Fluid inclusions in natron - a window into the interior of Enceladus

Saturn’s moon Enceladus is a priority target for both NASA Flagship and ESA L4 class missions, as it possesses the three essential ingredients for life: liquid water, a source of energy, and all essential (CHNOPS) elements. As Enceladus’s ice crust is geologically active, future missions must understand its habitability through the lens of cryogeochemistry; yet the phase behaviour of Enceladus-type solutions is poorly constrained. Here, we investigate the freezing behaviour of an Enceladus-type Na-Cl-CO ₃ solution using combined synchrotron X-ray computed microtomography and diffraction. We report the first observation of fluid inclusions in cryogenic natron (Na ₂ CO ₃ · 10 H ₂ O), a mineral predicted to be present on and within Enceladus. We show that natron precipitation traps and preserves pockets of parent fluid, providing a window into the geochemistry of Enceladus’s interior and establishing natron as a mineral of high astrobiological importance. Consequently, we argue that future missions must have the capability to identify surface natron and that direct sampling should prioritize these deposits for their potential to trap and preserve signatures of life.