Uranus

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**Uranus** is the seventh planet from **the Sun** and is a gaseous cyan ice giant. Most of Uranus is made out of water, ammonia, and methane in a

## Orbit Data

### Orbital Period

(Sidereal)
84.0205 yr
30,688.5 d
42,718 Uranian solar days
(Synodic)
369.66 d

### Inclination

0.773° to ecliptic
6.48° to Sun's equator
0.99° to invariable plane

## Physical Characteristics

### Synodic Rotation Period

−0.71832 d
−17 h 14 m 23 s
(retrograde)

### Sidereal Rotation Period

−0.71833 d
−17 h 14 min 24 s
(retrograde)

## Atmospheric Data

### Composition

Below 1.3 bar (130 kPa):
83 ± 3% hydrogen
15 ± 3%
helium
2.3% methane
0.009% (0.007–0.015%)
hydrogen deuteride
hydrogen sulfide (trace amount)
Icy volatiles: ammonia,water ice,ammonium hydrosulfide,methane hydrate

supercritical phase of matter, which in astronomy is called 'ice' or volatiles. The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature of 49 K (−224 °C; −371 °F) out of all Solar System's planets. Uranus has a marked axial tilt of 97.8° with a retrograde rotation rate of 17 hours. This means that in an 84 Earth years orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness.

Uranus has the third-largest diameter and fourth-largest mass among the Solar System's planets. Based on current models, inside Uranus's volatile mantle layer is a rocky core, and surrounding it is a thick hydrogen and helium atmosphere. Trace amount of hydrocarbons (thought to be produced via hydrolysis) and carbon monoxide along with carbon dioxide (thought to have been originated from comets) have been detected in the upper atmosphere. There are many unexplained climate phenomena in Uranus's atmosphere, such as its peak wind speed of 900 km/h (560 mph), variations in its polar cap and its erratic cloud formation. Uranus also has a very low internal heat compared to other giant planets, which is still unexplained.

Like the other giant planets, Uranus has a ring system, orbiting natural satellites and a magnetosphere. Uranus's ring system is extremely dark, with only about 2% of the incoming light is reflected, and contains the known 13 inner moons. Further out are the larger 5 major moons of the planet: Miranda, Ariel, Umbriel, Titania, and Oberon; and orbit at much greater distance from Uranus are the known 9 irregular moons. Uranus magnetosphere is highly asymmetric and has many charged particles, which may cause the darkening of its rings and moons.

Uranus is visible to the naked eye, but it is very dim and was not classified as a planet until 1781, when it was first observed by William Herschel. About seven decades after its discovery, consensus was reached that the planet be named from the Greek god Uranus (Ouranos), one of the Greek primordial deities. As of 2023, Uranus was visited up close only one time when in 1986 the *Voyager 2* probe flew by the planet. Though nowadays Uranus can be resolved and observed by telescopes, there is much desire to revisit the planet, as shown by Planetary Science Decadal Survey's decision to make the proposed Uranus Orbiter and Probe mission a top priority in the 2023–2032 survey.