INVESTIGATING THE INTERIOR OF ICY WORLDS WITH SMALL APERTURE SEISMIC ARRAYS

The interiors of the icy outer satellites are currently of great interest as they may support the largest volume of habitable space within the Solar System. A key parameter of this habitability is the presence of liquid water oceans or seas beneath the frozen surface, thus geophysical investigations of the interior are crucial for understanding the structure, dynamics, and evolution of these liquid water reservoirs. Seismology is a powerful tool for illuminating the deep interior, and will be an invaluable method for determining the thickness of ice shells, the depth of underlying oceans, underlying silicate bodies, and assessing Icy Worlds for habitability. Our present understanding of the seismic signals produced by Icy Worlds is limited, with the level of seismic activity at the surfaces (and interiors) likely driven by tidal processes. The harsh operating environments will limit mission observation times, making it is essential that the seismic information returned from a surface mission be of high fidelity in resolving key questions about the internal environment of an Icy World.

Here we present new modeling results that demonstrate the improved knowledge provided by a small aperture seismic array. We define a small aperture array as a deployment of multiple 3-component seismometers, with a separation between instruments of 1-10 meters. The instruments in the array must have a sampling rate and frequency range sensitivity capable of distinguishing between waves arriving at each station. We will present 3-D synthetic modeling results that demonstrate sensing requirements and the primary advantages of such a seismic array over a single station, including the improved ability to resolve the location of the source through detection of backazimuth and differential timing between stations, ambient noise techniques, as well as the ability to improve the signal to noise ratio by additive methods such as stacking and velocity-slowness analysis. We also compute a series of modeled noise functions for Europa and Enceladus based upon periodic tidally induced stress on surface faults to estimate the types of signals and noise that would be observed by a seismic station. These results will inform future missions and planning of landers on the surfaces of Europa, Enceladus, Titan, and other objects in the outer Solar System.