Ice Giant · Updated May 2026
Neptune.
Neptune is the eighth and farthest planet from the Sun, a deep-blue ice giant with the strongest sustained winds of any planet — up to 2,100 km/h. Its 49,244 km diameter is roughly four times Earth's. At an average 4.5 billion km from the Sun, sunlight there is just 1/900 as bright as on Earth, and a single Neptunian year takes 164.8 Earth years. It has 16 known moons, including Triton, which orbits backwards and is likely a captured Kuiper Belt object.
Open Neptune in the viewer →Key facts
Neptune was the first planet discovered through mathematical prediction rather than direct observation. Urbain Le Verrier and John Couch Adams independently calculated where it should be from anomalies in Uranus's orbit; Johann Galle found it in 1846 within one degree of the predicted position. In the viewer, watch how slowly Neptune crawls — it has only completed one full orbit since its discovery.
Atmosphere
80% hydrogen, 19% helium, 1% methane. The deeper blue compared to Uranus comes partly from methane and partly from an unidentified additional absorber. Voyager 2 saw a Great Dark Spot in 1989 — a storm the size of Earth that had vanished by the time Hubble imaged the planet five years later.
Surface
No solid surface. The atmosphere transitions smoothly into a supercritical fluid mantle of water, methane, and ammonia.
Interior
Rocky core, hot dense mantle of supercritical "ices," gas envelope. Unlike Uranus, Neptune radiates 2.6× the energy it receives — a residual heat output similar to Jupiter's.
Formation
Likely formed closer in and migrated outward during the early solar system's reorganization (the Nice Model). That migration also scattered icy bodies into the Kuiper Belt and Oort Cloud.
Orbit
Average distance from the Sun: 4.50 billion km (30.07 AU). Orbital period 164.8 Earth years. Discovered 1846; has not yet completed a full orbit since its discovery (next return: 2011 was the first, the next will be 2175).
Major moons
- Triton — Triton is the only large moon with a retrograde orbit. It was likely captured from the Kuiper Belt and has active geysers.
- Nereid — Nereid has one of the most eccentric orbits of any moon, suggesting it was captured.
Notable missions
- Voyager 2 (1989 · Past flyby) — The only spacecraft ever to visit Neptune. As with Uranus, every modern view of the planet derives from that one encounter.
- Neptune Odyssey (Proposed 2030s · Concept) — A flagship Neptune orbiter and Triton probe under study.
How to view Neptune in 3D
This page is part of an interactive 3D solar system viewer built with Three.js, WebGL 2.0, and custom GLSL shaders. Neptune orbits the Sun in real time alongside every other planet, with adjustable time speed, scale sliders, and a fly mode that lets you pilot a spacecraft between bodies under realistic gravity.
Fly to Neptune now →Frequently asked questions
Why is Neptune blue?
Methane in the upper atmosphere absorbs red light. An additional unidentified absorber makes Neptune deeper blue than Uranus.
How fast are Neptune's winds?
Up to 2,100 km/h — the fastest in the solar system.
How long is a year on Neptune?
164.8 Earth years.
Sources & methodology
Numbers cross-referenced with the sources below; surface and atmosphere descriptions reflect findings as of May 2026. Renderings in the 3D viewer use textures based on Solar System Scope and NASA imagery.