Macromolecular Organic‑Rich Ice Grains in Enceladus Plume and E Ring Reveal Core–Shell Grains with Large Organic Signatures

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Large, organic-rich ice grains were detected in Enceladus’s plume and the E ring, containing macromolecular organics heavier than 200 atomic mass units with a repeating ~12.5 u mass pattern and benzene-derived cations around 77–79 u, plus tropylium near 91 u, embedded in water ice with little salt as 0.2–2 μm core-shell grains, implying an Enceladus origin from a thin organic layer at the ocean-water table dispersed by bubble bursting and recondensing as ice-coated grains, with INMS fragmentation products including CO, H2CO, CH3OH and possibly C2H3N supporting larger organic components rather than gas-phase species, and suggesting formation from primordial insoluble organic matter or hydrothermal processing in Enceladus’s ocean with oxygen and nitrogen heteroatoms, benzene-ring substructures, and methane present.