JIMO spacecraft (Jupiter Icy Moons Orbiter) near Jupiter, composite computer artwork. This unmanned spacecraft is designed to study the three icy Galilean moons of Jupiter: Callisto, Europa and Ganymede. These moons may harbour vast oceans of water beneath their surfaces, and the JIMO probe will determine whether or not they can support life. JIMO is being designed as part of Project Prometheus (formerly the Nuclear Systems Initiative), which aims to develop new nuclear-based propulsion and power systems for spacecraft. These will allow for faster, more efficient and longer-lasting exploration missions.