Multi-Instrument Spectral Framework for Biosignature Detection in Enceladus' Plumes

Active plume emissions from icy moons provide direct access to subsurface ocean material (Porco et al., 2006), enabling compositional characterisation of potentially habitable environments. This work develops a multi-instrument framework for organic compound detection in Enceladus' plumes by integrating complementary Cassini VIMS, INMS, and CDA datasets across multiple flyby encounters.

VIMS provided spatially resolved infrared spectra of plume particles and surface deposits, characterising water ice properties, grain sizes, and spectral signatures of volatiles including CO₂ and organic compounds (Brown et al., 2006; Dhingra et al., 2017). INMS measured neutral gas composition through mass spectrometry, identifying species including ammonia, molecular hydrogen from serpentinisation, and radiogenic argon indicating water-rock interactions (Waite et al., 2009). CDA characterised solid ice grain composition through impact ionisation mass spectrometry, detecting high-molecular-weight organic compounds exceeding 200 Da beyond INMS instrumental limits (Postberg et al., 2009, 2018). Together, these instruments span complementary molecular weight regimes and physical phases.

Our framework processes VIMS cubes using background subtraction for high phase angle observations to isolate plume signals, whilst water ice crystallinity analysis constrains particle formation temperatures. INMS processing integrates mass channel data accounting for fragmentation patterns to reconstruct parent molecule abundances. Multi-flyby comparison across diverse encounter geometries reveals water dominance with high molecular diversity throughout the accessible mass range.

The combined detection of liquid water, diverse organic chemistry including complex macromolecular compounds, and chemical energy sources establishes Enceladus as a compelling astrobiology target potentially analogous to Earth's hydrothermal vent ecosystems. This framework enables direct transferability to Europa Clipper's SUDA instrument and future missions, providing a methodology for comprehensive ocean world characterisation.

Acknowledgments

This work was financially supported by LA/P/0056/2020 (IMS DOI https://doi.org/10.54499/LA/P/0056/2020) and CQE UID/00100/2025 (https://doi.org/10.54499/UID/00100/2025), UID/PRR/100/2025 (https://doi.org/10.54499/UID/PRR/00100/2025) and UID/PRR2/00100/2025 (https://doi.org/10.54499/UID/PRR2/00100/2025) funded by national funds through FCT/MECI (PIDDAC). The authors also acknowledge funding by the Portuguese Foundation for Science and Technology (FCT) through project UID/04434/2025, and project ORIGINS (2022.05284.PTDC).

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