which although quite cold, are hotter than one would expect given the planetΓÇÖs distance from the Sun. Thus, astronomers believe that Neptune, unlike Uranus, is heated by an internal source. This source, whatever it may be, causes the somewhat higher temperatures in the atmosphere as well.
Neptune has both moons and a ring system. The ring system is quite thin and likely has the least mass of all the outer planets. Two of the planetΓÇÖs eight moons were known from Earth observations; six additional ones were discovered by Voyager 2. The largest, Triton, is about the size of the EarthΓÇÖs Moon and is one of the few moons to show evidence of possessing an atmosphere.
