2025/12/22 by Jun Takeshita, Yuichiro Cho, Y H Cho +10 · 1 voice
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Planetary Science and Exploration
paper · doi:10.3847/psj/ae548e
openalex publication_date 2026/04/01 · openalex created_date 2026/04/28 · openalex updated_date 2026/06/11
Abstract Enceladus may host a subsurface ocean with biologically relevant chemistry. Plumes released from this ocean preserve information on its chemical state, and previous analyses suggest weakly to strongly alkaline pH. Constraining the ocean’s pH is critical for assessing its habitability, as pH governs the chemical energy available for potential life. This requires identifying pH-sensitive minerals in plume deposits. Raman spectrometers, which have recently been incorporated into flight instruments, offer a potential approach for mineral identification on icy moons. However, their applicability to pH estimation from plume-derived minerals has not been investigated. We evaluate whether Raman measurements of plume particles deposited on the surface of Enceladus can distinguish between weakly and strongly alkaline ocean models. Fluids with pH values of 9 and 11 were frozen under vacuum conditions analogous to those on Enceladus. The resulting salt deposits were then analyzed using a Raman system designed to simulate the SuperCam instrument for Mars, featuring a pulsed laser, standoff geometry, and a spectral resolution coarser than 10 cm −1 . The obtained Raman spectra showed diagnostic peaks for pH-dependent carbonate precipitation: at pH 9, signals consistent with NaHCO 3 (673, 1045, and 1267 cm −1 ) and Na 2 CO 3 (1081 cm −1 ) were detected, whereas only Na 2 CO 3 was observed at pH 11. These findings demonstrate that flight-like Raman spectrometers can distinguish these key mineral phases without high-resolution laboratory optics. This result validates that in situ Raman spectroscopy is a practical approach to constrain the pH of the subsurface ocean, a key parameter for assessing its chemical evolution and potential habitability.