Detection of organic compounds in freshly ejected ice grains from Enceladus’s ocean

Nozair Khawaja, Frank Postberg, Thomas R. O’Sullivan, Maryse Napoleoni, Sascha Kempf, Fabian Klenner, Yasuhito Sekine, Maxwell Craddock, Jon Hillier, Jonas Simolka, Lucía Hortal Sánchez, Ralf Srama

Nature Astronomy10/1/2025·DOI·Read paper

Abstract

Abstract Saturn’s moon Enceladus ejects a plume of ice grains and gases originating from a subsurface ocean via fractures near its south pole. The chemical characterization of organic material in such ice grains was previously conducted via the analysis of mass spectra obtained in Saturn’s E ring by Cassini’s Cosmic Dust Analyzer at impact speeds below 12 km s −1 . Here we present a comprehensive chemical analysis of organic-bearing ice grains sampled directly from the plume during a Cassini fly-by of Enceladus (E5) at an encounter speed of nearly 18 km s −1 . We again detect aryl and oxygen moieties in these fresh ice grains, as previously identified in older E-ring grains. Furthermore, the unprecedented high encounter speed revealed previously unobserved molecular fragments in Cosmic Dust Analyzer spectra, allowing the identification of aliphatic, (hetero)cyclic ester/alkenes, ethers/ethyl and, tentatively, N- and O-bearing compounds. These freshly ejected species are derived from the Enceladus subsurface, hinting at a hydrothermal origin and involvement in geochemical pathways towards the synthesis and evolution of organics.

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