The Enceladus Orbilander Mission Concept: Balancing Return and Resources in the Search for Life

Abstract

Enceladus’s long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon’s surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.

Contamination Control for Ultra-Sensitive Life-Detection Missions

“…These L1 science requirements include instrument requirements with some margin (i.e., instrument performance specifications) and mission requirements and were based on the expected abundances of amino acids and lipid hydrocarbons in the Enceladus Ocean, sampled by an orbiter from a cryovolcanic plume. These values are published elsewhere (MacKenzie et al, 2021), and assume a total organic content (TOC) 2 in the Enceladus Ocean of 30 μM (similar to the value assumed for Europa in Hand et al, 2017). For simplicity, expected amino acid and lipid abundances were defined in moles and referenced to instrument LoD and SNR, assuming a minimal sample volume of 2 μL obtained after one flythrough of the Enceladus plume (Table 1 in Porco et al, 2017).…”

“…Robotic missions that aim to detect, identify, and measure possible biomolecules, determine signatures-of-life parameters, and ultimately determine whether life exists or has existed in an extraterrestrial planetary environment (McKay et al, 2013;Reh et al, 2016;Hand et al, 2017;Eigenbrode et al, 2018;Turtle et al, 2018;Williford et al, 2018;MacKenzie et al, 2021) must implement steps that mitigate the risks of false positive detections. Possible sources of false positives in missions evaluating signatures of life (herein referred to as "lifedetection missions") include contaminants such as terrestrial cells, cellular parts, biomolecules, and anthropogenic interferences.…”

“…First, is the realization that signatures of life such as biomolecules in other planetary bodies of the Solar System are likely to be present at very low abundances, and therefore might be easily obscured by small amounts of terrestrial contaminants. Second, prompted by the expected low abundances of biogenic compounds, existing flight instruments capable of detecting biomolecular signatures have achieved exquisite levels of detection (LoD) and can measure target compounds at pico-to femtomole levels (Hand et al, 2017;MacKenzie et al, 2021) the mole equivalent to the molecular content in 1-10 bacterial cells. However, the trade-off of ultrasensitivity is the risk of detecting contaminants, potentially preventing, obscuring, or confounding the detection of native molecules (false negative) or causing false positive detections.…”

Planetary Mass Spectrometry for Agnostic Life Detection in the Solar System

“…Other mission concepts to Europa have also begun to integrate agnostic search strategies to account for the presence of potentially unfamiliar life forms (Mahaffy et al, 2021). In addition, sample return missions have been proposed for Mars and Enceladus to leverage the use of multiple instrument platforms to look for signs of life once the samples are back on Earth (Muirhead et al, 2020;Neveu et al, 2020;MacKenzie et al, 2021), especially those that have yet to be miniaturized for flight (e.g., nano-SIMS). Because agnostic life detection strategies can be implemented in near future missions, emerging concepts in agnostic biosignatures are concurrently being optimized in the laboratory in order to enhance the science return and increase our confidence in any future potential life detection measurements.…”

MEMS GC Column Performance for Analyzing Organics and Biological Molecules for Future Landed Planetary Missions

“…Abiotic processes produce smooth distributions of organic material whereas biotic, or biological, processes use the "Lego Principle" (McKay, 2004), introducing selectivity into their organic building blocks (Summons et al, 2007). Icy worlds astrobiology mission concepts include both the Flagship Europa Lander (Hand et al, 2017) and Enceladus Orbilander concepts (MacKenzie et al, 2021a;2021b) which would land on the surface of these planetary bodies and sample the ice and potentially plume fall out. An Enceladus life detection mission in particular has strong scientific justification based on recent findings from the Cassini mission (Cable et al, 2021).…”