Which planet rotates on its side?
Quick answer
Uranus rotates on its side. Its axis is tilted about 98 degrees, so it seems to roll around the Sun like a ball rather than spin like a top. Scientists think a giant collision with an Earth-sized object knocked it over billions of years ago.
How tilted are the planets?
| Planet | Axial tilt |
|---|---|
| Mercury | ~0° |
| Venus | ~177° (upside down, spins backward) |
| Earth | 23.4° |
| Mars | 25° |
| Jupiter | 3° |
| Saturn | 27° |
| Uranus | ~98° |
| Neptune | 28° |
Extreme seasons
Uranus takes 84 Earth years to orbit the Sun. Because of its tilt, each pole spends about 42 years in continuous sunlight, followed by 42 years of darkness. Imagine a winter lasting half a lifetime.
Why it tipped over
The leading idea is that one or more huge impacts early in the solar system’s history knocked Uranus sideways. Other theories suggest the gravity of a large moon that later escaped, or interactions with other planets, slowly tilted it.
Uranus facts
- It’s an ice giant, made mostly of water, methane and ammonia ices around a rocky core.
- Methane in its atmosphere absorbs red light, giving it a blue-green color.
- It was the first planet discovered with a telescope, by William Herschel in 1781.
- It has 13 known rings and 28 known moons, many named after characters from Shakespeare and Alexander Pope.
- Only one spacecraft has visited: Voyager 2, in 1986.
The coldest atmosphere
Even though Neptune is farther from the Sun, Uranus has recorded the coldest atmospheric temperature of any planet, about −224°C, because it gives off very little internal heat.
Other planet extremes: which planet has the shortest day and which planet is the hottest.
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