Icy Worlds

A JWST Study Of CO2 On The Satellites Of Saturn

By Keith Cowing

Status Report

astro-ph.EP

October 6, 2025

Filed under astrogeology, Dione, Enceladus, Hyperion, Iapetus, ice, JWST, Mimas, Phoebe, Rhea, Saturn, Solid state CO2, Spectroscopy, Tethys, Titan

A JWST Study Of CO2 On The Satellites Of Saturn — An average of the continuum-removed spectra of the leading and trailing hemispheres of Mimas and Tethys and the leading hemispheres of Dione and Rhea, in black, and of the trailing hemispheres of Dione and Rhea, in red. The lines at the bottom show measured wavelengths of CO2 in different states, including in pure crystalline form and trapped as clathrate in crystalline water ice (Oancea et al. 2012), trapped in amorphous ice (Sandford & Allamandola 1990; G´alvez et al. 2008) and physisorbed onto minerals (Hibbitts & Szanyi 2007), which can lead to a wide range of wavelengths. The shorter wavelength 4.2487 µm line associated with the darker hemispheres of Dione and Rhea appears to have no corresponding absorption in the 2.7 µm region. — astro-ph.EP

Solid state CO₂ has been detected throughout the outer solar system, even at temperatures where crystalline CO₂ is unstable, requiring that the CO₂ be trapped in a separate host material.

The Saturnian satellites provide an ideal laboratory for the study of this trapped CO₂, allowing us to examine objects with identical insolation, but with a range of environments, ice exposure, organic abundance, and formation locations.

Here, we present JWST spectra of 8 mid-sized satellites of Saturn, including Mimas, Enceladus, Tethys, Dione, and Rhea interior to Titan, and Hyperion, Iapetus, and Phoebe exterior. The ∼4.26 μm CO₂ ν3 band is detected on each satellite, and the ∼2.7 μm ν1+ν3 band is detected on all but Phoebe and the leading hemisphere of Iapetus. Based on the wavelength shifts of these bands, we find four separate types of trapped CO₂ on the satellites.

On the inner satellites, CO₂ appears trapped in amorphous ice sourced from Saturn’s E-ring, and a second component of CO₂ is associated with the dark material most prominent on the trailing hemispheres of Dione and Rhea. On the outer satellites, CO₂ appears to be produced by irradiation of organics on Phoebe, which are then transported to the dark leading hemisphere of Iapetus and onto the dark regions of Hyperion.

CO₂ is also trapped by water ice on the trailing hemisphere of Iapetus and on Hyperion. These observations point to the continued need for laboratory studies to better understand the sources and trapping mechanisms of CO₂ throughout the outer solar system.

Michael E. Brown, Samantha K. Trumbo, Matthew Belyakov, M. Ryleigh Davis, Ashma Pandaya

Comments: Planetary Science Journal, in press
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2506.19921 [astro-ph.EP] (or arXiv:2506.19921v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.19921
Focus to learn more
Submission history
From: Michael Brown
[v1] Tue, 24 Jun 2025 18:00:20 UTC (443 KB)
https://arxiv.org/abs/2506.19921
Astrobiology, Astrochemistry,

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) 🖖🏻

Follow on Twitter