Effects of Planetary Parameters on Disequilibrium Chemistry in Irradiated Planetary Atmospheres: From Gas Giants to Sub-Neptunes

A primary goal of characterizing exoplanet atmospheres is to constrain planetary bulk properties, such as their metallicity, C/O ratio, and intrinsic heat. However, there are significant uncertainties in many aspects of atmospheric physics, such as the strength of vertical mixing. Here we use PICASO and the photochem model to explore how atmospheric chemistry is influenced by planetary properties like metallicity, C/O ratio, T_int, T_eq, and K_zz in hydrogen-dominated atmospheres.

We vary the Teq of the planets between 400 K- 1600 K, across cold",warm,” and `hot” objects. We also explore an extensive range of Tint values between 30-500 K, representing sub-Neptunes to massive gas giants. We find that gases like CO and CO₂ show a drastically different dependence on K_zz and C/O for planets with cold interiors (e.g., sub-Neptunes) compared to planets with hotter interiors (e.g., Jupiter mass planets), for the same Teq.

We also find that gases like CS and CS₂ can carry a significant portion of the S- inventory in the upper atmosphere near T_eq ≤ 600 K, below which SO₂ ceases to be abundant. For solar C/O, we show that the CO/CH₄ ratio in the upper atmospheres of planets can become ≤1 for planets with low T_eq, but only if their interiors are cold (Tint≤100 K). We find that photochemical haze precursor molecules in the upper atmosphere show very complex dependence on C/O, Kzz, T_eq, and T_int for planets with cold interiors (e.g., sub-Neptunes).

We also briefly explore fully coupling PICASO and photochem to generate self-consistent radiative-convective-photochemical-equilibrium models.

The weighted abundance of CH₄ calculated using Equation 1 as a function of C/O and K_zz in each panel. Each row corresponds to a different T_eq value from 1100 K to 600 K from top to bottom. Each column correspond to a different T_int value between 30 K and 500 K from left to right. Note that the C/O is shown relative to an assumed solar value of 0.458 in this plot. — astro-ph.EP

Sagnick Mukherjee (1 and 2), Jonathan J. Fortney (1), Nicholas F. Wogan (3), David K. Sing (2), Kazumasa Ohno (4) ((1) University of California, Santa Cruz, (2) Johns Hopkins University, (3) NASA Ames Research Center, and (4) National Astronomical Observatory of Japan)

Comments: Revised and re-submitted to ApJ, Main text: Pages 1 to 34, 25 Figures, Appendix: Pages 35 to 36, 1 Figure
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2410.17169 [astro-ph.EP] (or arXiv:2410.17169v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2410.17169
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Submission history
From: Sagnick Mukherjee
[v1] Tue, 22 Oct 2024 16:49:42 UTC (10,442 KB)
https://arxiv.org/abs/2410.17169

Astrobiology, Astrochemistry,