Mass Spectral Properties of Hydrothermally Processed Triglycine (GGG) in Ice Grains Emitted by Enceladus and Europa
Authors: Khawaja Nozair , Hortal Sánchez Lucía , O’Sullivan Thomas , Bloema Judith , Napoleoni Maryse , Klenner Fabian , Beinlich Andreas , Hillier Jon , Srama Ralf , Postberg Frank 
Published: March 2024

The Cassini-Huygens space mission provided evidence for a global subsurface ocean [1] and ongoing hydrothermal activity within Enceladus, inferred primarily from the presence of silica (SiO2) nanoparticles and molecular hydrogen expelled from the depths of subsurface ocean [2,3]. The ocean material expelled from the south pole of Enceladus was sampled by Cassini&#8217;s mass spectrometers - ice grains were sampled by the Cosmic Dust Analyzer (CDA) whilst gases were sampled by the Ion and Neutral Mass Spectrometer (INMS). Enceladus hosts a variety of organic molecules, spanning a range of chemical properties. Postberg et al. [4] observed mass spectral signatures related to complex high-mass (> 200 u) refractory insoluble organic material in organic-containing ice grains. In a concurrent study, low-mass (< 100 u) volatile organics with oxygen-, nitrogen-, and aromatic moieties were also identified in the emitted ice grains [5].
Hydrothermal experiments are common in studies of the early and modern Earth, and exploration of terrestrial hydrothermal environments has yielded rich scientific return. Laboratory simulations of Enceladus&#8217;s subsurface chemistry [6,7] have thus far not considered how hydrothermally processed material would appear in impact ionization mass spectra, and therefore need to include measurements with analogue techniques for spaceborne instruments, such as laser-induced liquid beam ion desorption (LILBID). LILBID has been shown to accurately simulate the mass spectra produced by hypervelocity impacts of ice grains onto impact ionization mass spectrometers [8].
With a newly established hydrothermal facility at Freie Universit&#228;t Berlin, we simulate hydrothermal conditions in the depths of Enceladus&#8217;s ocean and investigate the hydrothermal processing of triglycine (GGG; 9]. The hydrothermal setup is capable of operating at pressures of up to ~ 150 bar and temperatures of up to 150 &#176;C, and supports sampling during the experiment. Here, for the first time, the extracted samples are measured using LILBID. The first investigation with this new experimental setup assesses the decomposition of triglycine peptide (GGG) at elevated temperature and pressure. It is a simple, well-studied peptide and scientifically valuable option for early experiments and calibration of the hydrothermal apparatus. 0.005 M solutions of GGG were processed at a pressure of 80 bar and a temperature of 80 &#176;C, which lies within the range of conditions suggested for the alkaline (pH 8.5-10.5) hydrothermal systems of Enceladus. After 2 and 4 hours of hydrothermal processing, samples were extracted and measured using the LILBID facility. Here we present LILBID spectra of both hydrothermally processed and unprocessed material, showing their fragmentation pathways. These results will provide guidelines for biosignatures with a future Enceladus mission and also to the SUrface Dust Analyzer (SUDA), an impact ionization instrument onboard Europa Clipper.
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