You are here: Space > Planets and moons > Galilean moons

Galilean moons

The four Galilean moons and part of their parent planet Jupiter, to scale Jupiter’s four largest moons (it has 67 in all) are called the “Galileans” after the Italian scientist Galileo Galilei (1564–1642) who discovered them with one of the first telescopes in 1610. Until he saw that they moved around Jupiter, Galileo's first thought was that they were stars. Galileo called his discoveries the Medicea Sidera ("the Medician stars"), in honour of the Medici family, who ruled Florence at the time. They were given their current names four years later. All the Galilean moons are larger than the dwarf planet Pluto, and Ganymede is larger than Mercury.



An artist's impression of what the surface of Io, with its volcanoes and lava pools, might look like. The giant globe of Jupiter...Read More >>An artist's impression of what the surface of Io, with its volcanoes and lava pools, might look like. The giant globe of Jupiter looms on the horizon.


Ganymede

Ganymede

Ganymede, at 5268 kilometres (3273 miles) across, is the largest moon in the Solar System. It also has the greatest mass of any moon, more than twice that of Earth's Moon. It is the only moon known to have its own strong magnetic field. Ganymede has an icy surface with dark, cratered plains and areas showing strange “grooved” patterns, as if someone has clawed away at its surface with a giant fork. Scientists believe there might be a water ocean about 200 kilometres (125 miles) below Ganymede's surface, trapped between layers of ice.
 
Callisto

Callisto

Galileo's discovery of the moons orbiting a world, Jupiter, other than the Earth, shattered the theory held at the time (1610) that everything in the Universe orbited around the Earth.

Q-files now has new sections specially written for younger readers. They are: Living world, Earth, Science, Human body, Prehistoric life, Space, History, Geography and Technology.


Find the answer