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Comprehensive spectroscopy of Enceladus and Europa with JWST

Presentation #401.05 in the session JWST Views of the Outer Planets and their Moons (Oral Presentation)

Published onOct 23, 2023
Comprehensive spectroscopy of Enceladus and Europa with JWST

Enceladus and Europa are prime targets in the search for life and habitable conditions in our solar system, and the James Webb Space Telescope (JWST) has now provided unprecedented views of these ocean worlds using spectroscopic observations.

At Enceladus, we directly sampled the fluorescence emissions of water [H2O] vapor with the JWST’s NIRSpec instrument that revealed an extraordinarily extensive plume (up to 10,000 km, or 40 times Enceladus’ radius) at cryogenic temperatures (25 K), embedded in a large bath of emission originating from Enceladus’ torus. The observed outgassing rate (300 kg/s) is similar to that derived from close-up observations with Cassini almost two decades ago, and the torus density is consistent with previous spatially unresolved measurements acquired with Herschel around a decade ago, suggesting that the vigor of gas eruption from Enceladus has been relatively stable over decadal timescales. We performed sensitive searches for several non-water species (carbon dioxide [CO2], carbon monoxide [CO], methane [CH4], ethane [C2H6], methanol [CH3OH]), but none were identified in the coma. On the surface of the trailing hemisphere, we observed strong H2O ice features, including its crystalline form, yet we did not detect CO2, CO, or ammonia [NH3] ice signatures from these observations.

For Europa, we mapped it with JWST’s NIRSpec and MIRI IFUs (Integral Field Units) in search of active sources across its atmosphere and surface. Our sensitive search for gas plumes revealed no detection of H2O, CO2, CH3OH, C2H6, nor CH4 gas emissions. Across its surface and particularly at Tara Regio, a complex CO2 mixture was discovered, recovering four distinct CO2 ice features, and the first detection of isotopic 13CO2 absorption on an ocean-bearing moon in the outer Solar System. These observations, coupled with the non-detection of an active plume, point to a new endogenous source for carbon on this ocean world. This finding, when combined with the measured isotopic ratio, has significant implications for Europa’s subsurface carbon chemistry and habitability.

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