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

Abstract

Cassini revealed that Saturn's Moon Enceladus hosts a subsurface ocean that meets the accepted criteria for habitability with bio-essential elements and compounds, liquid water, and energy sources available in the environment. Whether these conditions are sufficiently abundant and collocated to support life remains unknown and cannot be determined from Cassini data. However, thanks to the plume of oceanic material emanating from Enceladus’ south pole, a new mission to Enceladus could search for evidence of life without having to descend through kilometers of ice. In this article, we outline the science motivations for such a successor to Cassini , choosing the primary science goal to be determining whether Enceladus is inhabited and assuming a resource level equivalent to NASA's Flagship-class missions. We selected a set of potential biosignature measurements that are complementary and orthogonal to build a robust case for any life detection result. This result would be further informed by quantifications of the habitability of the environment through geochemical and geophysical investigations into the ocean and ice shell crust. This study demonstrates that Enceladus’ plume offers an unparalleled opportunity for in situ exploration of an Ocean World and that the planetary science and astrobiology community is well equipped to take full advantage of it in the coming decades.

In situ organic biosignature detection techniques for space applications

“…However, their simplicity and ability to interrogate Frontiers in Astronomy and Space Sciences frontiersin.org a vast number of samples will render them invaluable for sample selection for further analysis by instruments that are limited by the number of samples that can be analyzed. On the basis of the reviewed literature, the next-generation biosignature detection techniques for planetary applications (CE, LC, biosensors, and nanopore sensing) are mostly fit for science requirements in mission concepts that include life detection (Pappalardo et al, 2013;Hand et al, 2017;MacKenzie et al, 2022a;MacKenzie et al, 2022b;Williams and Muirhead, 2022). Current GC-MS, fluorescence, and Raman spectroscopy instruments cannot achieve the required LODs.…”

“…Specifications are mission-dependent. However, lower limits of detection (LOD) of 1 ppb (Mahaffy et al, 2012;Pappalardo et al, 2013) or even lower (Hand et al, 2017;MacKenzie et al, 2022b) are often required.…”

Divergent behavior of hydrothermal plumes in fresh versus salty icy ocean worlds

“…Čadek et al, 2019;Kvorka et al, 2018) using model results from solid core processes. Finally, an efficient transport from seafloor to ice shell (and potentially to the surface through jets or other cryovolcanism) is a key motivator for future space missions to these bodies seeking extraterrestrial life, especially mission concepts arguing for landing on the ice shell and scooping surface material deposited by the plumes (Choblet et al, 2021;MacKenzie et al, 2022). Typically, it has been assumed that, in analogy with deep sea hydrothermal vents on Earth, the seafloor on icy ocean worlds is likely the most habitable environment on such bodies.…”

Testing of Ion Exchange Solid Phase Extraction Media for Extraterrestrial In Situ Sample Preparation on Liquid Samples

“…In addition to hydrogen and sodium salts, , complex organic molecules were detected in these plumes , including those containing nitrogen and oxygen . The push to further explore Enceladus is highlighted in recent publications detailing a flight concept mission to Enceladus, incorporating both an orbiter and a lander component. , Collection of ejected ice particles by an orbiter would protect the moon from contamination by terrestrial material, but the amount of material that could be collected for analysis would be limited. A lander provides the potential to collect and analyze larger samples collected directly from the subsurface ocean or icy material near the plumes that contain direct ejecta material.…”