Neptune (lower left) and its moon Triton (upper right). Neptune is the eighth planet from the Sun,orbiting at a distance of over 4.5 billion kilometres. It has a diameter of over 48,000 kilometres,around 3.8 times that of Earth,and a volume of around 55 Earths. It is considered an ice giant,with an icy interior and an atmosphere of hydrogen and helium. Triton,its largest moon,consists of ices and rocks. It has a diameter of around 2700 kilometres,and orbits Neptune at a distance of around 355,000 kilometres. Image obtained on 19 September 2015 |