Neptune

The fastest winds in the solar system

Neptune is the most distant planet, receiving only a tiny fraction of the sunlight Earth gets, yet its weather is the most violent we know. Winds in its upper atmosphere blow at more than 2,000 km/h, faster than the speed of sound on Earth and stronger than any hurricane on our planet.

Scientists are still working out how such a cold, dim world can drive winds this powerful. Part of the answer is that Neptune gives off more than twice as much heat as it receives from the Sun, and with no solid surface to create friction, the winds can build to extreme speeds.

Storms that come and go

When Voyager 2 flew past in 1989, it spotted a giant storm about the size of Earth, nicknamed the Great Dark Spot, along with bright white clouds of methane ice racing around the planet. A few years later, Hubble looked again and the Great Dark Spot had vanished.

Since then Hubble has watched several new dark storms form and fade, showing that Neptune's weather is surprisingly changeable. Its deep blue color comes from methane gas absorbing red light, plus a haze that is thinner than the one on Uranus.

Found with mathematics

Neptune is the only planet discovered by prediction rather than by chance. In the 1840s, astronomers noticed that Uranus was drifting from its expected path, as if something unseen was tugging on it. Urbain Le Verrier calculated where that mystery planet should be, and on September 23, 1846, Johann Galle found Neptune within about a degree of the predicted spot.

Neptune takes about 165 Earth years to orbit the Sun, so it completed its first full orbit since discovery only in 2011.

Neptune is the eighth and farthest planet from the Sun, about 30 times farther out than Earth. At that distance, sunlight takes roughly four hours to arrive, and from Neptune's cloud tops the Sun would look like an extremely bright star rather than a disk. It cannot be seen with the naked eye from Earth.

Triton, the backward moon

Neptune has 16 known moons, but one dominates. Triton orbits in the opposite direction to Neptune's spin, a strong sign that it was once a dwarf planet from the Kuiper Belt that Neptune captured. Voyager 2 saw dark plumes rising from its frozen nitrogen surface, making it one of the coldest active worlds known.

Neptune also has faint, clumpy rings. Voyager 2 remains the only spacecraft to visit, and today the James Webb Space Telescope shows those rings more clearly than at any time since that 1989 flyby.

← UranusPluto →