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Mass Spectrometric Fingerprints of Organic Compounds in Salt-Rich Ice Grains: Implications for Europa Clipper

Presentation #114.05 in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Mass Spectrometric Fingerprints of Organic Compounds in Salt-Rich Ice Grains: Implications for Europa Clipper

The SUrface Dust Analyzer (SUDA) - Europa Clipper’s impact ionization mass spectrometer - will analyse ice grains ejected from the surface due to micrometeorite impacts1 or in putative plumes2. Calibration of SUDA can be done using Laser Induced Liquid Beam Ion Desorption (LILBID) to reproduce SUDA mass spectra. LILBID experiments have shown that bioessential organic molecules3,4 and biosignatures5 could be identified in water ice spectra produced by SUDA-type instruments.

The detection of organics by SUDA might be complicated by suppression effects and interferences due to salts and acids, which are abundant in Europa’s surface and strongly influence spectral results. We simulated the mass spectra of ejecta ice grains rich in both organic and inorganic substances, to evaluate the detectability and mass spectrometric fingerprints of organics in matrices of typical Europa composition. We measured the LILBID mass spectra of 7 organic species (5-amino-1-pentanol, acetic acid, benzoic acid, butylamine, glucose, methanol, pyridine) at concentrations ranging from 1 to 5 wt% and in matrices composed of 0.01M to 1M NaCl, MgSO4 or H2SO4.

We determined the matrix effects in both ion modes. Results show that the organic species can be detected in ice grains via molecular ions and a range of adducts with Na+, Cl-, Mg2+, OH-, HSO4- ions, and NaCl, NaOH, MgSO4 and H2SO4 molecules. The sensitivity to the organics strongly depends on the organic’s properties (e.g., functional groups) and is typically higher in cation mode than anion mode. Due to salt-related suppression effects, the sensitivity to the organics decreases by 1 to 2 orders of magnitude with increasing salt concentration. Suppression effects strongly depend on the ion mode, the matrix and the organic species. The lack of suppression effects for organics in H2SO4 matrices in cation mode suggests a better sensitivity in sulfuric acid-rich regions of Europa.

Rules were established to predict the spectral fingerprints of different organic families in Europan ice grains6. We confirm the need for SUDA to have both ion modes to identify of a wide range of organics. Analogue LILBID spectra will help determine the concentrations of both organic and inorganic constituents in the surface ice of Europa and complement a reference database for Europa Clipper.

1Krivov et al. 2003 Planet. Space Sci. 51(3):251269 2Roth et al. 2014 Science 343:171–174 3Klenner et al. 2020a Astrobiology 20:179–189 4Klenner et al. 2020b Astrobiology 20:1168–1184 5Dannenmann et al. 2023 Astrobiology 23:1, 60–75 6Napoleoni et al. 2023 ACS Earth Space Chem 7(4), 735-752

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