Space Facts

Neptune Facts

Neptune is the eighth planet from the Sun making it the most distant in the solar system. This gas giant planet may have formed much closer to the Sun in early solar system history before migrating to its present position.

Neptune Planet Profile

Equatorial Diameter:49,528 km
Polar Diameter:48,682 km
Mass:1.02 × 10^26 kg (17 Earths)
Moons:14 (Triton)
Rings: 5
Orbit Distance:4,498,396,441 km (30.10 AU)
Orbit Period:60,190 days (164.8 years)
Effective Temperature: -214 °C
Discovery Date:September 23rd 1846
Discovered By:Urbain Le Verrier & Johann Galle

Neptune Diagrams

Neptune size compared to Earth

Neptune distance from the Sun and orbital eccentricity

Facts about Neptune

Neptune’s Great Dark Spot

The Great Dark Spot in the southern atmosphere of Neptune was first discovered in 1989 by the Voyager 2 spacecraft. It was an incredibly large rotating storm system with winds of upto 1,500 miles per hour, the strongest winds recorded on any planet. How such powerful winds were discovered on a planet so far from the sun is still considered a mystery to this day.

Data from the Voyager 2 spacecraft also showed that the Great Dark Spot varied significantly in size during their brief pass of the planet. When Neptune was viewed by the Hubble Space telescope in 1994 the Great Dark Spot had vanished, although a different dark spot had appeared in Neptune’s northern hemisphere.

Neptune’s Atmosphere

Neptune has an incredibly thick atmosphere comprised of 74% hydrogen, 25% helium and approximately 1% methane. Its atmosphere also contains icy clouds and the fastest winds recorded in the solar system. Particles of icy methane and minor gases in the extremities of the atmosphere give Neptune its deep blue colour. The striking blue and white features of Neptune also help to distinguish it from Uranus.

Neptune’s atmosphere is subdivided into the lower troposphere and the stratosphere with the tropopause being the boundary between the two. In the lower troposphere temperatures decrease with altitude however they increase with altitude in the stratosphere. Hydrocarbons form hazes of smog that appear in the entire upper atmosphere of Neptune and hydrocarbon snowflakes that form in Neptune’s atmosphere melt before they reach its surface due to the high pressure.