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

TL;DR

This study assesses amino acid stability in hydrothermal oceans of icy worlds, finding most amino acids decompose rapidly, thus recent detection indicates ongoing biological or chemical activity.

Contribution

It provides a kinetic framework to interpret amino acid detections on icy ocean worlds, linking amino acid presence to recent formation or activity.

Findings

Amino acids decompose >99.9% over geological timescales in hydrothermal oceans.

Detection of amino acids above 1 nM suggests recent formation or active production.

Aspartic acid and threonine cannot persist beyond 1 billion years at 273K.

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.