Enceladus plumes may reveal pH clues about its subsurface ocean.

A Japanese study used laboratory simulations of frozen plume deposits and Raman spectroscopy to identify carbonate minerals and distinguish pH differences, suggesting the method may be used to estimate the alkalinity of Enceladus' subsurface ocean.

Scientists from Japan tested whether Raman spectroscopy can be used to estimate the pH of Enceladus' subsurface ocean by analyzing plume deposits on the moon's surface. The team ran laboratory experiments that simulated salty plume fluid evaporating in vacuum and then freezing, leaving salt and carbonate residues. Raman instruments were configured to mimic how they would operate on a space mission and were used to detect carbonate minerals in those residues. Cassini's earlier flybys revealed plumes from Enceladus' south pole that contain water, salts, organics, hydrogen and heat, which motivates efforts to learn more about the moon's ocean. Key findings: - The researchers prepared carbonate-rich salty fluid samples at different pH values and evaporated them in a vacuum chamber to leave salt deposits that were then frozen. - Raman spectroscopy instruments were configured to simulate spaceflight operation and were used to analyze the simulated surface deposits. - The instruments could identify carbonate minerals in the salt residues and distinguish differences consistent with weak to strong alkaline pH ranges reported for the plumes (about pH 8–12). - The study notes Raman spectroscopy has flight heritage, citing instruments such as SuperCam and SHERLOC on Perseverance and planned Raman instruments on ESA's ExoMars Rosalind Franklin and JAXA's MMX mission. - The authors conclude that in situ Raman observations of surface carbonates may enable qualitative estimates of the subsurface ocean pH. Summary: These laboratory results show Raman spectroscopy can detect carbonate minerals in simulated Enceladus plume deposits and can differentiate pH-related signatures in those salts. Undetermined at this time.