Global Chemical Transport on Hot Jupiters: Insights from the 2D VULCAN Photochemical Model

Tsai, Shang-Min; Parmentier, Vivien; Mendonça, João M.; Tan, Xianyu; Deitrick, Russell; Hammond, Mark; Savel, Arjun B.; Zhang, Xi; Pierrehumbert, Raymond T.; Schwieterman, Edward W.

doi:10.3847/1538-4357/ad1600

Cited by 5 publications

(3 citation statements)

References 80 publications

(133 reference statements)

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“…In cases of nonsynchronous or ultrahot atmospheres that experience strong magnetic drag, the main circulation pattern deviates from equatorial superrotation. Horizontal transport in such conditions can make distinct characteristics compared to the revolving transport by a zonal jet, which will be addressed in a separate paper (Tsai et al 2024). Furthermore, although the same thermal and wind structures are used in this 2D study while exploring metallicity, we expect similar general transport properties with this small metallicity variation.…”

Section: Discussionmentioning

confidence: 89%

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Day–Night Transport-induced Chemistry and Clouds on WASP-39b: Gas-phase Composition

Tsai,

Moses,

Powell

et al. 2023

ApJL

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JWST has recently detected the first robust photochemical product on an exoplanet: sulfur dioxide (SO2) on WASP-39b. The data from the NIRISS instrument also reveal signs of partial coverage of clouds. Most of the previous studies have focused on interpreting spectral data with 1D models. To explore how the chemical species and cloud particles are altered by global circulation, we applied a 2D photochemical model and a 2D microphysical cloud model separately to postprocess the thermal and dynamical structures simulated by a 3D general circulation model of WASP-39b. We found that SO2 produced by photochemistry on the dayside can be transported to the nightside owing to the efficient replenishment of horizontal transport. The morning–evening limb differences in methane (CH4) abundances predicted by the 1D models disappeared after horizontal transport is included. Similarly, the inclusion of horizontal transport also reduced the limb differences in SO2. Our modeling results suggest that the fast zonal wind results in minimal or negligible limb asymmetry in composition. Based on the synthetic spectra generated by our 2D atmosphere simulations, we propose that observing SO2 absorption in the emission spectra of WASP-39b at different phases may offer opportunities to probe the horizontal quenching process of photochemical products. We will focus on the gas-phase chemistry in this paper and leave the results regarding clouds in the subsequent paper as part of the series.

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Section: Discussionmentioning

confidence: 89%

“…When varying atmospheric metallicity in the 2D VULCAN model later, we adopted identical GCM outputs based on 10×solar metallicity. The construction and validation of 2D VULCAN are presented in detail in a separate paper Tsai et al (2024).…”

Section: D Photochemistrymentioning

confidence: 99%

Day–Night Transport-induced Chemistry and Clouds on WASP-39b: Gas-phase Composition

Tsai,

Moses,

Powell

et al. 2023

ApJL

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“…Global circulation plays a central role in transporting species between the dayside and nightside, where distinct chemical sources and sinks are at play (Chen et al 2018;Tsai et al 2021bTsai et al , 2023c. To account for the day-night transport, we run VULCAN 2D (Tsai et al 2021b(Tsai et al , 2024 to model the equatorial region, using temperature and wind structures from the 3D general circulation model (GCM) Exo-FMS (Lee et al 2021;Innes & Pierrehumbert 2022) as input.…”

Section: D Gcm 2d Photochemical Modelmentioning

confidence: 99%

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

Tsai,

Innes,

Wogan

et al. 2024

ApJL

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Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (≳20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH4, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C2H4) and ethane (C2H6), in the mid-infrared between 9 and 13 μm.

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Photodissociation and induced chemical asymmetries on ultra-hot gas giants

Baeyens,

Désert,

Petrignani

et al. 2024

A&A

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Recent observations have resulted in the detection of chemical gradients on ultra-hot gas giants. Notwithstanding their high temperature, chemical reactions in ultra-hot atmospheres may occur in disequilibrium, due to vigorous day-night circulation and intense UV radiation from their stellar hosts. The goal of this work is to explore whether photochemistry is affecting the composition of ultra-hot giant planets, and if it can introduce horizontal chemical gradients. In particular, we focus on hydrogen cyanide (HCN) on WASP-76 b, as it is a photochemically active molecule with a reported detection on only one side of this planet. We used a pseudo-2D chemical kinetics code to model the chemical composition of WASP-76 b along its equator. Our approach improved on chemical equilibrium models by computing vertical mixing, horizontal advection, and photochemistry. We find that the production of HCN is initiated through the thermal and photochemical dissociation of CO and N_2 on the day side of WASP-76 b. The resulting radicals are subsequently transported to the night side via the equatorial jet stream, where they recombine into different molecules. This process results in an HCN gradient with a maximal abundance on the planet's morning limb. We verified that photochemical dissociation is a necessary condition for this mechanism, as thermal dissociation alone proves insufficient. Other species produced via night-side disequilibrium chemistry are SO_2 and S_2 Our model acts as a proof of concept for chemical gradients on ultra-hot exoplanets. We demonstrate that even ultra-hot planets can exhibit disequilibrium chemistry and recommend that future studies do not neglect photochemistry in their analyses of ultra-hot planets.

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Global Chemical Transport on Hot Jupiters: Insights from the 2D VULCAN Photochemical Model

Cited by 5 publications

References 80 publications

Day–Night Transport-induced Chemistry and Clouds on WASP-39b: Gas-phase Composition

Day–Night Transport-induced Chemistry and Clouds on WASP-39b: Gas-phase Composition

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

Photodissociation and induced chemical asymmetries on ultra-hot gas giants

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