Salt-rich ice particles, termed Type 3, are a major compositional group within Enceladus’ plume and Saturn’s E-ring, and are thought to represent frozen micron-sized aerosolized droplets of Enceladus’ salty subsurface ocean. Here, we present an analysis based on ≈1000 mass spectra of individual Type 3 E-ring ice grains recorded by Cassini’s Cosmic Dust Analyser revealing a large compositional diversity amongst these grains. We find at least five basic compositional subtypes dominated by either NaCl, NaHCO3/Na2CO3, Na2HPO4/Na3PO4, NaOH, KCl, or KOH. By conducting experiments and thermodynamic calculations, we show that salt separation in agreement with CDA observations occurs as a consequence of salt mineral precipitation only within droplet sizes >10 µm and freezing rates below 20 K/min. We suggest that oceanic spray forms with an average size of 100’s of µm entrained in a slow gas flow causing slow freezing and separation of salts. Subsequently they are accelerated to speeds >100 m/s in narrow ice vents where frequent wall collisions lead to much smaller fragments mostly containing a single type of salt, matching CDA observations. The gradual cooling of ocean droplets in combination with wall collisions determine the final size distribution and provide an efficient chemical separation of both inorganic and organic oceanic constituents into differently composed ice grains ejected into Enceladus’ plume.
