Specs
| What | Data |
|---|---|
| Name | Uranus |
| Class | Ice Giant (see note below) |
| Planet number | 7 |
| Diameter | 50,724 km |
| Mass | 8.681 × 10²⁵ kg (14.5× Earth) |
| Distance from the Sun | 2.87 billion km / 19.2 AU |
| Orbital period | 84 years |
| Rotation period | 17h 14m (retrograde) |
| Known moons | 28 |
| Largest moon | Titania |
The tilted planet
Uranus is the seventh planet from the Sun and the third largest. Its most unusual feature is its extreme axial tilt of about 98° — it essentially orbits the Sun on its side, so each pole spends roughly 42 years in continuous sunlight followed by 42 years of darkness. It also rotates in the opposite direction to most planets (retrograde).
Discovered by William Herschel in 1781, it was the first planet found with a telescope.
Ice giant — or magma-ocean giant?
For decades Uranus and Neptune have been classified as ice giants: a hydrogen/helium atmosphere over a vast mantle of “ices” (water, ammonia, methane) and a rocky core. A 2026 study from the University of California challenges that picture.
The researchers note the three-layer ice-giant model is not the only way to explain the planets’ properties. Objects in the Kuiper Belt — thought to preserve the material from where Uranus and Neptune formed — are mostly rock, not ice. Their best-fitting model instead suggests a well-mixed magma ocean with hydrogen dissolved into it at the bottom and a hydrogen-dominated envelope on top. At high pressure, hydrogen gas can dissolve into magma to form a single well-mixed fluid, which could explain the planets’ density without an ice-rich interior.
If correct, Uranus and Neptune might be better described as “magma-ocean giants.” The idea could also help explain the interiors of the many sub-Neptune exoplanets across the Milky Way.
Source: Scientists Think Neptune and Uranus May Not Be the Ice Giants We Imagined (Slashdot, via Gizmodo).