Decomposition of Amino Acids in Water with Application to In-Situ Measurements of Enceladus, Europa and Other Hydrothermally Active Icy Ocean Worlds

Abstract

To test the potential of using amino acid abundances as a biosignature at icy ocean worlds, we investigate whether primordial amino acids (accreted or formed by early aqueous processes) could persist until the present time. By examining the decomposition kinetics of amino acids in aqueous solution based on existing laboratory rate data, we find that all fourteen proteinogenic amino acids considered in this study decompose to a very large extent (>99.9%) over relatively short lengths of time in hydrothermally active oceans. Therefore, as a rule of thumb, we suggest that if amino acids are detected at Enceladus, Europa, or other hydrothermally active ocean worlds above a concentration of 1 nM, they should have been formed recently and not be relicts of early processes. In particular, the detection of aspartic acid (Asp) and threonine (Thr) would strongly suggest active production within the ocean, as these amino acids cannot persist beyond 1 billion years even at the freezing point temperature of 273K. Identifying amino acids from the oceans of icy worlds can provide key insight into their history of organic chemistry.

Solid-State Single-Molecule Sensing with the Electronic Life-detection Instrument for Enceladus/Europa (ELIE)

“…The discovery of Enceladus' plume of icy grains and gas by the Cassini mission (Porco et al 2006;Waite Jr et al 2009) and the tentative evidence for transient water vapor plumes at several locations on Europa found in Hubble Space Telescope observations (Roth et al 2014;Sparks et al 2016), support the idea of material transport from the interior of these moons and, in concert with other studies, the presence of global subsurface oceans (Kivelson et al 2000;Thomas et al 2016;Zimmer et al 2000). Based on known amino acids degradation rates, previous works suggest that a detection of amino acids in these predicted subsurface oceans above a concentration of 1 nM would indicate active production by geochemical or biotic pathways (Truong et al 2019). Additionally, Steel et al 2017 predict that methanogen-based microbial life and abiotic hydrothermal processes could produce a maximum of 90 µM and 104 µM concentrations of amino acids, respectively, in the predicted subsurface oceans of these moons.…”

“…2000). Based on known amino acids degradation rates, previous works suggest that a detection of amino acids in these predicted subsurface oceans above a concentration of 1 nM would indicate active production by geochemical or biotic pathways (Truong et al . 2019).…”

Mass Spectrometric Fingerprints of Bacteria and Archaea for Life Detection on Icy Moons

“…The specific lipid patterns observed in biological sources could be used as biomarkers especially as they remain stable over long periods of time (Georgiou and Deamer, 2014). Unlike other biomarkers such as amino acids and nucleobases (Truong et al, 2019), hydrocarbon lipid fragments are able to survive over billions of years unless they are subjected to temperature and pressure extremes (Brocks, 1999;Eigenbrode, 2008).…”

Understanding Hypervelocity Sampling of Biosignatures in Space Missions

“…The average ice Ih density was confirmed from the periodic cell to be q 0 = 0.916723 g/cc, which is consistent with the experimentally reported density for ice Ih, q exp = 0.917 g/cc (Atkins and de Paula, 2010). Arg was chosen as the guest molecule because of its relatively low v f on bare impacts (Table 2); Arg has also been invoked as an indicator of active or recent production in the Enceladus ocean, as it may not persist over geologic timescales (Truong et al, 2019). We use the anionic FIG.…”