Neptune Facts
- Neptune is the outermost of the four gas giants: Jupiter, Saturn, Uranus, Neptune.
- Because of its distance from the Sun, Neptune's atmosphere is a frigid -225° C (-373° F).
- The blue-green color of the planet is due to the presence of methane in the atmosphere. The atmosphere consists mostly of hydrogen, helium and methane.
- Until the Voyager encounter in 1989, the rings surrounding Neptune were thought to be arcs. We now know that the rings completely circle the planet, but the thickness of each ring varies along its length.
| 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 |
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Comparisons with Earth: |
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| 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.