However, like Jupiter, it gives off more energy than it receives from the Sun. Galileo may have seen Neptune with his rudimentary telescope in 1613, when Jupiter and Neptune were in conjunction. If indeed Galileo did observe Neptune, this would double the period of time over which it has been observed. Neptune was named after the Roman god of the sea because of its bluish colour. Above the mantle is an atmosphere of hydrogen, helium and methane gases, forming thick clouds.
Giant storms rage in the atmosphere.
Neptune has 5 faint rings and 8 moons. The largest moon, Triton, is larger than the planet Pluto. Some scientists think that millions of years ago, a large object passed close to Neptune and caused Triton to reverse its orbit, forced Nereid to go into a highly elliptical orbit, and perhaps also ejected Pluto which may at that time have been a moon of Neptune. Neptune's orbit around the Sun is nearly circular. Only Venus has a more circular orbit.