Subsurface Science and Search for Life in Ocean Worlds

Abstract

Several worlds in our solar system are thought to hold oceans of liquid water beneath their frozen surfaces. These subsurface ice and ocean environments are promising targets in the search for life beyond Earth, but they also present significant new technical challenges to planetary exploration. With a focus on Jupiter’s moon Europa, here we (1) identify major benefits and challenges to subsurface ocean world science, (2) provide a multidisciplinary survey of relevant sample handling and life detection technologies, and (3) integrate those perspectives into the Subsurface Science and Search for Life in Ocean Worlds (SSSLOW) concept payload. We discuss scientific goals across three complementary categories: (1) search for life, (2) assess habitability, and (3) investigate geological processes. Major mission challenges considered include submerged operation in high-pressure environments, the need to sample fluids with a range of possible chemical conditions, and detection of biosignatures at low concentrations. The SSSLOW addresses these issues by tightly integrated instrumentation and sample handling systems to enable sequential, complementary measurements while prioritizing preservation of sample context. In this work, we leverage techniques and technologies across several fields to demonstrate a path toward future subsurface exploration and life detection in ice and ocean worlds.

Development of the Miniature Robotic Electrodialysis (MR ED) System for Small-Scale Desalting of Liquid Samples with Recovery of Organics

“…Two liters of sample were gathered and filtered to remove particles larger than 0.7 µm before they were tested with MR ED to prevent clogging the tubing, interior channels, and mem- branes. In planetary missions, pre-filtration would be a likely step prior to other processing (Lawrence et al, 2021), as is standard in ocean sampling. We processed these samples with Concentrate 1 and achieved an average of 72% DOC recovery.…”

“…The Miniature Robotic Electrodialysis system was designed for desalting small volumes of sample (less than 100 mL) as technology development for a liquid sample handling system for future ocean world missions for which proposed instruments would require desalting prior to analysis (Lawrence et al, 2021). However, such a small system has applications both on Mars and for field use Earth, allowing desalting of samples for many uses.…”

“…Increasingly, sampling and sample handling systems for planetary missions that seek to detect evidence of life include multiple "phases" of measurements by suites of instrumentation with increasing sample processing complexity; some instruments require little to no processing, whereas others require extensive processing (Hand et al, 2021(Hand et al, , 2017Mahaffy et al, 2012). This latter category of instruments includes mass spectrometry and nanopore sequencing, both of which require direct contact and interaction with a sample within the spacecraft (Hand et al, 2021(Hand et al, , 2017Lawrence et al, 2021). In order to measure organics and search for other biomarkers, future missions will require the ability to both concentrate material and remove confounding salts that can alter such chemical measurements, in particular mass spectrometry that is a cornerstone of landed missions (Franz et al, 2014;Grubisic et al, 2021;Hand et al, 2017).…”

“…Moreover, as in situ sequencing of samples becomes possible onboard spacecraft, extraction efficiency of DNA by nanopore sequencers is greatly reduced in solutions with high salt concentration (Weng et al, 2019). Thus it has been recommended that methods to remove salts in milliliter to microliter-scale samples while preserving organic compounds within the sample be developed, in order to create water samples suitable for analytical life detection techniques that are confounded by high salinities (Lawrence et al, 2021).…”

Development of the Miniature Robotic Electrodialysis (MR ED) System for Small‐Scale Desalting of Liquid Samples With Recovery of Organics

“…These successful electrodialysis systems are large and have been used to process between 0.5 and 200 L of sample; however, miniaturized systems require further development to achieve similar recovery, and require design changes to function as a part of a science package on spacecraft that explore liquid environments, such as those on ocean worlds. Minimization of sample volumes to the 10–100 mL scale (Lawrence et al., 2021) has many advantages including reduction of instrument size and power requirements if the science value can be preserved. Additionally, miniaturization is advantageous for making the process field portable for investigations in remote locations on Earth by reducing the logistics of collecting large volumes of sample.…”