Uranus
Ice Giant
Distance from Sun
2.871 B km
Orbital Period
84.01 years
About Uranus
Uranus is the seventh planet from the Sun and the first to be discovered with a telescope, found by William Herschel in 1781. Classified as an ice giant, Uranus differs from the gas giants Jupiter and Saturn in that its bulk composition includes significant amounts of heavier volatile substances such as water, ammonia, and methane ices, in addition to hydrogen and helium.
The planet's most striking characteristic is its extreme axial tilt of about 98 degrees, meaning it essentially orbits the Sun rolling on its side. This extraordinary tilt, likely the result of a cataclysmic collision with an Earth-sized body during the early solar system, gives Uranus the most extreme seasons of any planet. Each pole gets around 42 years of continuous sunlight followed by 42 years of darkness.
Uranus appears as a nearly featureless pale cyan sphere, its color coming from methane in the atmosphere, which absorbs red light and reflects blue-green wavelengths. Beneath its deceptively calm exterior, however, the planet experiences powerful winds and possesses a complex magnetic field that is tilted 59 degrees from its axis of rotation and offset from the planet's center.
Key Facts
- Uranus is tilted 98 degrees on its axis, likely due to a collision with an Earth-sized protoplanet billions of years ago.
- It is the coldest planetary atmosphere in the solar system, with a minimum temperature of -224 °C, colder even than Neptune despite being closer to the Sun.
- Uranus has 13 known rings, which are dark and narrow compared to Saturn's bright, wide rings. They were discovered in 1977.
- The planet's magnetic field is uniquely off-center, tilted 59 degrees from its rotational axis and offset from the planet's core by one-third of the planet's radius.
- Wind speeds on Uranus can reach up to 900 km/h, though the planet appears deceptively calm from a distance.
- All 28 of Uranus's known moons are named after characters from the works of William Shakespeare and Alexander Pope.
- Uranus was originally named "Georgium Sidus" (George's Star) by Herschel in honor of King George III before being renamed.
Exploration History
Voyager 2 (1986)
The only spacecraft to visit Uranus. Flew within 81,500 km, discovering 10 new moons, 2 new rings, and a surprisingly tilted magnetic field.
Hubble Space Telescope (1990s-present)
Has provided detailed observations of Uranus's atmosphere, rings, and moons from Earth orbit, revealing seasonal changes and new cloud features.
James Webb Space Telescope (2023)
Captured stunning near-infrared images revealing Uranus's rings, moons, and atmospheric features in unprecedented detail.
Uranus Orbiter & Probe (proposed)
Recommended as the highest-priority flagship mission in the 2023-2032 Planetary Science Decadal Survey. Would study the ice giant system in depth with an orbiter and atmospheric probe.
Deep inside Uranus, extreme pressure may crush carbon atoms into diamonds that rain down through the mantle like hailstones. Scientists have recreated these conditions in labs and confirmed that "diamond rain" is physically plausible inside ice giants. These diamond deposits may form a thick layer around the planet's rocky core.