PLANET PROFILE: Neptune
Average distance from the Sun: 4, 497 million km
Orbital period: 164.8 Earth days
Orbital velocity: 5.4 km/s
Rotation period: 19.2 hours
Diameter at equator: 40, 528 km
Cloud-top temperature: -220°C
Mass: (Earth = 1) 17
Gravity (Earth = 1) 1.2
Number of moons: 8 (discovered so far)
Has/Hasn't got seasons
Discovered in 1846, Neptune is named after the mighty Roman god of the sea. It is the farthest gas planet from the Sun (4, 497 km away as mentioned above). Its atmosphere is mainly composed out of hydrogen (85%), then helium (13%). Methane creates the minority (2%). This is found in high-altitude cirrus clouds situated around 40 km above the main cloud layer.
Neptune has eight moons: Naiad (48, 000 km from planet), Thalassa (50, 000 km from planet), Despina (52, 500 km from planet), Galatea (62, 000 km from planet), Larissa (73, 600 km from planet; Larissa was a character in The Merchant of Venice by Shakespeare, coincidentally or not), Proteus (117, 600 km from planet), Triton (354, 800 km from planet), and furthest of all (5, 513, 400 km away), Nereid. Triton is, perhaps, one of the most interesting of Neptune's moons. It is the coldest place in the Solar System at -235°C. It has an atmosphere, though it is hardly anything to talk about, being very thin; it also boasts an admirable south polar ice cap composed of methane ice. Interesting evidence from photographs shows that the ice has a pinkish tinge; scientists believe this is caused by the presence of organic chemicals formed in the sunlight.
For more information, go to http://www.enchantedlearning.com/subjects/astronomy/planets/neptune/