The planet Jupiter, showing two of its moons and the Great Red Spot, 1979

The planet Jupiter, showing two of its moons and the Great Red Spot, 1979. Taken from 20 million kilometres away by Voyager 1, this picture shows the Great Red Spot, and two of Jupiter's four main moons; Io, which is above the Great Red Spot, and Europa. NASA launched two Voyager spacecraft in 1977 to explore the planets in the outer solar system. Voyager 1 flew past Jupiter at 278,000 kilometres in March 1979 before going on to pass Saturn in 1980. The largest planet in the solar system, Jupiter is a type of planet known as a gas giant, with an atmosphere composed mainly of hydrogen and helium. The atmosphere contains a number of large storms, the most famous of which, the Great Red Spot, is larger than the Earth and has been in existence for at least 300 years. ©SSPL/NASA