A Next-Generation Exoplanet Atmospheric Retrieval Framework for Transmission Spectroscopy (NEXOTRANS): Comparative Characterization for WASP-39 b Using JWST NIRISS, NIRSpec PRISM, and MIRI Observations

The advent of JWST has marked a new era in exoplanetary atmospheric studies, offering higher-resolution data and greater precision across a broader spectral range than previous space-based telescopes.

Accurate analysis of these datasets requires advanced retrieval frameworks capable of navigating complex parameter spaces. We present NEXOTRANS, an atmospheric retrieval framework that integrates Bayesian inference using UltraNest/PyMultiNest with four machine learning algorithms: Random Forest, Gradient Boosting, K-Nearest Neighbor, and Stacking Regressor.

This hybrid approach enables a comparison between traditional Bayesian methods and computationally efficient machine learning techniques. Additionally, NEXOTRANS incorporates NEXOCHEM, a module for solving equilibrium chemistry. We applied NEXOTRANS to JWST observations of the Saturn-mass exoplanet WASP-39 b, spanning wavelengths from 0.6 microns to 12.0 microns using NIRISS, NIRSpec PRISM, and MIRI.

Four chemistry models-free, equilibrium, modified hybrid equilibrium, and modified equilibrium-offset chemistry-were explored to retrieve precise Volume Mixing Ratios (VMRs) for H₂O, CO₂, CO, H₂S, and SO₂. Absorption features in both NIRSpec PRISM and MIRI data constrained SO₂ log VMRs to values between -6.67 and -5.31 for all models except equilibrium chemistry.

High-altitude aerosols, including ZnS and MgSiO₃, were inferred, with constraints on their VMRs, particle sizes, and terminator coverage fractions, providing insights into cloud composition. For the best-fit modified hybrid equilibrium model, we derived super-solar elemental abundances of O/H = 7.94 (+0.18/-0.18) x solar, C/H = 10.96 (+0.42/-0.41) x solar, and S/H = 3.98 (+0.29/-0.35) x solar, along with a C/O ratio of 1.17 (+0.03/-0.03) x solar, demonstrating NEXOTRANS’s potential for atmospheric characterization in the JWST era and beyond.

Tonmoy Deka, Tasneem Basra Khan, Swastik Dewan, Priyankush Ghosh, Debayan Das, Liton Majumdar

Comments: Accepted for publication in the Astrophysical Journal; 37 Pages, 17 Figures & 5 Tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2504.18815 [astro-ph.EP] (or arXiv:2504.18815v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.18815
Focus to learn more
Submission history
From: Liton Majumdar
[v1] Sat, 26 Apr 2025 06:06:38 UTC (24,219 KB)
https://arxiv.org/abs/2504.18815
Astrobiology