NEPTUNE
Numbers
Type: Ice giant
Size (diameter): 49,244 km, or about 4 Earths
Mass: 1.0 × 1026 kg, or about 17 Earths
Length of a year (orbital period): 165 years
Number of moons: 14
Average distance from the Sun: 4.5 billion km
Temperature between: -218 and -200 degrees Celsius
Historical Review
The ice giant Neptune was the first planet located through mathematical calculations. Using predictions made by Urbain Le Verrier, Johann Galle discovered the planet in 1846. The planet is named after the Roman god of the sea, as suggested by Le Verrier.
Atmosphere
Neptune's atmosphere is made up mostly of hydrogen and helium with just a little bit of methane. Neptune's neighbor Uranus is a blue-green color due to such atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color.