Collecting amino acids in the Enceladus plume

Abstract

We numerically model the dynamics of the Enceladus plume ice grains and define our nominal plume model as having a particle size distribution n(R) ~ R−q with q = 4 and a total particulate mass rate of 16 kg s−1. This mass rate is based on average plume brightness observed by Cassini across a range of orbital positions. The model predicts sample volumes of ~1600 µg for a 1 m2 collector on a spacecraft making flybys at 20–60 km altitudes above the Enceladus surface. We develop two scenarios to predict the concentration of amino acids in the plume based on these assumed sample volumes. We specifically consider Glycine, Serine, α-Alanine, α-Aminoisobutyric acid and Isovaline. The first ‘abiotic’ model assumes that Enceladus has the composition of a comet and finds abundances between 2 × 10−6 to 0.003 µg for dissolved free amino acids and 2 × 10−5 to 0.3 µg for particulate amino acids. The second ‘biotic’ model assumes that the water of Enceladus's ocean has the same amino acid composition as the deep ocean water on Earth. We compute the expected captured mass of amino acids such as Glycine, Serine, and α-Alanine in the ‘biotic’ model to be between 1 × 10−5 to 2 × 10−5 µg for dissolved free amino acids and dissolved combined amino acids and about 0.0002 µg for particulate amino acids. Both models consider enhancements due to bubble bursting. Expected captured mass of amino acids is calculated for a 1 m2 collector on a spacecraft making flybys with a closest approach of 20 km during mean plume activity for the given nominal particle size distribution.

Returning Samples From Enceladus for Life Detection

“…The traded quantities are mission duration, v (fuel mass, cost), and sampling velocity, whereas sampling altitude is set by navigation uncertainty in all cases. A sampling altitude typically considered is 50 km (e.g., Guzman et al, 2019), low enough that the plume density is high, yet high enough that material from the multiple venting locations at the surface have merged into a single plume.…”

Key Technologies and Instrumentation for Subsurface Exploration of Ocean Worlds

“…For plume-sampling, it is advantageous that the number density of ice grains and their average size both increase closer to the surface (Hedman et al 2009;Postberg et al 2011b;Southworth et al 2019;, so that a close flyby would drastically increase the collectable mass of ice grains. However, even optimistic calculations predict a sample mass of 1.6 mg (or 1.6 mL) per m 2 collector area at a single low-altitude flyby (25 km) over the most active part of Enceladus' SPT (Guzman et al 2019). This material will contain on average less than 0.5% of organic material in total (Postberg et al 2018a), so that even under optimal circumstances, less than 10 µg of organic material would be sampled per m 2 of collector area and per flyby.…”

Membrane Lipid Composition and Amino Acid Excretion Patterns of Methanothermococcus okinawensis Grown in the Presence of Inhibitors Detected in the Enceladian Plume

“…The latter, however, may not be applicable in the Enceladian ocean, as racemization timescales are short compared to production timescales [83,84]. An alternative approach would be to determine the relative abundance of the detected amino acids to Gly or other prebiotic amino acids, as biosynthetic processes can cause a higher abundance of complex amino acids to optimize protein function and stability [88,89]. Another approach may be the search for specific groups in the side chains of amino acids as biomarkers that are characterized by the highest propensities related to terrestrial life [90].…”