Which planet has the Great Dark Spot?
Quick answer
The Great Dark Spot was a huge storm on Neptune, photographed by NASA’s Voyager 2 spacecraft during its flyby in August 1989. The dark oval was roughly the size of Earth. When the Hubble Space Telescope looked in 1994, it had disappeared, though new dark spots have appeared since then.
A storm that came and went
| Year | Observation |
|---|---|
| 1989 | Voyager 2 photographs the Great Dark Spot in Neptune’s southern hemisphere |
| 1994 | Hubble finds it gone, and a new dark spot in the northern hemisphere |
| 2018 onward | Hubble tracks more dark spots forming and fading |
Unlike Jupiter’s Great Red Spot, which has lasted for centuries, Neptune’s dark spots seem to last only a few years. Scientists think they’re high-pressure storms that drift toward the equator and break apart. Bright white clouds, nicknamed “Scooter,” often form near them.
The windiest planet
Neptune has the fastest winds measured in the solar system, reaching about 2,100 km/h (1,300 mph), faster than the speed of sound on Earth. That’s surprising for a planet so far from the Sun, and its internal heat likely helps drive them.
Neptune at a glance
| Fact | Value |
|---|---|
| Distance from the Sun | About 4.5 billion km (30 times Earth’s) |
| Year | About 165 Earth years |
| Day | About 16 hours |
| Diameter | About 4 times Earth’s |
| Moons | 16 known; the largest is Triton |
| Color | Blue, from methane in its atmosphere |
Triton orbits backward, opposite to Neptune’s spin, suggesting it was a captured object from the Kuiper Belt; see what the Kuiper Belt is.
Found with mathematics
Neptune is the only planet found by prediction before being seen. Astronomers noticed Uranus wasn’t moving as expected. French mathematician Urbain Le Verrier calculated where an unseen planet should be, and German astronomer Johann Galle spotted Neptune there on September 23, 1846. Uranus has its own oddity; see which planet rotates on its side.
Voyager 2’s grand tour
Voyager 2 is the only spacecraft to have visited Uranus and Neptune. Launched in 1977, it’s now in interstellar space, more than 20 billion km from Earth.
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