Kinetic And Photochemical Disequilibrium In The Potentially Carbon-rich Atmosphere Of The Warm-Jupiter WASP-69b
High-resolution transmission spectroscopy of the warm gas-giant WASP-69b has revealed the presence of H2O, CO, CH4, NH3, and C2H2 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 CO2, to constrain the atmospheric C/O ratio. We utilize non-equilibrium 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 CH4 and C2H2 concentrations, while NH3 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-69b.
Photochemical production of HCN and C2H2 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 NH3 quenching at pressures greater than 100 bars. Models for WASP-69b capped at 100 bars bias cross-correlation fits towards carbon-rich values. We suggest that if the atmosphere of WASP-69b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN.
Nidhi Bangera, Christiane Helling, Gloria Guilluy, Patricio Cubillos, Luca Fossati, Paolo Giacobbe, Paul Rimmer, Daniel Kitzmann
Comments: 22 pages, 11 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.08463 [astro-ph.EP] (or arXiv:2501.08463v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.08463
Focus to learn more
Submission history
From: Nidhi Bangera
[v1] Tue, 14 Jan 2025 22:20:37 UTC (1,912 KB)
https://arxiv.org/abs/2501.08463
Astrobiology
