Fluid inclusions establish natron as a key astrobiological target on Enceladus

Abstract Saturn’s moon Enceladus is a priority target for both NASA Flagship and ESA Large-class (L4) 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 observation of fluid inclusions in cryogenic natron (Na 2 CO 3 .10H 2 O), a mineral predicted to occur both 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 natron at the surface and that direct sampling should prioritise fresh plume deposits where natron is abundant due to its potential to trap and preserve signatures of life.