Seismometers for Exploring the Subsurface of Europa (SESE)

Studies of landed mission concepts to Jupiter's ocean moon, Europa, have identified a seismometer, or geophone, as a key instrument to characterize Europa's tectonic activity, identify near-surface liquid water, and constrain the interior structure including the depth of the ice-ocean interface. The potential of a seismometer to identify liquid water that would be accessible to a lander will, in fact, be critical to achieving the goal of NASA's Ocean Worlds and Outer Planets program: to enable identification of extant life on another world. However, uncertainties about the surface of Europa present particular challenges to a seismic instrument deployment, which may affect the penetration depth and installation angle and stability of a seismic sensor. Furthermore, unknown trade-offs exist between pursuing seismological goals with a single seismometer versus a localized array of seismic sensors. Finally, Europa's radiation and extremely low-temperature environment is substantially different from the Moon, or Mars, where seismic experiments have been planned and/or carried out. The goal of this proposal is to mature a miniature broadband seismometer for deployment on Europa to probe the properties of its ice shell and interior structure and record current activity. Recent advances in MicroElectroMechanical System (MEMS) have enabled optimization of seismometers for spaceflight seismic instrumentation. For example, a seismometer package is the primary instrument of the InSight mission and consists of a 3-axis very-broadband instrument, which is a traditional pendulum system, and a 3-axis short period MEMS seismometer, built with silicon-based microfabrication. However, this package has not yet achieved the simultaneous requirements for low mass and power, high robustness, and high performance. Its theoretical noise floor is limited in short period, and the vacuum packaging issue has postponed launch for at least for two years. Furthermore, its tolerance on shock (2kG) and installation angle (±15°) limits its potential use in other missions, especially with unknown icy surface conditions on Europa. We propose to mature a broadband miniature seismometer, which uses a MEMS sensing element with ionic liquid based electrolyte as the sensing body. This design will serve as the basis of a flight instrument for a Europa lander mission, currently under study. This new instrument provides both high sensitivity and dynamic range, broad-band response, and high environment tolerances, reaching or exceeding the requirements for Europa lander mission suggested from JPL Europa lander report. It also has the advantage of flexible deployment methods due to its high shock tolerance (>25 kG), ±180° tilt tolerance, and no requirement of vacuum sealing. We will achieve this goal through three objectives: 1) Maturation of miniature seismometer technology for use in Europa's environment, 2) Determine optimal sensor deployment configuration through field testing with existing seismometers, 3) Model the expected seismicity of Europa and the corresponding instrument capabilities and requirements to achieve lander mission objectives. Our proposed work is relevant to the COLDTech program, as it would bring seismic sensor cell, the core mechanical hardware of a seismometer instrument, to Technology Readiness Level 6 (TRL 6) for the potential Europa lander mission. The proposed activities would “develop and advance the maturity of science instruments, especially those focused on the detection of evidence of life, especially extant life, in the ocean worlds of the outer Solar System” and provide “spacecraft technologies required to access the oceans.”. The seismometer we are developing will be capable of identifying and physically characterizing the most likely habitats on Europa. Its unique robustness and flexibility will mitigate risk for the Europa lander mission and provide a new tool for future exploration of other ocean worlds. More »