Neptune Fact File

The Planet Neptune
At a distance of 4.5 billion kilometers from the sun, Neptune completes its orbit once every 165 years. Due to Pluto's unusual elliptical orbit, Neptune is actually the farthest planet from the Sun for a 20-year period out of every 248 Earth years.

Neptune is the smallest of our solar system's giant gas planets (including Jupiter, Saturn, and Uranus). Neptune's atmosphere extends to great depths, gradually merging into water and other "melted ices" over a heavier, liquid core. Neptune's rotational axis is tilted 30 degrees to the plane of its orbit around the Sun. Its seasons last an incredible 41 years. During the southern summer, the south pole is in constant sunlight for about 41 years, and in northern summer, the north pole is in constant sunlight for about 41 years. Neptune's atmosphere is made up of hydrogen, helium, and methane, the last of these giving the planet its blue color.

The planet has several rings of varying widths. Neptune's rings are believed to be relatively young and relatively short-lived. Neptune has 13 known moons, six of which were discovered by Voyager 2. The largest, Triton, orbits Neptune in a direction opposite to the planet's rotation direction, and is gradually getting closer until it will collide with the planet in about 10 to 100 million years, forming vast rings around Neptune that will rival or exceed Saturn's extensive ring system. With surface temperatures of about -235 °C Triton is the coldest body yet visited in our solar system.

Neptune: Facts & Figures

  • Average Distance from the Sun: 4,498,252,900 km
  • Perihelion (closest): 4,459,630,000 km
  • Aphelion (farthest): 4,536,870,000 km
  • Equatorial Radius: 24,764 km
  • Equatorial Circumference: 155,597 km
  • Mass: 102,440,000,000,000,000,000,000,000 kg
  • Volume: 62,526,000,000,000 km3
  • Density: 1.76 g/cm3
  • Surface Area: 7,640,800,000 km2
  • Equatorial Surface Gravity: 10.71 m/s2
  • Escape Velocity: 85,356 km/h
  • Length of Day: 16.11 hours
  • Length of Year: 60,190 Earth days (164.79 Earth years)
  • Mean Orbit Velocity: 19,720 km/h
  • Orbital Eccentricity: .00859
  • Orbital Inclination to Ecliptic: 1.769 degrees
  • Equatorial Inclination to Orbit: 29.58 degrees
  • Orbital Circumference: 28,142,000,000 km
  • Effective Temperature: -214 °C
  • Atmospheric Constituents: Hydrogen, Helium, Methane
  • Number of Moons: 13

Source: NASA