Exoplanetology: Exoplanets & Exomoons

Ab Initio Quantum Dynamics as a Scalable Solution to the Exoplanet Opacity Challenge: A Case Study of CO2 in Hydrogen Atmosphere

By Keith Cowing
Status Report
astro-ph.EP
September 9, 2024
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Ab Initio Quantum Dynamics as a Scalable Solution to the Exoplanet Opacity Challenge: A Case Study of CO2 in Hydrogen Atmosphere
Perturbation analysis via injection-retrieval to assess the precision required on the broadening parameters in the JWST era. Top Left: Synthetic transmission spectrum of a warm-Jupiter spanning NIRSpec and MIRI bands used for the retrieval. The blue line represents the best-fit model obtained when cross-retrieved with the CSd3.00 cross-sections. Bottom Left: Deviation of the residual corresponding to the best fit presented on the upper panel. No structure is seen due to parameter compensation as highlighted in N22. Top Right: Posterior probability distributions for the mixing ratio of CO2 for 15 different cross-sections showing increased levels of biases with increased perturbation. The dotted black line represents the ‘truth’ used for generating the synthetic spectrum. Overall variation of ∼1 dex is seen among the retrieved molecular abundance, consistent with N22. Bottom Right: Same for H2O. A similar variation of ∼1 dex overall, though leading to more significant biases due to the narrower distributions than for CO2. — astro-ph.EP

Light-matter interactions lie at the heart of our exploration of exoplanetary atmospheres. Interpreting data obtained by remote sensing is enabled by meticulous, time- and resource-consuming work aiming at deepening our understanding of such interactions (i.e., opacity models).

Recently, Niraulam2022 pointed out that due primarily to limitations on our modeling of broadening and far-wing behaviors, opacity models needed a timely update for exoplanet exploration in the JWST era, and thus argued for a scalable approach.

In this Letter, we introduce an end-to-end solution from ab initio calculations to pressure broadening, and use the perturbation framework to identify the need for precision to a level of ∼10%. We focus on the CO2-H2 system as CO2 presents a key absorption feature for exoplanet research (primarily driven by the observation of gas giants) at ∼4.3μm and yet severely lack opacity data.

We compute elastic and inelastic cross-sections for the collision of ortho-H2 ~with CO2, in the ground vibrational state, and at the coupled-channel fully converged level. For scattering energies above ∼20~cm−1, moderate precision inter-molecular potentials are indistinguishable from high precision ones in cross-sections. Our calculations agree with the currently available measurement within 7%, i.e., well beyond the precision requirements.

Our proof-of-concept introduces a computationally affordable way to compute full-dimensional interaction potentials and scattering quantum dynamics with a precision sufficient to reduce the model-limited biases originating from the pressure broadening and thus support instrument-limited science with JWST and future missions.

Laurent Wiesenfeld, Prajwal Niraula, Julien de Wit, Nejmeddine Jaïdane, Iouli E. Gordon, Robert J. Hargreaves

Comments: Submitted to ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Atomic Physics (physics.atom-ph)
Cite as: arXiv:2409.04439 [astro-ph.EP] (or arXiv:2409.04439v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.04439
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Submission history
From: Prajwal Niraula
[v1] Fri, 6 Sep 2024 17:58:16 UTC (1,165 KB)
https://arxiv.org/abs/2409.04439
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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