Revealing Callisto’s Carbon-rich Surface And CO2 Atmosphere With JWST

By Keith Cowing
Status Report
January 31, 2024
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Revealing Callisto’s Carbon-rich Surface And CO2 Atmosphere With JWST
JWST/NIRSpec integrated spectra and 1σ uncertainties (gray error bars) of Callisto’s leading (purple) and trailing (red) hemisphere, normalized to 1 at 3.82 μm and offset vertically for clarity. The G395H grating has a ~0.1 μm wide wavelength gap, shifting between ~4 and 4.2 μm across NIRSpec IFU’s 29 image slices. Some of the image slices that span Callisto’s disk include wavelength coverage between ~4 and 4.2 μm, which are shown here for Callisto’s leading (bright blue) and trailing (bright orange) hemispheres. All spectral features identified in this study are labeled, with dotted lines indicating their central wavelengths. Features with confirmed compositions have bolded labels, whereas weak features, or those with multiple compositional interpretations, are italicized and followed by question marks. Possible bands and spectral structure at wavelength >4.98 μm may result from data calibration artifacts and are not analyzed in this study. The inset box shows a close-up of the 4.19 to 4.42 μm wavelength range, highlighting the CO2 features we have identified and the different band centers for 12CO2 on Callisto’s leading (4.254 μm) and trailing (4.250 μm) hemisphere, as well as a feature near 4.3 μm that may result from an isotope of CO2 or could be a residual solar line (Appendix A.3). — astro-ph.EP

We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope.

These spatially resolved data show strong 4.25-micron absorption bands resulting from solid-state 12CO2, with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H2O mixed with carbonaceous compounds. We detected CO2 rovibrational emission lines between 4.2 and 4.3 microns over both hemispheres, confirming the global presence of CO2 gas in Callisto’s tenuous atmosphere.

These results represent the first detection of CO2 gas over Callisto’s trailing side. The distribution of CO2 gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38-micron absorption band that likely results from solid-state 13CO2. A prominent 4.57-micron absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike 12CO2, suggesting these two spectral features are spatially anti-associated.

The distribution of the 4.57-micron band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide (OCS), and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface-atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.

Richard J. Cartwright, Geronimo L. Villanueva, Bryan J. Holler, Maria Camarca, Sara Faggi, Marc Neveu, Lorenz Roth, Ujjwal Raut, Christopher R. Glein, Julie C. Castillo-Rogez, Michael J. Malaska, Dominique Bockelee-Morvan, Tom A. Nordheim, Kevin P. Hand, Giovanni Strazzulla, Yvonne J. Pendleton, Katherine de Kleer, Chloe B. Beddingfield, Imke de Pater, Dale P. Cruikshank, Silvia Protopapa

Comments: Accepted in AAS Planetary Science Journal, January 2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2401.17236 [astro-ph.EP] (or arXiv:2401.17236v1 [astro-ph.EP] for this version)
Submission history
From: Richard Cartwright
[v1] Tue, 30 Jan 2024 18:25:05 UTC (15,983 KB)

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) 🖖🏻