A Subcritical Water Extractor Prototype for Potential Astrobiology Spaceflight Missions

Abstract

A top-level NASA exploration goal is the search for signs of life beyond Earth. Molecular biosignatures can be sought via in situ organic chemical analyses of samples collected from planetary bodies. Current spaceflight-ready technologies lack the required sensitivity to perform these analyses on key polar organic species primarily due to the low efficiency of transferring these molecules from natural samples into chemical instrumentation. One promising approach to improve the liberation of these molecules from sample matrices prior to analysis is through the use of liquid extraction, in which organic molecules are dissolved in heated, pressurized water. This process has never been performed on a spaceflight mission. As part of instrument maturation efforts, we describe the development of the first spaceflight prototype of a fully automated subcritical water extractor designed to provide this essential functionality on a potential future planetary mission. The prototype extractor was mounted on a Mars test rover platform and successfully operated remotely in the Atacama Desert, Chile. Samples acquired by the rover's drill and sample acquisition/delivery system were remotely transferred to the extractor inlet funnel, and all subsequent extractor operations were performed automatically. To validate the instrument and demonstrate its suitability as a front-end unit for an organic analyzer, we tested low-bioload Atacama Desert soil extracts for amino acid content using capillary electrophoresis coupled to laser-induced fluorescence. We show that hot extraction under subcritical conditions is required to liberate amino acids from the sample, as no amino acids were found in the extract produced at room temperature. Plain Language SummaryThe search for signs of life beyond Earth is one of NASA's highest priorities. One powerful way to look for extraterrestrial life is to perform chemical analyses on planetary samples in order to characterize any organic molecules present. Past and current spaceflight instruments analyze various components in gases collected or gases produced from solid samples; however, the instruments either lack the sensitivity to detect organic molecules or the instruments destroy many of the organic molecules during the preparation required to perform a gas-phase-based measurement. This work presents an automated pressurized hot water extractor that can be used to release organic molecules from a solid sample. Pressurized hot water is a powerful and easy-to-handle solvent for a wide range of different compounds. The extractor acts as a front-end instrument and prepares the sample for highly sensitive, liquid-based analysis. This automated and remotely controlled prototype has been successfully tested on a simulated Mars rover mission in the Atacama Desert in Chile. Extracts of the Atacama soil samples were then analyzed by capillary electrophoresis coupled to laser-induced fluorescence to determine the extracts' amino acid content, as amino acids are an auspicious class of molecules in the search fo...

Science Objectives for Flagship-Class Mission Concepts for the Search for Evidence of Life at Enceladus

“…The SPS would either deliver pristine liquid directly to an instrument or conduct preparation steps depending on the needs of the instrument ( e.g ., Chinn et al , 2017 ; Chin et al , 2018 ; Kehl et al , 2019 ; Radosevich et al , 2019 ). Derivatization reactions, for example, are key for the amino acid and lipid hydrocarbon analyses conducted with instruments such as the microcapillary electrophoresis with laser-induced fluorescence (μCE-LIF) and the SMS.…”

Europan Molecular Indicators of Life Investigation (EMILI) for a Future Europa Lander Mission

“…OCEANS operation begins at the LEM, which allows hightemperature extraction (200 °C) to release adsorbed organics and lyse any cells. These extraction methods have been described in detail previously (Amashukeli et al, 2007;Noell et al, 2018;Kehl et al, 2019), and more details on the design and performance of the LEM are provided below. Extracted sample is then drawn into the SPU using an internal piston pump.…”

Extraction and Separation of Chiral Amino Acids for Life Detection on Ocean Worlds Without Using Organic Solvents or Derivatization

“…It is important to note that no extraction optimization was performed for the superheated water extraction of amino acids from solid samples due to limited sample amounts. However, several studies have been performed showing the importance of heat to desorb amino acids from solid samples (Amashukeli et al, 2007(Amashukeli et al, , 2008Kehl et al, 2019). It has also been demonstrated that performing superheated water extraction with an acidic solvent using hydrochloric acid improves analyte recovery (Noell et al, 2018).…”

“…with demonstrations with analog sample matrices, field studies, and prototype hardware (Aubrey et al, 2008;Bada et al, 2008;Kehl et al, 2019). Although more studies are needed to determine extraction conditions and the influence of various matrices on recovery of relevant analytes, the technique is steadily becoming more mature.…”