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upstart writes:

Europe's JUICE probe will investigate three of Jupiter's largest ice moons for signs of potential habitability:

JUICE, short for JUpiter ICy moons Explorer, is headed for Jupiter, but the spacecraft will focus its observations on three of the gas giant's many moons: Europa, Ganymede, and Callisto. Jupiter, the largest planet in the solar system, hosts more than 70 natural satellites, but these three Galilean moons are thought to hold immense amounts of subsurface water hidden beneath thick layers of ice (Io is the fourth Galilean moon, but it's an inhospitable volcanic hellhole). JUICE, an international collaboration headed by the European Space Agency, will spend three to four years at Jupiter, performing flybys and making detailed observations of the three icy moons and their immediate surroundings.

[...] JUICE will reach Jupiter in 2031 following an eight-year journey, but to get there it'll need to receive four gravity boosts from Earth and Venus. Excitingly, the spacecraft's flyby of the Earth-Moon system, a maneuver known as a Lunar-Earth gravity assist (LEGA), has never been attempted before. As ESA explains, JUICE will first get a gravitational assist from the Moon and then a second from Earth some 1.5 days later, in a maneuver meant to "save a significant amount of propellant."

Europa, Ganymede, and Callisto are all suspected of containing subsurface oceans capped in an icy crust. JUICE will evaluate the trio for potential signs of habitability, given the assumed presence of liquid water. Indeed, and as ESA makes clear, the overarching question of the mission is whether gas giants can harbor habitable conditions and spawn primitive life. In addition to its astrobiological duties, JUICE will seek to answer questions about planetary formation and the solar system in general. More conceptually, the spacecraft will evaluate the "wider Jupiter system as an archetype for gas giants across the Universe," according to ESA.