Exploring Ocean Worlds with Combined Raman and Infrared Spectroscopy: Spectroscopic Laboratory Analysis of Europa Relevant Simulant Samples

Abstract:

Analyses from the past few decades of outer Solar System satellites reveal the potential habitability of Jupiter and Saturn’s icy moons. While the Galileo spacecraft collected many initial measurements of the Jupiter satellites that include images of surface characteristics and the detection of induced magnetic fields that give rise to the theory that these icy moons foster a liquid ocean underneath the outer icy shell [1], this data set is not sufficient to determine habitability and further exploration is required. Combined infrared and Raman spectroscopy provide unique complementary capabilities for the detection and characterization of materials of high astrobiological potential, including organic compounds and minerals that may host biosignatures.

Spectra in the near-infrared exhibit unique signatures of organics, salts, acid hydrates, water ice phases, altered silicates, and radiolytic compounds and are useful for identification of material composition on the top few microns of a planetary surface. Observations in this spectral region can be done at greater distances from the surface, and results can be used to target sites of interest for further analysis. Raman spectroscopy possesses unique capabilities for detection and characterization of substances such as water, amino acids, organics, sulfates, nitrates, oxides, hydrous minerals and several other molecules indicative of life at ranges of 5-10 meters, with the ability to penetrate centimeters into clean ice and enable depth measurements below the surface inaccessible to infrared analysis.

Europa relevant samples were produced and measured by an infrared spectrometer and a compact standoff Raman spectrometer under cryogenic conditions. The infrared system was able to detect and discriminate between Ocean World relevant sample simulants of frozen hydrocarbons and brines. Additionally, the Raman system was able to detect and discriminate between frozen brines, hydrous minerals, and amino acid solutions, showing that both are complementary techniques for a mission to an Ocean World.

[1] J. Kimura and N. Kitadai (2015) Astrobiology, 15.