Exoplanets, -moons, -comets

Detection Of CO, H2O, And OH In WASP-18b With JWST/NIRISS Using Direct-Extracted Spectra And Cross-Correlation

By Keith Cowing
Status Report
astro-ph.EP
June 2, 2026
Filed under , , , , , ,
Detection Of CO, H2O, And OH In WASP-18b With JWST/NIRISS Using Direct-Extracted Spectra And Cross-Correlation
The planetary direct-extracted spectrum extraction steps. Top left: The original stellar spectral matrix. The red dashed lines indicate T1 and T4, while the white dashed lines mark T2 and T3. Bottom left: The master stellar spectrum, derived by averaging all spectra within the eclipse phase (T23). Top right: The planetary residual flux matrix, obtained by dividing the original flux matrix by the master stellar spectrum. Bottom right: The final WASP-18b direct-extracted spectrum (black) and the Gaussian filtered spectrum (light blue). — astro-ph.EP

The James Webb Space Telescope (JWST) has revolutionized the characterization of exoplanetary atmospheres, offering unprecedented sensitivity to probe their chemical and physical properties.

Recently, a growing trend has emerged to obtain atmospheric information directly from pixel-level planetary spectra. In this work, we re-analyzed the WASP-18b NIRISS/SOSS dataset by employing a direct extraction method. This new method preserves the spectral information at the native instrumental resolution, thereby enabling the application of cross-correlation techniques and providing atmospheric retrievals with enhanced precision and richer information content.

With this methodology, we report detections of CO at 4.4σ significance, H2O at 3.4σ, and OH at 7.8σ, where CO and OH were previously unseen. Building on these unambiguous detections, our subsequent retrieval analysis significantly improves the constraints on atmospheric abundances.

Our results demonstrate that the cross-correlation technique effectively extracts molecular signals from medium-resolution JWST data, enhancing detection sensitivity. By revisiting JWST archival data with cross-correlation and retrieval analysis, we can achieve a more comprehensive survey of planetary atmospheric chemistry, thereby placing precise constraints on key parameters such as planetary metallicity and C/O ratio.

Qinglin Ouyang, Fei Yan, Shuo Liu, Boyue Guo, Guo Chen, Enric Pallé, Yuanheng Yang, Wei Wang, Meng Zhai, Qian Chen

Comments: Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2605.30871 [astro-ph.EP] (or arXiv:2605.30871v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.30871
Focus to learn more
Submission history
From: Qinglin Ouyang
[v1] Fri, 29 May 2026 05:50:57 UTC (4,660 KB)
https://arxiv.org/abs/2605.30871

Astrobiology, Exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

Follow on Twitter
MORE FROM Exoplanets, -moons, -comets