Icy Worlds like Europa and Enceladus provide conditions for the survival of microorganisms. Conducting life detection in regions with high biological potential, such as the icy shell, ice-water interface and seafloor, is likely to discover robust biosignatures, extant life and even prebiotic chemical systems. Extraterrestrial Autonomous Underwater Vehicles (Exo-AUVs) are able to perform in situ, multi-object, multi-scale and multi-dimensional detection autonomously and efficiently. They are expected to serve as crucial tools for planetary scientists and astrobiologists exploring icy worlds and searching for extraterrestrial life.
Based on Europa, it is suggested that the primary science goal of Icy Worlds life detection missions should be the exploration of biological potential which not only aligns with the hypothetical nature of a detection but also helps avoid potential paradoxes associated with binary thinking. By focusing on biological potential, researchers are likely to uncover biosignatures, extant life and even prebiotic chemical systems. The speculation, evaluation and verification of biological potential require consideration of numerous environmental variables and parameters, some of which may serve as biosignatures indicating the presence of life. Just as on Earth, where life thrives in some regions but is scarce in others, detecting the biological potential of Europa should prioritize regions with relatively greater potential for supporting life and biosignatures. Drawing on analogies and ecological theories on Earth, researchers can identify key regions with high biological and biosignature potential, such as the icy shell, ice-water interface and seafloor. However, current detection methodologies often focus on biogenic analysis and overlook strategies for collecting robust biosignatures. In oligotrophic systems, life distribution is sparse and heterogeneous. Even in theoretically promising regions like beneath the ice or on the seafloor, fragile biosignatures may be unable to define biogenesis, regardless by the binary diagnosis or statistical methods.
The process of detecting life on Icy Worlds involves four key procedures: assuming, sampling, analyzing and verifying. The Exo-AUV, along with its ice-penetrating carrier, has the capability to explore the subsurface of the icy shell and carry various payloads for comprehensive data collection and analysis in different dimensions. By applying the ecological niche theory, a life detection strategy for Icy Worlds has been proposed. This strategy guides the Exo-AUV to autonomously identify micro-zones with high biological potential, collect diverse robust biosignatures and potentially detect extant life. The data gathered from Icy Worlds can be used to validate, refute, refine and even reconstruct models based on Earth data. By leveraging the Exo-AUV's underwater detection capabilities, this strategy overcomes limitations of passive data collection and integrates assuming, sampling, analyzing and verifying procedures into a comprehensive methodology for detecting life on Icy Worlds. Ultimately, this strategy aims to uncover robust biosignatures, potential extant life and even prebiotic chemical systems in Europa's thick icy and oceanic layers of hundreds of kilometers thick, with minimal energy and supplies.
Three typical contexts for detecting life on Europa are identified, within the icy shell, at the ice-water interface and on the seafloor. Each context is composed by 4 major contextual elements, environmental conditions, Exo-AUV, the object being measured and key operations. By analyzing these contextual elements along with other pre-procedures such as launching, interplanetary flight, orbit entry and landing, the basic technological requirements for the Exo-AUVs and their ice-penetrating carrier are proposed.
Europa's icy shell and under-ice ocean are both globally distributed. The icy shell thickness may reach about tens of kilometers, with hydrostatic pressure at the deepest ocean floor points potentially doubling that of the Mariana Trench on Earth. Ice-penetrating carriers can utilize Small Modular Reactor (SMR) or Radioisotope Thermal Generator (RTG) power and heat sources, employing a thermal-mechanical hybrid penetrating method and energy-efficient hull design. Navigation assistance can be provided through the use of sonar or synthetic aperture radar, with lateral nozzle jets or auxiliary heat aiding in steering and obstacle avoidance. The carrier penetrates the icy shell to deploy Exo-AUVs into the water, serving as under-ice base station for navigation, communication, data exchange and charging services. The Exo-AUVs are constructed with pressure-resistant hull materials, equipped with RTG power supplies, high-performance navigation and communication modules. They are able to cruise and glide across large space with variable buoyancy, hover around local micro-zones and lean against the undersurface of the icy shell or on the seabed, covering a range from small to large scales.
