The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs

Abstract

The radial-dependent positions of snowlines of abundant oxygen- and carbon-bearing molecules in protoplanetary discs will result in systematic radial variations in the C/O ratios in the gas and ice. This variation is proposed as a tracer of the formation location of gas-giant planets. However, disc chemistry can affect the C/O ratios in the gas and ice, thus potentially erasing the chemical fingerprint of snowlines in gas-giant atmospheres. We calculate the molecular composition of hot Jupiter atmospheres using elemental abundances extracted from a chemical kinetics model of a disc midplane where we have varied the initial abundances and ionization rates. The models predict a wider diversity of possible atmospheres than those predicted using elemental ratios from snowlines only. As found in previous work, as the C/O ratio exceeds the solar value, the mixing ratio of CH${}_4$ increases in the lower atmosphere, and those of C${}_2$H${}_2$ and HCN increase mainly in the upper atmosphere. The mixing ratio of H${}_2$O correspondingly decreases. We find that hot Jupiters with C/O$>1$ can only form between the CO${}_2$ and CH${}_4$ snowlines. Moreover, they can only form in a disc which has fully inherited interstellar abundances, and where negligible chemistry has occurred. Hence, carbon-rich planets are likely rare, unless efficient transport of hydrocarbon-rich ices via pebble drift to within the CH${}_4$ snowline is a common phenomenon. We predict combinations of C/O ratios and elemental abundances that can constrain gas-giant planet formation locations relative to snowline positions, and that can provide insight into the disc chemical history.

18 pages, 7 figures, and 2 tables are contained in this paper. It was accepted for publication in MNRAS on September 18th, 2020

References in corpus (35)

• On the radiative equilibrium of irradiated planetary atmospheres
• A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters
• Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b
• A chemical model for the atmosphere of hot Jupiters
• Chemical enrichment of giant planets and discs due to pebble drift
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• VULCAN: an Open-Source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres
• Meridional flows in the disk around a young star
• Atom addition reactions in interstellar ice analogues
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
• Formation of a disc gap induced by a planet: Effect of the deviation from Keplerian disc rotation
• The water abundance in Jupiter's equatorial zone
• Discovery of water at high spectral resolution in the atmosphere of 51 Peg b
• Planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift
• Jupiter's composition suggests its core assembled exterior to the N2 snowline
• Excess C/O and C/H in outer protoplanetary disk gas
• Disk evolution, element abundances and cloud properties of young gas giant planets
• Exoplanet atmospheres with GIANO II. Detection of molecular absorption in the dayside spectrum of HD 102195b
• Connecting planet formation and astrochemistry: A main sequence for C/O in hot-exoplanetary atmospheres
• C/O and O/H Ratios Suggest Some Hot Jupiters Originate Beyond the Snow Line
• The Role of Ice Compositions for Snowlines and the C/N/O Ratios in Active Disks
• Jupiter formed as a pebble pile around the N${}_2$ ice line
• Measuring Jupiter's water abundance by Juno: the link between interior and formation models
• Connecting planet formation and astrochemistry: Refractory carbon depletion leading to super-stellar C/O in giant planetary atmospheres
• The chemistry of protoplanetary fragments formed via gravitational instabilities
• Signatures of Nitrogen Chemistry in Hot Jupiter Atmospheres
• Candidate Water Vapor Lines to Locate the H${}_2$O Snowline through High-Dispersion Spectroscopic Observations II. The Case of a Herbig Ae Star
• A chemical kinetics code for modelling exoplanetary atmospheres
• The carbon-to-oxygen ratio: implications for the spectra of hydrogen-dominated exoplanet atmospheres
• Dust continuum emission and the upper limit fluxes of sub-millimeter water lines of the protoplanetary disk around HD 163296 observed by ALMA
• Spectroscopic Coronagraphy for Planetary Radial Velocimetry of Exoplanets
• Pebble accretion in class 0/I YSOs as a possible pathway for early planet formation

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• How drifting and evaporating pebbles shape giant planets II: Volatiles and refractories in atmospheres
• Evidence that the Hot Jupiter WASP-77 A b Formed Beyond Its Parent Protoplanetary Disk's H2O Ice Line
• Jupiter's "Cold" Formation in the Protosolar Disk Shadow: An Explanation for the Planet's Uniformly Enriched Atmosphere
• System-level fractionation of carbon from disk and planetesimal processing
• Formation of dust clumps with sub-Jupiter mass and cold shadowed region in gravitationally unstable disk around Class 0/I protostar in L1527 IRS
• The origin of the high metallicity of close-in giant exoplanets II The nature of the sweet spot for accretion
• The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline
• Tracing the formation and migration history: molecular signatures in the atmosphere of misaligned hot Jupiter WASP-94Ab using JWST NIRSpec/G395H
• Ariel stellar characterisation II. Chemical abundances of carbon, nitrogen, and oxygen for 181 planet-host FGK dwarf stars
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• Zodiacal Exoplanets in Time (ZEIT) XII: A Directly-Imaged Planetary-Mass Companion to a Young Taurus M Dwarf Star
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