Uranus rolls around the Sun on its side - its axis is tipped almost 98°, probably from a colossal ancient collision. Each pole gets 42 years of continuous sunlight followed by 42 years of darkness.
Open the 3D Solar SystemUnlike Jupiter and Saturn, Uranus and Neptune are mostly water, methane and ammonia “ices” around a rocky core, wrapped in hydrogen air. Methane absorbs red light, which is why both planets look blue-green.
| Diameter | 51,118 km |
| Mass | 8.680e+25 kg |
| Surface gravity | 8.7 m/s² |
| Density | 1.27 g/cm³ |
| Rotation period | -17.24 h (retrograde) |
| Axial tilt | 97.8° |
| Mean temperature | -195 °C |
| Geometric albedo | 0.49 |
| Known moons | 29 |
| Atmosphere | About 83% H₂, 15% He and 2% methane; the methane absorbs red light, giving the planet its pale cyan colour. |
| Composition | A hot, dense fluid of water, methane and ammonia “ices” around a small rocky core, under a hydrogen-helium envelope. |
How we know: Only Voyager 2 has visited. The model rests on its flyby data plus bulk density; Uranus’s strange tilted magnetic field hints the mantle fluid is where it is generated.
| Discovered by | William Herschel |
| Year | 1781 |
| How | First planet ever found with a telescope, from his garden in Bath, England |