Triton is Neptune's largest moon and has many unique features. About the same size as Earth's moon, it has a retrograde orbit (that is, it travels in the opposite direction to the rotation of Neptune). Triton also has a large rocky core, active volcanoes and a nitrogen atmosphere. With a surface temperature of minus 235 degrees Celsius, most of the nitrogen of Triton is in the form of ice, which makes up the bulk of its cracked surface. In this false-colour image, dark streaks may represent erupted carbonaceous dust. The greenish, fissured area towards the center left is called the ‘Cantaloupe terrain’, because of its resemblance to the surface of a melon.