Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b
High-resolution transmission spectroscopy of the warm gas giant WASP-69 b has revealed the presence of H _2 O, CO, CH _4 , NH _3 , and C _2 H _2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected...
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2025-01-01
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| author | Nidhi Bangera Christiane Helling Gloria Guilluy Patricio Cubillos Luca Fossati Paolo Giacobbe Paul Rimmer Daniel Kitzmann |
| author_facet | Nidhi Bangera Christiane Helling Gloria Guilluy Patricio Cubillos Luca Fossati Paolo Giacobbe Paul Rimmer Daniel Kitzmann |
| author_sort | Nidhi Bangera |
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| description | High-resolution transmission spectroscopy of the warm gas giant WASP-69 b has revealed the presence of H _2 O, CO, CH _4 , NH _3 , and C _2 H _2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO _2 , to constrain the atmospheric C/O ratio. We utilize nonequilibrium gas-phase simulations to conduct a parameter study for vertical diffusion strength, local gas temperature, and C/O ratio. Our results indicate that a carbon-rich atmosphere enhances CH _4 and C _2 H _2 concentrations, while NH _3 undergoes chemical conversion into HCN in carbon-rich, high-temperature environments. Consequently, HCN is abundantly produced in such atmospheres, though its strong spectral features remain undetected in WASP-69 b. Photochemical production of HCN and C _2 H _2 is highly sensitive to vertical diffusion strength, with weaker diffusion resulting in higher concentrations. Cross-correlation of synthetic spectra with observed data shows that models with C/O = 2 best match observations, but models with C/O = 0.55 and 0.9 lead to statistically equivalent fits, leaving the C/O ratio unconstrained. We highlight the importance of accurately modeling NH _3 quenching at pressures greater than 100 bars. Models for WASP-69 b capped at 100 bars bias cross-correlation fits toward carbon-rich values. We suggest that if the atmosphere of WASP-69 b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN. |
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| series | The Astrophysical Journal |
| spelling | doaj-art-3288bb3dcdc04396ac05d885b1115b082025-02-10T07:24:32ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01980114710.3847/1538-4357/adaa7dKinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 bNidhi Bangera0https://orcid.org/0009-0008-7545-5022Christiane Helling1https://orcid.org/0000-0002-8275-1371Gloria Guilluy2https://orcid.org/0000-0002-1259-2678Patricio Cubillos3https://orcid.org/0000-0002-1347-2600Luca Fossati4https://orcid.org/0000-0003-4426-9530Paolo Giacobbe5https://orcid.org/0000-0001-7034-7024Paul Rimmer6https://orcid.org/0000-0002-7180-081XDaniel Kitzmann7https://orcid.org/0000-0003-4269-3311Space Research Institute , Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria ; nidhirohit.bangera@oeaw.ac.at; Institute for Theoretical and Computational Physics, Graz University of Technology , Petersgasse 16, 8010 Graz, AustriaSpace Research Institute , Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria ; nidhirohit.bangera@oeaw.ac.at; Institute for Theoretical and Computational Physics, Graz University of Technology , Petersgasse 16, 8010 Graz, AustriaINAF—Osservatorio Astrofisico di Torino , Via Osservatorio 20, 10025, Pino Torinese, ItalySpace Research Institute , Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria ; nidhirohit.bangera@oeaw.ac.at; INAF—Osservatorio Astrofisico di Torino , Via Osservatorio 20, 10025, Pino Torinese, ItalySpace Research Institute , Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria ; nidhirohit.bangera@oeaw.ac.atINAF—Osservatorio Astrofisico di Torino , Via Osservatorio 20, 10025, Pino Torinese, ItalyCavendish Laboratory, University of Cambridge , JJ Thomson Ave., Cambridge, CB3 0HE, UKSpace Research and Planetary Sciences, Physics Institute, University of Bern , Gesellschaftsstrasse 6, 3012 Bern, Switzerland; Center for Space and Habitability, University of Bern , Gesellschaftsstrasse 6, 3012 Bern, SwitzerlandHigh-resolution transmission spectroscopy of the warm gas giant WASP-69 b has revealed the presence of H _2 O, CO, CH _4 , NH _3 , and C _2 H _2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO _2 , to constrain the atmospheric C/O ratio. We utilize nonequilibrium gas-phase simulations to conduct a parameter study for vertical diffusion strength, local gas temperature, and C/O ratio. Our results indicate that a carbon-rich atmosphere enhances CH _4 and C _2 H _2 concentrations, while NH _3 undergoes chemical conversion into HCN in carbon-rich, high-temperature environments. Consequently, HCN is abundantly produced in such atmospheres, though its strong spectral features remain undetected in WASP-69 b. Photochemical production of HCN and C _2 H _2 is highly sensitive to vertical diffusion strength, with weaker diffusion resulting in higher concentrations. Cross-correlation of synthetic spectra with observed data shows that models with C/O = 2 best match observations, but models with C/O = 0.55 and 0.9 lead to statistically equivalent fits, leaving the C/O ratio unconstrained. We highlight the importance of accurately modeling NH _3 quenching at pressures greater than 100 bars. Models for WASP-69 b capped at 100 bars bias cross-correlation fits toward carbon-rich values. We suggest that if the atmosphere of WASP-69 b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN.https://doi.org/10.3847/1538-4357/adaa7dChemical kineticsExoplanet atmospheresPlanetary atmospheres |
| spellingShingle | Nidhi Bangera Christiane Helling Gloria Guilluy Patricio Cubillos Luca Fossati Paolo Giacobbe Paul Rimmer Daniel Kitzmann Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b The Astrophysical Journal Chemical kinetics Exoplanet atmospheres Planetary atmospheres |
| title | Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b |
| title_full | Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b |
| title_fullStr | Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b |
| title_full_unstemmed | Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b |
| title_short | Kinetic and Photochemical Disequilibrium in the Potentially Carbon-rich Atmosphere of the Warm Jupiter WASP-69 b |
| title_sort | kinetic and photochemical disequilibrium in the potentially carbon rich atmosphere of the warm jupiter wasp 69 b |
| topic | Chemical kinetics Exoplanet atmospheres Planetary atmospheres |
| url | https://doi.org/10.3847/1538-4357/adaa7d |
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