Neptune Facts

Discoverer(s): Galle, Challis, Adams, & Le Verrier (1846)
Spacecraft Encounter(s): Voyager 2
Mean Distance from the Sun: 30.06 AU (4.497 billion km/2.794 billion mi)
Length of year: 165 years
Rotation period: 16.11 hours
Mean orbital velocity: 5.43 km/s (3.3 mi/s)
Diameter: 49,528 km/30,775 mi
Inclination of axis: 29.6°
Number of observed satellites: 8

Comparisons with Earth:

Diameter: 3.883 x Earth's
Average distance from Sun: 30.06 x Earth's
Mass: 17.14 x Earth's
Density: 0.31 x Earth's


All information and images on this page were obtained from the National Air and Space Museum except the bottom image from NASA.

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