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...