Uranus

* horseshoe orbit. 2010 EU65 is also a promising Uranus horseshoe librator candidate.

## Rings

Main article: Rings of Uranus
The Uranian rings are composed of extremely dark particles, which vary in size from micrometres to a fraction of a metre. Thirteen distinct rings are presently known, the brightest being the ε ring. All except two rings of Uranus are extremely narrow – they are usually a few kilometres wide. The rings are probably quite young; the dynamics considerations indicate that they did not form with Uranus. The matter in the rings may once have been part of a moon (or moons) that was shattered by high-speed impacts. From numerous pieces of debris that formed as a result of those impacts, only a few particles survived, in stable zones corresponding to the locations of the present rings.

William Herschel described a possible ring around Uranus in 1789. This sighting is generally considered doubtful, because the rings are quite faint, and in the two following centuries none were noted by other observers. Still, Herschel made an accurate description of the epsilon ring's size, its angle relative to Earth, its red colour, and its apparent changes as Uranus travelled around the Sun. The ring system was definitively discovered on 10 March 1977 by James L. Elliot, Edward W. Dunham, and Jessica Mink using the Kuiper Airborne Observatory. The discovery was serendipitous; they planned to use the occultation of the star SAO 158687 (also known as HD 128598) by Uranus to study its atmosphere. When their observations were analysed, they found that the star had disappeared briefly from view five times both before and after it disappeared behind Uranus. They concluded that there must be a ring system around Uranus. Later they detected four additional rings. The rings were directly imaged when *Voyager 2* passed Uranus in 1986. *Voyager 2* also discovered two additional faint rings, bringing the total number to eleven.

In December 2005, the Hubble Space Telescope detected a pair of previously unknown rings. The largest is located twice as far from Uranus as the previously known rings. These new rings are so far from Uranus that they are called the "outer" ring system. Hubble also spotted two small satellites, one of which, Mab, shares its orbit with the outermost newly discovered ring. The new rings bring the total number of Uranian rings to 13. In April 2006, images of the new rings from the Keck Observatory yielded the colours of the outer rings: the outermost is blue and the other one red. One hypothesis concerning the outer ring's blue colour is that it is composed of minute particles of water ice from the surface of Mab that are small enough to scatter blue light. In contrast, Uranus's inner rings appear grey.

## Exploration

Main article: Exploration of Uranus
link=https://en.m.wikipedia.org/wiki/File:Uranus\_seen\_from\_Saturn\_by\_Cassini.jpg|alt=|thumb|Uranus as seen from the *Cassini* spacecraft at Saturn
Launched in 1977, *Voyager 2* made its closest approach to Uranus on 24 January 1986, coming within 81,500 km (50,600 mi) of the cloudtops, before continuing its journey to Neptune. The spacecraft studied the structure and chemical composition of Uranus's atmosphere, 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 ones. Voyager 2 examined all nine of the system's known rings and discovered two more. It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.

No other spacecraft has flyby Uranus since then, though there has been many proposed missions to revisit the Uranus system. The possibility of sending the *Cassini* spacecraft from Saturn to Uranus was evaluated during a mission extension planning phase in 2009, but was ultimately rejected in favour of destroying it in the Saturnian atmosphere, as it would have taken about twenty years to get to the Uranian system after departing Saturn. A Uranus entry probe could use Pioneer Venus Multiprobe heritage and descend to 1–5 atmospheres. 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. The committee's opinion was reaffirmed in 2022, when a Uranus probe/orbiter mission placed was placed at the highest priority, due to the lack of knowledge about ice giants.

## In culture

* In astrology, the planet Uranus (symbol https://upload.wikimedia.org/wikipedia/commons/thumb/2/29/Uranus\_monogram.svg/22px-Uranus\_monogram.svg.png) is the ruling planet of Aquarius. Because Uranus is cyan and Uranus is associated with electricity, the colour electric blue, which is close to cyan, is associated with the sign Aquarius (see Uranus in astrology).
* The chemical element uranium, discovered in 1789 by the German chemist Martin Heinrich Klaproth, was named after the then-newly discovered Uranus.
* Lydia Sigourney included her poem https://upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png The Georgian Planet in her 1827 collection of poetry.
* "Uranus, the Magician" is a movement in Gustav Holst's orchestral suite *The Planets*, written between 1914 and 1916.
* Operation Uranus was the successful military operation in World War II by the Red Army to take back Stalingrad and marked the turning point in the land war against the Wehrmacht.
* The lines "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", are a reference to Herschel's discovery of Uranus.
* In English language popular culture, humor is often derived from the common pronunciation of Uranus' name, which resembles that of the phrase "your anus".