The 4 largest of Jupiter's moons which can easily be seen through binoculars are IO, Europa, Ganymede and Callisto. They are known collectively as the Galilean satellites because they were discovered in 1610 by the Italian Galileo Galilei. Jupiter holds the most and largest satellites in the solar system with some bigger than the planets Mercury and Pluto. Unfortunately none seem to be habitable as they all lack an atmosphere but one day when the Sun increases in size sucking in Jupiter’s Hydrogen, some may fall on its satellites and the gravitational pull of Jupiter’s moons may be able to keep hold of the new atmosphere making them habitable.

GANYMEDE
This is the largest of Jupiter’s moons; it is made up of rock and ice. This moon has been subjected to ice faulting and ice flows. Whereas the dark areas on the moon are younger rocks, on Ganymede the darker areas are older.

CALLISTO
Callisto is next to Ganymede on the picture above. Callisto is like Ganymede in the sense it is made up of rock and ice but it lacks internal activity so does not show evidence of faulting.

IO
IO appears yellow and orange because of the huge quantities of sulphur deposits that cover its surface. IO is covered with volcanic vents causing the black spots seen on the image. It is the most volcanically active body in the solar system, the reason for this is due to the other Galilean satellites which repeatedly squeeze it, releasing frictional heat which melts its interior.

EUROPA
This is the smallest of the Galilean satellites and is encased by a bright icy shell. Scientists believe that under the icy surface there may be an ocean of liquid water, in this ocean life could exist because we know from Earth that life can live without sunlight. On Earth bacteria has been found to live in extreme conditions such as living near to under water volcanic vents.