Solar Exploration

Neptune is the most distant planet in the solar system, orbiting the Sun at over four and a half billion kilometers — so far that sunlight takes about four hours to reach it, compared to roughly eight minutes for Earth. Despite that distance, Neptune is dynamically the stormiest planet known, with the fastest winds recorded anywhere in the solar system, reaching speeds of up to 2,100 km/h.

Neptune's deep blue color, even more vivid than Uranus's, comes from methane in its atmosphere absorbing red light. Its largest moon, Triton, is unusual among large moons for orbiting backwards relative to Neptune's rotation, strong evidence that Triton wasn't born alongside Neptune but was instead captured from the Kuiper Belt — the same distant region of icy bodies that includes Pluto.

Neptune's atmosphere shows dark storm systems similar to Jupiter's Great Red Spot, including a feature nicknamed the Great Dark Spot observed by Voyager 2 in 1989 that had vanished by the time the Hubble Space Telescope looked again just a few years later — a reminder that these giant storms can form and dissipate on surprisingly short timescales. Beneath the visible atmosphere lies a hot, dense fluid mantle of water, ammonia and methane surrounding a rocky core roughly Earth's size.