Science goals for future exploration of the habitability of the gaseous giant planets' satellites

摘要

Large satellites of gas giants, at orbits beyond the snow-line and the traditional "habitability zone", such as around Jupiter or Satum, can contain a large amount of water (almost 45% in mass). Their hydrospheres are extremely thick (~600 km for Ganymede and Callisto for instance), and may possess liquid layers below the icy crust. Around Saturn, Enceladus and Titan have also been recognized as potentially having undersurface liquid water reservoirs. Thus, the icy satellites provide a conceptual basis within which new theories for understanding habitability can be constructed. Measurements from the Voyager and Galileo spacecraft revealed the potential of these satellites in this context. Future exploration towards the Galilean satellites include missions such as ESA's JUpiter Icy moons Explorer (JUICE) or NASA's Europa Clipper. For a return to Titan, NASA has recently selected the Dragonfly mission and other concepts are being studied. Such endeavors will greatly enhance our understanding of the icy moons, their potential habitability and the formation of the Solar System in general.