2022

Jupiter Icy Moons Explorer

As the largest moon in the solar system, Ganymede has been the focus of a significant amount of study by the Voyager and Galileo missions. Those encounters revealed that Ganymede is a world that has been segregated into a rocky/metallic core, icy/rocky mantle, and an icy crust, similar in some ways to its neighboring moon Europa. Ganymede has a more heavily cratered surface than Europa, however, suggesting less recent resurfacing and perhaps less internal activity. Surprisingly, however, Ganymede has its own magnetic field, and previous studies have used the nature of that field to infer the presence of a liquid water layer—a subsurface ocean—beneath that moon’s icy crust.

The European Space Agency plans to launch a mission called Jupiter Icy Moons Explorer, or JUICE, in 2022 to attempt to confirm the existence of Ganymede’s subsurface ocean, as well as to study its neighboring icy moons Europa and Callisto in greater detail than previous missions. JUICE is a solar-powered spacecraft that will arrive into Jupiter orbit in 2030 and conduct flybys of all the major moons before transitioning into orbit around Ganymede itself in 2033. Science instruments include ultraviolet and visible wavelength cameras and spectrometers, ice-penetrating radar and magnetometer investigations to search for and characterize the ice/ocean boundary, and a variety of other instruments to study the magnetic fields and plasma environments of Jupiter and Ganymede. Because NASA’s Europa Clipper mission should also have arrived in the Jupiter system several years earlier, significant synergy and coordinated observations between that mission and JUICE are envisioned.

If Ganymede is found to harbor a large subsurface liquid water ocean, then it would join Europa as an extremely compelling astrobiology “hotspot” in the solar system, where liquid water, heat sources, and organic molecules combine to yield a potentially habitable environment. Whether or not these distant worlds are actually inhabited, however, will likely have to await future missions that are able to land on and drill deeply into their icy crusts, and perhaps even explore and sample their subsurface oceans directly.

Artist’s rendering of the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission, which will study the interior of Ganymede (shown here in a hypothetical cutaway view); Jupiter’s other large moons Europa, Io, and Callisto; as well as other aspects of Jupiter’s environment, such as magnetic fields and high-energy charged particles.