Neptune boasts one of the most violent weather systems known. When the Voyager 2 spacecraft flew by in 1989, it discovered that winds around the planet’s equator reached speeds of 2100km/h (1240mph) — faster than anywhere else in the Solar System. Heat from inside the planet means that Neptune’s atmosphere is turbulent and constantly changing.
Neptune is the most distant planet from the Sun, with temperatures that plunge down to 55 Kelvin, or -218 degrees Celsius. You would think that a planet that cold would be frozen and locked down, with very little weather. But you’d be very wrong. In fact, the weather on Neptune is some of the most violent weather in the Solar System. Just like Jupiter and Saturn, Neptune has bands of storms that circle the planet. While the wind speeds on Jupiter can reach 550 km/hour – twice the speed of powerful hurricanes on Earth, that’s nothing compared to Neptune. Astronomers have clocked winds on Neptune traveling at 2,100 km/hour.
So why can the winds on Neptune reach such huge speeds? Astronomers think that the cold temperatures on Neptune might have something to do with that after all. The cold temperatures might decrease the friction in the system, so that winds can get going fast on Neptune.
During its 1989 flyby, NASA’s Voyager 2 spacecraft discovered the Great Dark Spot on Neptune. Similar to Jupiter’s Great Red Spot, this is an anti-cyclonic storm measuring 13,000 km x 6,600 km across. A few years later, however, the Hubble Space Telescope failed to see the Great Dark Spot, but it did see different storms. This might mean that storms on Neptune don’t last as long as they do on Jupiter or even Saturn.
The more active weather on Neptune might be due, in part, to its higher internal heat. Although Neptune is much more distant than Uranus from the Sun, receiving 40% less sunlight, temperatures on the surface of the two planets are roughly similar. In fact, Neptune radiates 2.61 times as much energy as it receives from the Sun. This is enough heat to help drive the fastest winds in the Solar System.