Neptune
Planet
Facts
- Diameter
- 49,528 km
- Mean distance from the Sun
- 4.5 billion km
- Orbital period
- about 165 years
- Rotation
- 16.1 hours
- Axial tilt
- 28.3°
- Mean temperature
- −200 °C
Neptune is the eighth and most distant planet, 30 astronomical units from the Sun, and the windiest: clouds of frozen methane race along at more than 1900 km/h. At least 80% of its mass is a hot, dense fluid of “icy” materials. It is named after the Roman god of the sea.
It was the first planet found by mathematical prediction: Urbain Le Verrier worked out its position from irregularities in the orbit of Uranus, and Johann Gottfried Galle found it at the Berlin observatory in 1846, on the first night of searching. In 2011 it completed its first orbit since its discovery.
It has at least five main rings, named Galle, Le Verrier, Lassell, Arago and Adams, and four arcs. Its moon Triton is the only large moon in the Solar System that circles its planet in the opposite direction to the planet's rotation. In 1989 Voyager 2 saw a large oval storm in the southern hemisphere, the Great Dark Spot, which later disappeared.