Deep Ocean Passive Acoustic Technologies for Exploration of Ocean and Surface Sea Worlds in the Outer Solar System

Ocean worlds are numerous in our solar system. Here, we present an overview of how passive acoustic monitoring (PAM) and signal detection systems, developed for acoustic sensing in Earth's ocean, might be used to explore an ocean and/or surface sea world in the outer solar system. Three potential seagoing mobile platforms for a PAM system are considered: a saildrone or surface buoy for exploring Saturn's largest moon, Titan, and an autonomous underwater vehicle for exploring the sub-ice oceans of Enceladus, one of Saturn's smaller moons, or Europa, one of Jupiter's larger moons. We also evaluate preparation of an acoustic system and electronics for the rigors of spaceflight and the challenging environments of outer solar system planetary bodies. The relatively benign Europa/Enceladus ocean thermal environment (-40 degrees to 40 degrees C) suggests a standard commercial acoustic product may meet system design needs. In comparison, a PAM system for Titan's hydrocarbon seas must function at -180 degrees C temperatures, necessitating testing in liquid nitrogen. We also discuss adapting for outer ocean world exploration, acoustic signal detection, and classification algorithms used widely in ocean research on Earth, as well as data compression methods for interplanetary transmission. The characteristics of geophysical, cryogenic, and meteorological acoustic signals expected in an ocean or surface sea world, including signals from seafloor cold seeps and/or hydrothermal vents, are considered because of their potential to harbor chemosynthetic life.