The line, Then felt I like some watcher of the skies

In 1986, NASA's Voyager 2 interplanetary probe encountered Uranus. This flyby remains the only investigation of the planet carried out from a short distance, and no other visits are currently planned. Launched in 1977, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers of Uranus's cloudtops, before continuing its journey to Neptune. Voyager 2 studied the structure and chemical composition of Uranus's atmosphere,[69] including its unique weather, caused by its axial tilt of 97.77°. It made the first detailed investigations of its five largest moons, and discovered 10 new moons. It examined all nine of the system's known rings and discovered two new ones.[16][83][122] It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.[91]

The possibility of sending the Cassini spacecraft to Uranus was evaluated during a mission extension planning phase in 2009.[123] It would take about twenty years to get to the Uranian system after departing Saturn.[123] A Uranus orbiter and probe was recommended by the 2013–2022 Planetary Science Decadal Survey published in 2011; the proposal envisages launch during 2020–2023 and a 13-year cruise to Uranus.[124] A Uranus entry probe could use Pioneer Venus Multiprobe heritage and descend to 1–5 atmospheres.[124] The ESA evaluated a "medium-class" mission called Uranus Pathfinder.[125] A New Frontiers Uranus Orbiter has been evaluated and recommended in the study, The Case for a Uranus Orbiter.[126] Such a mission is aided by the ease with which a relatively big mass can be sent to the system—over 1500 kg with an Atlas 521 and 12-year journey.[127] For more concepts see Proposed Uranus missions.

In culture

In astrology, the planet Uranus (Uranus's astrological symbol.svg) is the ruling planet of Aquarius. Since Uranus is colored cyan and Uranus is associated with electricity, the color electric blue, a color close to cyan, is associated with the sign Aquarius.[128] (See Uranus in astrology)

The chemical element uranium, discovered in 1789 by the German chemist Martin Heinrich Klaproth, was named after the newly discovered planet Uranus.[129] Uranus, the Magician is a movement in Gustav Holst's The Planets, written between 1914 and 1916. Operation Uranus was the successful military operation in World War II by the Soviet army to take back Stalingrad and marked the turning point in the land war against the Wehrmacht.

The line, Then felt I like some watcher of the skies/When a new planet swims into his ken, from John Keats's On First Looking Into Chapman's Homer is a reference to Herschel's discovery of Uranus

Uranus possesses at least one horseshoe orbiter occupy

Many argue that the differences between the ice giants and the gas giants extend to their formation.[111][112] The Solar System is believed to have formed from a giant rotating ball of gas and dust known as the presolar nebula. Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, while the dust grains collected together to form the first protoplanets. As the planets grew, some of them eventually accreted enough matter for their gravity to hold onto the nebula's leftover gas.[111][112] The more gas they held onto, the larger they became; the larger they became, the more gas they held onto until a critical point was reached, and their size began to increase exponentially. The ice giants, with only a few Earth masses of nebular gas, never reached that critical point.[111][112][113] Recent simulations of planetary migration have suggested that both ice giants formed closer to the Sun than their present positions, and moved outwards after formation, a hypothesis which is detailed in the Nice model
Uranus has 27 known natural satellites.[113] The names for these satellites are chosen from characters from the works of Shakespeare and Alexander Pope.[57][114] The five main satellites are Miranda, Ariel, Umbriel, Titania and Oberon.[57] The Uranian satellite system is the least massive among the gas giants; indeed, the combined mass of the five major satellites would be less than half that of Triton alone.[9] The largest of the satellites, Titania, has a radius of only 788.9 km, or less than half that of the Moon, but slightly more than Rhea, the second largest moon of Saturn, making Titania the eighth largest moon in the Solar System. The moons have relatively low albedos; ranging from 0.20 for Umbriel to 0.35 for Ariel (in green light).[16] The moons are ice–rock conglomerates composed of roughly fifty percent ice and fifty percent rock. The ice may include ammonia and carbon dioxide.[83][115]

Among the satellites, Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest.[16][83] Miranda possesses fault canyons 20 kilometers deep, terraced layers, and a chaotic variation in surface ages and features.[16] Miranda's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently, probably as a result of a formerly present 3:1 orbital resonance with Umbriel.[116] Extensional processes associated with upwelling diapirs are the likely origin of the moon's 'racetrack'-like coronae.[117][118] Similarly, Ariel is believed to have once been held in a 4:1 resonance with Titania.[119]

Uranus possesses at least one horseshoe orbiter occupying the Sun–Uranus L3 Lagrangian point – a gravitationally unstable region at 180º in its orbit, 83982 Crantor.[120][121] Crantor currently moves inside Uranus's co-orbital region on a complex, temporary horseshoe orbit. 2010 EU65 is also a promising Uranus horseshoe librator candidate