Influence of C/O Ratio on Hot Jupiter Atmospheric Chemistry

Abstract

We have conducted laboratory experiments to study the chemistry in hot Jupiter atmospheres with C/O ratio of 0.35. We have compared our results with the ones obtained previously for atmospheres with a C/O ratio of 1 to investigate the influence of the C/O ratio on the chemistry and formation of photochemical organic aerosol. We found that the C/O ratio and the gas mixture compositions strongly influence the pathways responsible for the formation of CO2. Thermochemical reactions are primarily responsible for the formation of CO2 in low C/O ratio atmospheres, while photochemistry is the dominant process in high C/O ratio atmospheres even if the final CO2 concentration is the same in both cases. Our results show that low C/O atmospheres at the thermochemical equilibrium contain a higher water abundance, while high C/O atmospheres are significantly depleted in water. However, in low C/O atmospheres, the water abundance is not affected by UV photolysis, while our previous work demonstrated that significant amount of water can be produced in high C/O ratio atmospheres. This contrast in water production suggests that photochemistry should be considered when interpreting exoplanet transit spectra. Finally, we did not observe the formation of a detectable amount of non-volatile photochemical aerosols in low C/O atmospheres, in contrast to our previous study. We infer that for C/O ratio < 1, water likely inhibits organic growth and aerosol formation, suggesting that photochemical organic aerosols are likely to be observed in planets presenting a carbon enrichment compared to their host stars.

23 pages, 3 tables, 6 figures

References in corpus (11)

• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Rayleigh scattering in the transit spectrum of HD 189733b
• The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters
• VULCAN: an Open-Source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres
• A consistent retrieval analysis of 10 Hot Jupiters observed in transmission
• New chemical scheme for studying carbon-rich exoplanet atmospheres
• The effect of Lyman $\alpha$ radiation on mini-Neptune atmospheres around M stars: application to GJ 436b
• C/O and O/H Ratios Suggest Some Hot Jupiters Originate Beyond the Snow Line
• VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres
• Photochemistry in hot H2-dominated exoplanet atmospheres
• The carbon-to-oxygen ratio: implications for the spectra of hydrogen-dominated exoplanet atmospheres

Cited by in corpus (12)

• 3D simulations of photochemical hazes in the atmosphere of hot Jupiter HD 189733b
• Detection of an Atmosphere on a Rocky Exoplanet
• Observability of signatures of transport-induced chemistry in clear atmospheres of hot gas giant exoplanets
• Grid of Pseudo-2D Chemistry Models for Tidally-Locked Exoplanets. I. The Role of Vertical and Horizontal Mixing
• Grid of pseudo-2D chemistry models for tidally locked exoplanets -- II. The role of photochemistry
• A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres
• Photochemical hazes can trace the C/O ratio in exoplanet atmospheres
• Detection of Aerosols at Microbar Pressures in an Exoplanet Atmosphere
• 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)
• Probing Two-dimensional Asymmetries of an Exoplanet Atmosphere from Chromatic Transit Variation
• Experimental Investigation of the Photochemical Production of Hydrocarbons in Warm Gas Giant Exoplanet Atmospheres