Mass Spectrometric Fingerprints of Organic Compounds in Sulfate-Rich Ice Grains: Implications for Europa Clipper
Maryse Napoleoni, Fabian Klenner, Lucía Hortal Sánchez, Nozair Khawaja, Jon K. Hillier, Murthy S. Gudipati, K. P. Hand, S. Kempf, Frank Postberg
Abstract
The surface ice of Europa is known to contain high proportions of inorganic material that could heavily influence the compositional analysis of organic compounds in ejecta ice grains by the SUrface Dust Analyzer (SUDA) impact ionization mass spectrometer onboard NASA’s Europa Clipper mission. We previously have analyzed the effects of NaCl on the mass spectral appearance of organic-rich ice grains. Here, we present analogue experiments for SUDA simulating cation and anion mass spectra of organic-rich ice grains together with sulfates, one of the most abundant inorganic compounds on Europa’s surface. Using the Laser Induced Liquid Beam Ion Desorption (LILBID) technique, a diverse range of representative organic species in MgSO 4 - and H 2 SO 4 -rich matrices at concentrations ranging from 0.01 to 1 M were measured. Results show that mass spectrometric signatures of organic species can be detected in MgSO 4 -rich and H 2 SO 4 -rich ice grains via molecular ions, although the mass spectral appearance changes from molecular ions to a range of adducts with Mg 2+, OH –, and HSO 4 – ions and MgSO 4 and H 2 SO 4 molecules depending on the matrix and the matrix concentration. Sensitivity to the organics is typically higher in cation mode than in anion mode in both matrices. Due to suppression effects, the sensitivity to detect the organics decreases with increasing MgSO 4 concentration, but it does not decrease in H 2 SO 4 matrices in cation mode. We establish generic rules for the detection of organics in Europan ice grains by SUDA, applicable to a wide range of organic species in complex ice matrices. The recorded mass spectra complement a spectral reference database for Europa Clipper and other ocean world missions.