Animated image of the Juno spacecraft orbiting Jupiter. Jupiter is the largest planet in the solar system. It has a diameter of around 140, 000 kilometres, more than ten times that of Earth. It is a gas giant and is mostly hydrogen and helium. Juno arrived at Jupiter in July 2016. Its mission is to orbit Jupiter over the following year, gathering information about the planet's atmosphere, magnetic field and gravitational field. Image of Jupiter from a 1979 Voyager space probe mosaic.