A possibility is that carbon-dioxide ice at the moon's surface slowly sublimates away into the atmosphere. Because it is so rarefied, the atmosphere would escape to space in a few days as such, there has to be a process at Callisto that continually replenishes carbon dioxide. A key goal for JUICE is to find out the role the ionosphere plays in producing the measured field, to separate this contribution from that of the interior liquid layer and to better constrain the ocean's properties.įinally, JUICE will investigate Callisto's thin atmosphere, which is mostly composed of carbon dioxide.

Galileo's measurements of an induced magnetic field at Callisto could also be explained, in part, by an ionosphere capable of conducting electric current. In addition, JUICE's ice-penetrating radar will map the moon's subsurface down to a few kilometres to investigate the icy shell. If a subsurface ocean does exist, JUICE will study its properties, and constrain the thickness of the icy crust above it. That mission detected an induced magnetic field at Callisto with characteristics that suggest the moon could have an underground layer of liquid salty water.īy investigating the moon's gravity field and shape, JUICE's instruments will be able to probe Callisto's interior structure, including its degree of differentiation. In addition, the Galileo spacecraft found evidence for a possible subsurface ocean. Callisto is thought to have some differentiated layers in its interior: a small rocky inner core surrounded by a mantle mostly made up of ice.

The mission will also study the moon's subsurface and interior. Researchers aim to identify the various organic and non-organic compounds that make up the moon's surface, relate them to the moon's geology, and understand how high-energy particles from the Jovian space environment can alter Callisto's surface composition, a process called space weathering. Scientists hope to find out how much of a role tectonics and other geologic processes played in moulding the moon's surface in the past, and how much influence impact activity has had in Callisto's evolution.Īt the surface, JUICE will study the composition and chemistry of Callisto's rocky and icy materials. The mission's observations will allow us to constrain the moon's surface ages, both at the global and local scales, and to study erosion and asteroid-dust deposition processes on Callisto's landforms. JUICE will investigate Callisto's cratered surface in detail to find out more about the moon's past activity. As such, it can provide scientists with a unique window to explore the early stages of formation of the Galilean moons. The lack of resurfacing or other signs of geologic activity on the moon's surface point to Callisto being a long-dead world, a remnant of the early Jovian system. In fact, Callisto's surface is the oldest and most densely cratered of any body in the Solar System. A fossil from the formation eraĬallisto has an old, heavily marked landscape, with impact features covering the moon's entire surface and with landforms showing signs of intense erosion. The 1 880 000 kilometre distance from Jupiter, and the fact that Callisto is relatively isolated from the other Galilean satellites, also means that tidal heating at the moon is not significant, making it far more geologically stable than the inner Galilean moons. Because of its remote location, orbiting beyond Jupiter's main radiation belts, Callisto sees lower radiation levels and less influence from the Jovian magnetosphere than Ganymede and Europa. Like both Ganymede and Europa, Callisto is thought to have a large ocean beneath its surface, although the evidence for this is less compelling than for the other two moons.ĭespite these similarities, in many ways this Galilean moon is very different from its icy companions. Like Ganymede, the moon is similar in size to Mercury but, with less than a third of that planet's mass, it is the least dense of all the Galilean moons. To better contrast and compare Jupiter's icy worlds, in addition to investigating Ganymede and Europa, JUICE will also study Callisto, the outermost and second-largest Galilean satellite.

Does callisto experience tidal heating