Chemical mapping of temperate sub-Neptune atmospheres: Constraining the deep-interior H2O/H2 using the atmospheric CO2/CH4
arXiv:2406.01955 · doi:10.3847/2041-8213/ad6b25
Abstract
Understanding the planetary envelope composition of sub-Neptune-type exoplanets is challenging due to the inherent degeneracy in their interior composition scenarios. Particularly, the planetary envelope's H2O/H2 ratio, which can also be expressed as the O/H ratio, provides crucial insights into its original location relative to the ice line during planetary formation. Using self-consistent radiative transfer modeling and a rate-based automatic chemical network generator combined with 1D photochemical kinetic-transport atmospheric modeling, we investigate various atmospheric scenarios of temperate sub-Neptunes, ranging from H2-dominated to H2O-dominated atmospheres with equilibrium temperatures (Teq) of 250-400 K. This study includes examples such as K2-18 b (Teq = 255 K), LP 791-18 c (Teq = 324 K), and TOI-270 d (Teq = 354 K). Our models indicate that the atmospheric CO2/CH4 ratio can be used to infer the deep-interior H2O/H2 ratio. Applying this method to recent JWST observations, our findings suggest K2-18 b likely has an interior that is 50% highly enriched in water, exceeding the water content in a 100xZ scenario and suggesting a planetary formation mechanism involving substantial accretion of ices. In contrast, our model suggests that approximately 25% of TOI-270 d's interior is composed of H2O, which aligns with the conventional metallicity framework with a metallicity higher than 100xZ. Furthermore, our models identify carbonyl sulfide (OCS) and sulfur dioxide (SO2) as strong indicators for temperate sub-Neptunes with at least 10% of their interior composed of water. These results provide a method to delineate the internal composition and formation mechanisms of temperate sub-Neptunes (Teq < ~500 K) via atmospheric characterization through transmission spectroscopy.
arXiv comment12 pages, 5 figures, accepted to be published in ApJL
References in corpus (54)
- The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
- Abundances of the elements in the solar system
- The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
- An asteroseismic view of the radius valley: stripped cores, not born rocky
- Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
- Separating gas-giant and ice-giant planets by halting pebble accretion
- The Mass-Metallicity Relation for Giant Planets
- Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
- Compositional diversity in the atmospheres of hot Neptunes, with application to GJ 436b
- Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
- Water Vapor and Clouds on the Habitable-Zone Sub-Neptune Exoplanet K2-18b
- Photochemistry in Terrestrial Exoplanet Atmospheres I: Photochemistry Model and Benchmark Cases
- Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
- The great dichotomy of the Solar System: small terrestrial embryos and massive giant planet cores
- Photochemically-produced SO in the atmosphere of WASP-39b
- Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
- Three Possible Origins for the Gas Layer on GJ 1214b
- A chemical model for the atmosphere of hot Jupiters
- The Atmospheric Signatures of Super-Earths: How to Distinguish Between Hydrogen-Rich and Hydrogen-Poor Atmospheres
- Composition and fate of short-period super-Earths: The case of CoRoT-7b
- Early Release Science of the exoplanet WASP-39b with JWST NIRISS
- The MUSCLES Treasury Survey III: X-ray to Infrared Spectra of 11 M and K Stars Hosting Planets
- VULCAN: an Open-Source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres
- Early Release Science of the exoplanet WASP-39b with JWST NIRCam
- Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
- Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type
- Photochemistry in Terrestrial Exoplanet Atmospheres III: Photochemistry and Thermochemistry in Thick Atmospheres on Super Earths and Mini Neptunes
- Habitability and Biosignatures of Hycean Worlds
- Photochemistry in Terrestrial Exoplanet Atmospheres II: H2S and SO2 Photochemistry in Anoxic Atmospheres
- Thermochemistry and Photochemistry in Cooler Hydrogen Dominated Extrasolar Planets: The Case of GJ436b
- Condensation-inhibited convection in hydrogen-rich atmospheres: Stability against double-diffusive processes and thermal profiles for Jupiter, Saturn, Uranus, and Neptune
- Connecting Giant Planet Atmosphere and Interior Modeling: Constraints on Atmospheric Metal Enrichment
- Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
- A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270
- A High Internal Heat Flux and Large Core in a Warm Neptune Exoplanet
- Global-mean Vertical Tracer Mixing in Planetary Atmospheres I: Theory and Fast-rotating Planets
- Sulphur dioxide in the mid-infrared transmission spectrum of WASP-39b
- Photolytic Hazes in the Atmosphere of 51 Eri b
- A warm Neptune's methane reveals core mass and vigorous atmospheric mixing
- Photochemistry of Anoxic Abiotic Habitable Planet Atmospheres: Impact of New HO Cross-Sections
- Distinguishing oceans of water from magma on mini-Neptune K2-18b
- Towards Consistent Modeling of Atmospheric Chemistry and Dynamics in Exoplanets: Validation and Generalization of Chemical Relaxation Method
- Unveiling shrouded oceans on temperate sub-Neptunes via transit signatures of solubility equilibria vs. gas thermochemistry
- How to identify exoplanet surfaces using atmospheric trace species in hydrogen-dominated atmospheres
- On the Composition of Young, Directly Imaged Giant Planets
- A super-Earth and sub-Neptune transiting the late-type M dwarf LP 791-18
- Clouds and Clarity: Revisiting Atmospheric Feature Trends in Neptune-size Exoplanets
- The runaway greenhouse on subNeptune waterworlds
- A 3D picture of moist-convection inhibition in hydrogen-rich atmospheres: Implications for K2-18 b
- Consistently Simulating a Wide Range of Atmospheric Scenarios for K2-18b with a Flexible Radiative Transfer Module
- Information in the Reflected Light Spectra of Widely Separated Giant Exoplanets
- Where are the Water Worlds?: Self-Consistent Models of Water-Rich Exoplanet Atmospheres
- Automated chemical reaction network generation and its application to exoplanet atmospheres
- High-fidelity reaction kinetic modeling of hot-Jupiter atmospheres incorporating thermal and UV photochemistry enhanced by metastable CO(a3Pi)
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- Constraining exoplanet interiors using observations of their atmospheres
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- Diversity in the haziness and chemistry of temperate sub-Neptunes
- Deciphering Sub-Neptune Atmospheres: New Insights from Geochemical Models of TOI-270 d
- The SPACE Program. I. The featureless spectrum of HD 86226 c challenges sub-Neptune atmosphere trends
- Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System
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- Sub-Neptunes as Soot Factories: Deep Atmosphere Hydrocarbon Formation and Quenching as the Origin of Sub-Neptune Aerosol Trends
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