Detecting Complex Biomolecules at the Plume of Enceladus Using Fluorescence Spectroscopy

We present a proposal for a conceptually new type of life detection mission for the outer Solar System. Using preliminary radiative transfer calculations, we show that a small spacecraft with a UV laser and fluorescence spectrometer could detect the distinctive signal of aromatic amino acids – particularly tryptophan. Tryptophan, a complex amino acid essential to proteins in Earth-life, fluoresces strongly when excited at UV wavelengths. Though Enceladus’ ocean sits beneath a layer of ice, it is possible to gain insight into its contents by observing the south polar plumes, which spew water vapor from the ocean to the surface. A spacecraft equipped with a UV laser and spectrograph could observe the fluorescence of tryptophan in and around the plume of Enceladus during a fly-by, and therefore confirm the presence of complex biomolecules. We assess the viability of this detection method for plausible fly-by mission scenarios using back of the envelope radiative transfer calculations, which seek to identify limitations on the laser power, distance, and tryptophan concentration required for detection in plume vapor and the surrounding surface snow-pack material.