This ‘family portrait’ shows a composite of images of Jupiter, including it’s Great Red Spot, and its four largest moons. From top to bottom, the moons are Io, Europa, Ganymede and Callisto. Europa is almost the same size as Earth’s moon, while Ganymede, the largest moon in the Solar System, is larger than the planet Mercury.
While Io is a volcanically active world, Europa, Ganymede and Callisto are icy, and may have oceans of liquid water under their crusts. Europa in particular may even harbour a habitable environment.
Surface temperature: -223°C to -108°C
Atmosphere composition: Io has a thin sulfur dioxide atmosphere, Callisto has a very thin carbon dioxide atmosphere, both Europa and Ganymede have tenuous oxygen atmospheres.
Radiation: High
Magnetic field?: Ganymede is the only moon in the Solar System with a magnetic field
Acceleration of gravity: 1.2 to 1.8 ms-2