/Churyumov-Gerasimenko
• Dust diffusion in protoplanetary discs by magnetorotational turbulence
• Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
• Contacts of Water Ice in Protoplanetary Disks - Laboratory Experiments
• Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• Dust evolution in protoplanetary disks around Herbig Ae/Be stars - The Spitzer view
• The Nature of Transition Circumstellar Disks I. The Ophiuchus Molecular Cloud
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• Planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift
• The ice composition in the disk around V883 Ori revealed by its stellar outburst
• Transport of CO in Protoplanetary Disks: Consequences of Pebble Formation, Settling, and Radial Drift
• Sensitivity analysis of grain surface chemistry to binding energies of ice species
• A recent accretion burst in the low-mass protostar IRAS 15398-3359: ALMA imaging of its related chemistry
• Two-Dimensional Transport of Solids in Viscous Protoplanetary Disks
• The Atomic and Molecular Content of Disks Around Very Low-mass Stars and Brown Dwarfs
• Water in the terrestrial planet-forming zone of the PDS 70 disk
• Protoplanetary disc `isochrones' and the evolution of discs in the $\dot{M}-M_{\mathrm{d}}$ plane
• Methanol and its relation to the water snowline in the disk around the young outbursting star V883 Ori
• How drifting and evaporating pebbles shape giant planets II: Volatiles and refractories in atmospheres
• Influence of sub- and super-solar metallicities on the compositions of solid planetary building blocks
• The HCN-Water Ratio in the Planet Formation Region of Disks
• Temperature Structure in the Inner Regions of Protoplanetary Disks: Inefficient Accretion Heating Controlled by Nonideal Magnetohydrodynamics
• The Solar Nebula on Fire: A Solution to the Carbon Deficit in the Inner Solar System
• Dust Transport in MRI Turbulent Disks: Ideal and Non-ideal MHD with Ambipolar Diffusion
• Abundant hydrocarbons in the disk around a very-low-mass star
• Destruction of Refractory Carbon in Protoplanetary Disks
• Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc
• The spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals
• Close-in ice lines and the super-stellar C/O ratio in discs around very low-mass stars
• Determining the recurrence timescale of long-lasting YSO outbursts
• The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability
• Chemical Signatures of the FU Ori Outbursts
• MINDS. Hydrocarbons detected by JWST/MIRI in the inner disk of Sz28 consistent with a high C/O gas-phase chemistry
• Luminosity outburst chemistry in protoplanetary discs: going beyond standard tracers
• Radial and vertical dust transport inhibit refractory carbon depletion in protoplanetary disks
• 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
• Collisional evolution of dust and water ice in protoplanetary discs during and after an accretion outburst
• Enriching inner discs and giant planets with heavy elements
• Dust mineralogy and variability of the inner PDS 70 disk
• Composition of giant planets: the roles of pebbles and planetesimals
• Atmospheric Recyling of Volatiles by Pebble-Accreting Planets
• Dust crystallinity in protoplanetary disks: the effect of diffusion/viscosity ratio
• Hydrocarbon chemistry in inner regions of planet forming disks
• CO2-rich protoplanetary discs as a probe of dust radial drift & trapping
• Water UV-shielding in the terrestrial planet-forming zone: Implications for carbon dioxide emission
• PENELLOPE III. The peculiar accretion variability of XX Cha and its impact on the observed spread of accretion rates
• MINDS: The very low-mass star and brown dwarf sample -- Hidden water in carbon-dominated protoplanetary disks
• Carbon Depletion in the Early Solar System
• Anatomy of rocky planets formed by rapid pebble accretion III. Partitioning of volatiles between planetary core, mantle, and atmosphere
• Thermal processing of primordial pebbles in evolving protoplanetary disks
• Changing disc compositions via internal photoevaporation I: Solar-mass stars
• Exploring the Origins of Earth's Nitrogen: Astronomical Observations of Nitrogen-bearing Organics in Protostellar Environments
• Water UV-Shielding in the Terrestrial Planet-Forming Zone: Implications for Oxygen-18 Isotope Anomalies in H2-18O Infrared Emission and Meteorites
• Refractory carbon depletion by photolysis through dust collisions and vertical mixing
• Fast formation of large ice pebbles after FU Orionis outbursts
• The Efficiency of Noble Gas Trapping in Astrophysical Environments
• Effects from different grades of stickiness between icy and silicate particles on carbon depletion in protoplanetary disks
• Dust evolution by chemisputtering during protostellar formation
• Tracking the Chemical Evolution of Hydrocarbons Through Carbon Grain Supply in Protoplanetary Disks
• UV-processing of icy pebbles in the outer parts of VSI-turbulent disks

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• Chemical transformation of CO in evolving protoplanetary discs across stellar masses: a route to C-rich inner regions
• Planet formation in chemically diverse and evolving discs -- I. Composition of planetary building blocks
• MINDS. Strong oxygen depletion in the inner regions of a very low-mass star disk?
• Changing disc compositions via internal photoevaporation II: M dwarf systems
• How disc initial conditions sculpt the atmospheric composition of giant planets
• 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
• MINDS survey of silicates in T Tauri disks: Correlation between dust and gas