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Laboratory Investigation of Hydrothermally Processed Triglycine: Implications for Organic Enriched Enceladean Ice Grains

Presentation #313.01 in the session Enceladus (Poster)

Published onOct 23, 2023
Laboratory Investigation of Hydrothermally Processed Triglycine: Implications for Organic Enriched Enceladean Ice Grains

Mass spectrometers onboard the Cassini spacecraft – the Cosmic Dust Analyzer and the Ion and Neutral Mass Spectrometer — provided evidence for water-rock interactions and hydrothermal (HT) reactions at the ocean-floor of Enceladus1,2. A diverse range of organic material containing various moieties (N-, O- and aryl groups), were identified in ice grains ejected from Enceladus’ south pole, alongside high mass fragments (mass > 200) and low mass (mass < 100) prebiotically relevant compounds3,4.

The latter soluble and reactive low-mass compounds could provide building blocks for amino acid (AA) synthesis under Enceladus hydrothermal conditions (EHTC). AAs play a distinct role in the origins of life on Earth - both as monomers and peptides - and are key biosignatures for the identification of extraterrestrial life. Therefore, it is of great importance to investigate hydrothermal processing (HTP) of AAs and peptides under EHTC. Here, we process a simple tripeptide of glycine relevant for astrobiology investigations. Previous works have revealed triglycine (GGG) formation is inhibited under conditions relevant to Enceladus’ HT system5. Thus, the detection of GGG and its degradation products in Enceladean ice grains may hint at biotic or hitherto unknown abiotic processes in its subsurface ocean.

We investigate the mass spectral appearance of GGG in ice grains after processing under EHTC (80 °C, 80 bar; [GGG]=0.005 M; 1:20 peridotite-water). A systematic methodology is adopted in order to assess degradation pathways of GGG during HTP. Different solutions were prepared and HT processed for 2 and 4 hours: 1) GGG 2) GGG + Enceladus ocean simulant (EOS; pH=9, [NaCl]=0.1 M), 3) GGG + minerals, 4) GGG + EOS + minerals.

Processed and unprocessed HT samples, were measured using laser-induced liquid beam ion desorption (LILBID), which accurately simulates hypervelocity impact ionization mass spectra of ice grains6. We identified partial degradation of GGG in HT processed solutions 1 and 2, while 3 and 4 showed no signs of degradation. Solutions 1 and 2 exhibit spectral differences hinting that NaCl affects the degradation pathway of GGG. Lack of evidence for HTP in spectra of solutions 3 and 4 might indicate the mineral used fulfils a preservative role.

1 Hsu et al. 2015 Nature 519, 207–210

2 Waite et al. 2017 Science 356, 155-159

3 Khawaja et al. 2019 MNRAS 489 (4) 5231–5243.

4 Postberg & Khawaja et al. 2018 Nature 558, 564–568.

5 Takahagi et al. 2019 ACS Earth Space Chem. 2019, 3, 11, 2559–2568.

6 Klenner et al. 2019 RCM vol. 33,22

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