Uranus

Planet· orbits the Sun

Uranus is the seventh planet — an ice giant that rotates on its side, tipped 98° so its poles take turns facing the Sun. Methane gives it a pale cyan colour.

Open in 3D viewSee Uranus in the live, interactive 3D map

Key facts

Mass

8.68 × 10²⁵ kg

14.5 M⊕

Radius

25,362 km

3.98× wider than Earth

Surface gravity

9.01 m/s²

92% of Earth's gravity

Day length

17.24 hours

Year

84 Earth years

30,685 Earth days

Distance from Sun

19.3 AU

Moons

known, incl. provisional (JPL SSD)

Science

Physical

Mass: 8.68 × 10²⁵ kg · 14.5 M⊕
Radius: 25,362 km · 3.98× wider than Earth
Density: 1,270 kg/m³ · 1.3× water; Computed from mass and radius
Surface gravity: 9.01 m/s² · 92% of Earth's gravity; Computed from mass and radius
Escape velocity: 21.4 km/s · 1.91× Earth's escape velocity; Computed from mass and radius
Axial tilt: 97.77 °

Orbital

Distance from the Sun: 19.4 AU; Computed from the position at the selected time
Semi-major axis: 19.3 AU; Computed from the cached state vector
Eccentricity: 0.04756; Computed from the cached state vector
Inclination: 23.66 °; Computed from the cached state vector
Orbital period: 84.54 years; Computed from the cached state vector
Perihelion: 18.3 AU; Computed from the orbital elements
Aphelion: 20.2 AU; Computed from the orbital elements
Mean orbital velocity: 6.79 km/s; Computed from the orbital elements

Rotation

Rotation period: 17.24 hours
Direction: Retrograde

Atmosphere

Composition: 83% H₂, 15% He, 2.3% CH₄
Scale height: 27.7 km

Rings

Composition & structure: Dark, low-albedo particles — as dark as charcoal (geometric albedo ~0.03): water ice mixed with a radiation-processed, carbon-rich (organic) component. The main narrow rings (notably ε) are made mostly of centimetre-to-metre boulders with very little dust; the outer ν and μ rings are the dusty exception. Established from Voyager 2 (1986) and Hubble/ground-based observation. The precise chemistry of the dark carbon-bearing component is not established — that is the genuine open question.

Temperature

Mean: 76 K (-197 °C)

Composition

Bulk composition: Still debated — usually modelled as water, ammonia and methane ices over a rocky core, but models with far more rock fit the same measurements

Radiation & temperature

Insolation: 0.0027 S⊕ · 1/371 of the sunlight Earth receives; Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Bond albedo: 0.30 · reflects 30% of incoming sunlight
Equilibrium temperature: 58 K (-215 °C); Computed from albedo + distance from the Sun (airless black body)
Measured mean temperature: 76 K (-197 °C)
Greenhouse warming: +18 K; Measured temperature minus the airless equilibrium — the greenhouse effect
Surface magnetic field: 23 µT · 46% of Earth's magnetic field

Discovery & history

Discovered: March 13, 1781
By: William Herschel
Method: Visual discovery (telescopic)
Name: The Greek god of the sky, Ouranos — father of Saturn (Cronus).

Uranus was the first planet discovered with a telescope. On 13 March 1781 William Herschel, surveying the sky from his garden in Bath, England, noticed a 'curious' object that he first took for a comet. Tracking its slow, near-circular orbit revealed a new planet, doubling the size of the known Solar System overnight. Herschel wanted to name it 'Georgium Sidus' after King George III; the name Uranus, proposed by Johann Bode, eventually won out. Voyager 2 remains the only spacecraft to have visited it, in 1986.

1986Voyager 2Flyby
The first and only close visit to Uranus — found ten new moons and two new rings, and a magnetic field bizarrely tilted 59° and offset from the planet's centre.