In order to discover sparse and heterogeneously distributed robust biosignatures and extant life in the vast ice and sea expanse, the Exo-AUV and its ice-penetrating carrier must take a variety of science payloads aboard. These payloads will encompass acoustics, vision, spectroscopy, electrochemistry, analytical chemistry, cell biology and molecular biology instruments. The exploration will gradually focus on objects with different characteristic lengths ranging from several kilometers to sub-micrometers. The collected in situ multi-dimensional information includes morphology, structure, composition, movement, distribution, physiochemistry and etc., and will enables online ecological niche and biogenic analysis. Europa, being far away from Earth, poses challenges due to limited payload capacity of the launch vehicle. The strong radiation from Jupiter above the icy surface demands for protective materials. To address these challenges while ensuring detection capability, microelectromechanical systems (MEMS) technology is employed to achieve payload miniaturing and lightweighting.
The communication delay between Europa and Earth can be as long as 0.5 hours, with a narrow bandwidth and limited window for data exchange. This restricts frequent manual intervention and high-throughput data transfer. In missions focused on detecting complex life, the probe's autonomy becomes crucial. Firstly, Exo-AUV and its ice-penetrating carrier should autonomously localize, navigate and plan the path based on acoustic and optical sensors, and control the propeller, steering rudder and buoyancy to adjust the speed, depth and pose. In addition, based on the detection strategy proposed in this study, Exo-AUV should also achieve science autonomy, speculate potential regions in different scales of space, plan detection tasks, utilize a variety of payloads to complete data acquisition and analysis directly or through onboard tests, verify the assumptions of biological and biosignature potential, update the computational model, summarize, sort and transmit important data independently.
Exo-AUVs developed in the United States and Europe are examined, revealing that current designs lack the capability to tackle intricate life detection tasks and are yet to fully exploit the full potential of the Exo-AUV platform. To prevent stepping into the same old tracks of the Viking missions, a roadmap for conceptual development of Exo-AUVs tailored for detecting life on Icy Worlds is outlined. This roadmap encompasses crucial factors that shape the Exo-AUV concepts. Based on science goals, it is a guideline for the Exo-AUV developers on exploring potential regions, objects detectable and detection strategies, analyzing key contextual elements, refining technological requirements, designing and evaluating concepts with different hull design, payloads and autonomy.
A Concept of Operations for Multiple Exo-AUV System (ConOps for MEAS) is proposed. A simplest MEAS is consisting of an ice-penetrating Exo-AUV Carrier (EAC), a Survey Module-equipped Exo-AUV (EAS) and an Observation Module-equipped Exo-AUV (EAO). The EAC utilizes either an RTG or SMR for power or heat sources and employs a thermal-mechanical hybrid penetrating technique for ice penetration. The EAS and EAO can be housed within the EAC, with all three capable of communication and data sharing through acoustics or fiber optic interfaces. The EAS, featuring a foldable wing-body hull and RTG power supply, is designed for prolonged cruising and gliding within full sea depth, detecting large objects at the ice-water interface and on seafloor. Conversely, the EAO, with a disc-like hull design, full thrusters, rechargeable batteries and various MEMS task payloads, excels at detecting small objects in localized micro-zones. The EAS can connect and disconnect with the EAO in water, acting as a vehicle for transporting, charging and data exchanging. Notably, the MEAS is tailored to address the diverse contextual elements of different potential regions of Europa, where detectable objects and measuring scales vary significantly in size. By distributing technological requirements among the Exo-AUVs, the MEAS efficiently tackles challenges such as idle loads, wasted space, weight, energy and the launch vehicle loading capacity limitations. This concept also enhances maneuverability, robustness, survivability and operational efficiency. In the event of major discoveries, additional MEASs can be launched to create a detection network covering the vast global ice and sea expanse.
See the article:
An Icy Worlds life detection strategy based on Exo-AUV, https://doi.org/10.1007/s11430-023-1390-6
