PlanetSolar system

Neptune

A deep-blue ice giant at the edge of the planetary Solar System, where supersonic winds tear across a world we have visited only once.

Ice giant · 30.1 AU from the Sun · 164.8-year orbit · 16 known moons

Planet type
Ice giant
Mean radius
24,622 km
Distance from the Sun
30.1 AU · 4.50 billion km
Day length
16 h 6 min
Orbital period
164.8 Earth years
Peak wind speed
About 2,000 km/h
Cloud-top temperature
About −200 °C
Confirmed moons
16

The windiest world

Neptune is the farthest planet from the Sun in the Solar System. It is similar in size to Uranus but more massive, with a deeper blue color and a much more active atmosphere. Winds in its upper atmosphere can exceed 2,000 km/h — the fastest measured on any planet.

Its atmosphere is mostly hydrogen and helium, with methane contributing the blue tint. Despite receiving only about 0.1% of the sunlight Earth gets, Neptune drives large storms and cloud activity through internal heat and atmospheric dynamics.

Dark spots and Triton

Voyager 2 discovered a Great Dark Spot during its 1989 flyby. Later Hubble observations found other dark vortices that appear and disappear over years. JWST is now following these storms in infrared light and studying Neptune’s clouds and upper atmosphere in new detail.

Neptune’s largest moon, Triton, orbits backwards and is thought to be a captured Kuiper Belt object. Its icy surface shows geysers, cantaloupe terrain, and evidence of past cryovolcanism, making it one of the most intriguing moons in the Solar System.

A real view of Neptune

NASA/JPL · Voyager 2
Voyager 2 image of Neptune showing its deep blue atmosphere
Neptune from NASA’s Voyager 2, assembled from the last whole-planet images taken through green and orange filters. Image: NASA/JPL.

Voyager 2 and JWST

Voyager 2 remains the only spacecraft to visit Neptune, flying past in 1989. JWST has since given us a new view of the planet’s atmosphere and its small satellites, while future mission concepts aim to return to the Neptune system.

  • What drives Neptune’s extreme winds?
  • How do its dark spots form and decay?
  • How did Triton become a moon of Neptune?
  • Is there a subsurface ocean beneath Triton’s ice?

Recent publications

YearPaperJournalLink
2026The Complete Life Cycle of Dark Spot NDS-2018 on NeptuneGeophysical Research LettersDOI
2024JWST Spectrophotometry of the Small Satellites of Uranus and NeptunePlanetary Science JournalDOI
2023Spectral determination of the colour and vertical structure of dark spots in Neptune’s atmosphereNature AstronomyDOI
2026A modern dynamo at Triton as a consequence of its capture by NeptuneNature AstronomyDOI
2024Triton’s Captured Youth: Tidal Heating Kept Triton Warm and ActivePlanetary Science JournalDOI

Compiled 20 October 2026. Links resolve to the publisher DOI record.