Ganymede is the biggest moon in the entire solar system. It is the moon of Planet Jupiter. Ganymede was discovered in 1610 by astronomer Galileo Galilei. Ganymede’s distance from Jupiter is 1,070,400 kilometres. This moon has a number of layers. Ganymede is without a substantial atmosphere containing oxygen, but not enough to support life. Ganymede is the only moon that generates a strong magnetic field. It has a diameter of 5,268 kilometres and is 8 per cent larger than the planet Mercury, although only 45 per cent as massive.