Moons of Jupiter
Jupiter’s natural satellites range from small, irregular captured bodies to the four large Galilean moons: Io, Europa, Ganymede, and Callisto.
Io: Io is Jupiter’s innermost Galilean moon and the most volcanically active world in the Solar System. Its intense volcanism makes it the system’s clearest example of tidal heating.
Laplace resonance: The Laplace resonance links the orbital periods of Io, Europa, and Ganymede in a 1:2:4 ratio. Their resonance maintains orbital eccentricities that help power tidal heating.
Circumjovian disk: A circumjovian disk is a disk of gas and solids orbiting Jupiter during its formation. The Galilean moons are thought to have accreted from material in this disk.
Galileo spacecraft: Galileo was a NASA spacecraft that studied Jupiter and its moons from orbit between 1995 and 2003. Its measurements transformed knowledge of the Galilean moons and detected evidence for Europa’s ocean.
Moons of Saturn: Saturn’s natural satellites include Titan, an atmosphere-rich moon, and Enceladus, an active icy ocean world. Saturn’s moon system offers a different mix of prominent ocean worlds and atmospheric environments.
Europa: Europa is an icy Galilean moon with a global subsurface ocean beneath its fractured surface. Its hidden ocean makes it a leading target in the search for extraterrestrial life.
Tidal heating: Tidal heating is internal warming caused by repeated deformation under changing gravitational forces. It drives Io’s volcanism and may help sustain liquid water beneath icy moons.
Capture (astronomy): Gravitational capture is the process by which an orbiting body becomes bound to another body after losing orbital energy. Capture offers an origin for many distant, irregular Jovian satellites.
Juno (spacecraft): Juno is a NASA spacecraft studying Jupiter’s gravity, magnetic field, atmosphere, and interior. Its close passes have also produced observations of Jupiter’s moons, including Ganymede and Europa.
Moons of Uranus: Uranus’s natural satellites include five major moons and many smaller bodies orbiting the ice giant. Their system lacks a Galilean quartet comparable in scale and dynamical influence.