Investigating the Origin and State of Europa’s CO2 with Global Observations from JWST

The Galileo mission first detected CO₂ on Europa over 25 years ago [1, 2], and it remains the only known carbon-bearing species on the satellite. Since this discovery, the origin and physical state of the CO₂ have been important questions key to understanding any potential relationship between the CO₂ and Europa’s subsurface chemistry. Specifically, the source of the CO₂ could be endogenic (possibly from the subsurface ocean), exogenic, or radiolytically produced from endogenic or exogenic carbon-bearing surface materials. In addition, pure CO₂ ice is highly unstable at Europa’s surface temperatures, so the CO₂ must be trapped within other, so-far-unidentified surface materials [1,2,3].

 

Recently, a single Cycle 1 JWST NIRSPec observation of Europa’s leading hemisphere provided new detail of Europa’s CO₂ by 1) resolving the 2.7 μm ν₁+ν₃ combination band for the first time, 2) revealing that the ν₃ fundamental asymmetric stretch band near 4.26 μm exhibits a double-peaked minimum, and 3) finding an association with the large-scale chaos region Tara Regio [4,5]. This observation provided new clues to uncovering the still-unknown trapping mechanism(s) and host material(s) of the CO₂, and suggested that the CO₂ may have an endogenic origin. However, the observation was limited to the leading hemisphere, which limited the ability to investigate relationships to the widespread geologic terrain and radiation patterns across Europa’s variegated surface.

 

We present our analysis of the first full surface observations of Europa’s CO₂ with JWST NIRSpec. We investigate how the CO₂ band strengths and positions correspond to Europa’s geology, compositional components, and surface bombardment patterns. We find that all three CO₂ features are widespread (Figure 1) and that the CO₂ is enhanced in chaos regions on the leading, sub-Jovian, and anti-Jovian hemispheres (Figure 2). Conversely, the CO₂ is depleted on the trailing hemisphere, which may be related to particle bombardment from Jupiter’s magnetosphere. We will discuss how these global JWST observations constrain the origin of Europa’s CO₂, as well as its physical state, correlation with other species, and relationship to radiolytic processes.

Figure 1: The total band area of the ν₃ asymmetric stretch feature across Europa’s surface, with regions of disrupted surface terrain outlined in black [6]. The CO₂ correlates with the disrupted terrain on all but the trailing hemisphere, where CO₂ appears substantially depleted and could reflect the effects of particle bombardment from Jupiter’s magnetosphere. The correlation with the disrupted terrain on the rest of the surface suggests that the CO₂ reflects an endogenic carbon source.

Figure 2: Example spectra of the 2.7 μm ν₁+v₃ fundamental band and double-peaked ν₃ fundamental asymmetric stretch bands of disrupted surface terrain on each of Europa’s hemispheres. While all of the CO₂ signatures are widespread, their depths and shapes vary across the surface, providing clues to the mechanisms underlying the stability of the CO₂.

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[2] Carlson, R. W., Calvin, W. M., Dalton, J. B., et al. 2009, in Europa, ed. R. T. Pappalardo, W. B. McKinnon, & K. K. Khurana, 283

[3] Hibbitts, C. A., & Szanyi, J. 2007, Icarus, 191, 371, doi: 10.1016/j.icarus.2007.04.012

[4] Trumbo, S. K., & Brown, M. E. 2023, Science, 381, 1308, doi: 10.1126/science.adg4155

[5] Villanueva, G. L., Hammel, H. B., Milam, S. N., et al. 2023, Science, 381, 1305, doi: 10.1126/science.adg4270

[6] Leonard, E. J., Patthoff, A. D, Senske, D. A. 2024, USGS, 18, 3513, doi: 10.3133/sim3513