Comets and Asteroids

JWST Reveals Anomalously Enhanced Methane Outgassing From Below Chiron’s Water Ice And Carbon Dioxide Bearing Surface

By Keith Cowing
Status Report
astro-ph.EP
May 26, 2026
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JWST Reveals Anomalously Enhanced Methane Outgassing From Below Chiron’s Water Ice And Carbon Dioxide Bearing Surface
Spectral characterization of Chiron’s surface composition. a Comparison of the bestfit spectral model of the surface composition (red) with the measured spectrum (black). The surface is best described by an intimate mixture of water ice in both amorphous and crystalline phases, carbon dioxide ice, and tholin-like materials. b Residuals between the model and the data show an excellent fit, with a root mean square deviation that is just 1% higher than the average scatter in the data. c Zoomed-in view of the complex organic absorption feature spanning 3.3–3.6 µm, with the individual component bands indicated by dashed lines. Comparison between the measured spectrum and synthetic spectra of several candidate species, convolved to the spectral resolution of the data, points to C3H8 and/or ice tholins produced by the irradiation of H2O ice and C2H6 as the most plausible candidates for the observed organic feature. — astro-ph.EP

Centaurs are inward-scattered Kuiper belt objects, with some exhibiting comet-like activity. The physical mechanisms powering this activity remain poorly understood, with carbon monoxide (CO) sublimation or the crystallization of amorphous water ice commonly invoked as the dominant drivers.

Here we present high-resolution JWST spectroscopy of 2060 Chiron, one of the largest known Centaurs, revealing methane and carbon dioxide gas emission with distinct coma spatial morphologies and production rates of QCH4=(1.55±0.04)×1027 molecules s−1 and QCO2=(1.01±0.06)×1026 molecules s−1.

The surface spectrum displays spectral signatures attributed to water ice, carbon dioxide, CO, and refractory organic-rich material, while lacking detectable methane ice absorption bands. These findings suggest that carbon dioxide production is sustained by direct surface sublimation, whereas methane originates from the subsurface.

The absence of measurable CO emission despite the presence of solid-state CO implies that any surviving primordial CO reservoir remains thermally inaccessible at greater depth below the methane, while irradiation-produced near-surface CO may be inefficiently released from the surface matrix. This inferred volatile stratification may result from long-term thermal evolution or potentially partial differentiation.

Chiron differs markedly from other active small bodies, where CO production typically dominates over methane, indicating that Centaur activity may be driven by a broader range of volatile and thermophysical processes than predicted by canonical models.

Ian Wong, Silvia Protopapa, Aurélie Guilbert-Lepoutre, Geronimo L. Villanueva, Bryan Holler, Rosario Brunetto, Joshua P. Emery, Noemí Pinilla-Alonso, Ana Carolina de Souza Feliciano, Estela Fernández-Valenzuela

Comments: 30 pages, 7 figures, submitted to journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2605.23038 [astro-ph.EP] (or arXiv:2605.23038v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2605.23038
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Submission history
From: Ian Wong
[v1] Thu, 21 May 2026 21:05:41 UTC (2,187 KB)
https://arxiv.org/abs/2605.23038

Astrobiology, Astrochemistry,

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 🖖🏻

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