JWST molecular mapping and characterization of Enceladus' water plume feeding its torus

TL;DR

Using JWST's NIRSpec instrument, this study maps and characterizes Enceladus' water plume and its torus, revealing stable activity, extensive outgassing, and the absence of other detected gases, supporting future icy body exploration.

Contribution

First JWST-based detailed mapping of Enceladus' water plume and torus, demonstrating stable activity and providing insights into its composition and structure.

Findings

Plume extends up to 10,000 km at 25 K

Outgassing rate of 300 kg/s consistent with past measurements

No detection of non-water gases like CO2, CO, CH4

Abstract

Enceladus is a prime target in the search for life in our solar system, having an active plume likely connected to a large liquid water subsurface ocean. Using the sensitive NIRSpec instrument onboard JWST, we searched for organic compounds and characterized the plume's composition and structure. The observations directly sample the fluorescence emissions of H2O and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus' torus. Intriguingly, the observed outgassing rate (300 kg/s) is similar to that derived from close-up observations with Cassini 15 years ago, and the torus density is consistent with previous spatially unresolved measurements with Herschel 13 years ago, suggesting that the vigor of gas eruption from Enceladus has been relatively stable over decadal timescales. This level of activity is sufficient to maintain a derived column density of 4.5x1017 m-2 for the embedding equatorial torus, and establishes Enceladus as the prime source of water across the Saturnian system. We performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice features, including its crystalline form, yet we do not recover CO2, CO nor NH3 ice signatures from these observations. As we prepare to send new spacecraft into the outer solar system, these observations demonstrate the unique ability of JWST in providing critical support to the exploration of distant icy bodies and cryovolcanic plumes.