User login

Ganymede - Jupiter's Moon

Credit: NASA

Ganymede is the largest of Jupiter's moons and the largest in the entire Solar System. It is even larger than the planet Mercury, but only about half the mass. This means it must be much less dense. That said, it is still twice the mass of Earth's Moon.

It only takes 7 days for Ganymede to orbit Jupiter and is so large it has it's own magnetic field (tiny compared to Jupiter's)- but has no atmosphere around it.

Ganymede's surface is made up of a mixture of rock and water ice. The recent Galileo spacecraft found evidence for a saltwater ocean nearly 200 km below its surface, sandwiched between layers of ice. It is thought that there is more water in this ocean, than in all of the oceans on Earth. There is a small chance that simple forms of life may exist in that ocean.

The surface appears complicated with mountains, valleys, flat plains and craters. It also has many light and dark regions. The darker regions have more craters and so are thought to be older, with the light regions likely to be caused by recent plate movement.

Jupiter's moons - Data Sheet show »« hide
Facts and FiguresIo EuropaGanymedeCallisto
Distance from Jupiter (KM)421,600 670,9001,070,0001,883,000
Radius (KM)1,815 1,5692,6312,400
Mass (Earth Masses)0.015 0.0080.0250.018
Time of Orbit (Earth Days)1.77 3.557.1516.69
Day Length (Earth Days)1.77 3.557.1516.69


Please note that over the weekend of the 26-29th May 2017 we will be switching over to our brand new website - during this time there may be periods where the site is difficult to access, and users will be unable to request observations from the telescope. Please bear with us during this time. All should be back up and running by the 30th May 2017.