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Uranus

March 13, 2023

This article is about the planet. For the Greek god, see Uranus (mythology). For other uses, see Uranus (disambiguation). and Uranian (disambiguation). "Seventh planet" redirects here. For other systems of numbering planets, see Planet § History.

Uranus is the seventh planet from the Sun. It is named after Greek sky deity Uranus (Caelus), who in Greek mythology is the father of Cronus (Saturn), a grandfather of Zeus (Jupiter) and great-grandfather of Ares (Mars). Uranus has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. The planet is similar in composition to Neptune, and both have bulk chemical compositions which differ from those of the other two giant planets, Jupiter and Saturn (the gas giants). For this reason, scientists often distinguish Uranus and Neptune as "ice giants".

Uranus ()
Photograph of Uranus in true colour
(by Voyager 2 in 1986)
Discovery
Discovered byWilliam Herschel
Discovery date13 March 1781
Designations
Pronunciation/ˈjʊərənəs/ (listen)[1] or /jʊˈreɪnəs/ (listen)[2]
Named after
the Latin form Ūranus of the Greek god Οὐρανός Ouranos
AdjectivesUranian (/jʊˈreɪniən/)[3]
Orbital characteristics[10][a]
Epoch J2000
Aphelion20.0965 AU (3006.39 Gm)
Perihelion18.2861 AU (2735.56 Gm)
19.19126 AU (2870.972 Gm)
Eccentricity0.04717
369.66 days[6]
6.80 km/s[6]
142.238600°
Inclination
74.006°
17–19 August 2050[8][9]
96.998857°
Known satellites27
Physical characteristics
Mean radius
25,362±7 km[11][b]
Equatorial radius
25,559±4 km
4.007 Earths[11][b]
Polar radius
24,973±20 km
3.929 Earths[11][b]
Flattening0.0229±0.0008[c]
Circumference159,354.1 km[4]
8.1156×109 km2[4][b]
15.91 Earths
Volume6.833×1013 km3[6][b]
63.086 Earths
Mass(8.6810±0.0013)×1025 kg
14.536 Earths[12]
GM=5,793,939±13 km3/s2
Mean density
1.27 g/cm3[6][d]
8.69 m/s2[6][b]
0.886 g
0.23[13] (estimate)
21.3 km/s[6][b]
−0.71832 d
−17 h 14 m 23 s
(retrograde)[5]
−0.71833 d
−17 h 14 min 24 s
(retrograde)[11]
Equatorial rotation velocity
2.59 km/s
9,320 km/h
97.77° (to orbit)[6]
North pole right ascension
17h 9m 15s
257.311°[11]
North pole declination
−15.175°[11]
Albedo0.300 (Bond)[14]
0.488 (geom.)[15]
Surface temp. min mean max
1 bar level[16] 76 K
(−197.2 °C)
0.1 bar
(tropopause)[17]		 47 K 53 K 57 K
5.38[18] to 6.03[18]
3.3″ to 4.1″[6]
Atmosphere[17][19][20][e]
27.7 km[6]
Composition by volumeBelow 1.3 bar (130 kPa):
Icy volatiles:

As with gas giants, ice giants lack a well-defined solid surface. Uranus's atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons.[17] It has the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 kelvins (−224 °C; −371 °F). It has a complex, layered cloud structure; water is thought to make up the lowest clouds and methane the uppermost layer.[17] The planet's interior is mainly composed of ices and rock.[16]

Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration because its axis of rotation is tilted sideways, nearly into the plane of its solar orbit. Therefore, its north and south poles lie where most other planets have their equators.[21] In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, without the cloud bands or storms associated with the other giant planets.[21] No other spacecraft has yet visited the planet.[22] Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach 250 metres per second (900 km/h; 560 mph).[23]

History

 
Position of Uranus (marked with a cross) on the date of its discovery, the March 13th, 1781

Like the classical planets, Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit.[24] Sir William Herschel first observed Uranus on 13 March 1781, leading to its discovery as a planet, expanding the known boundaries of the Solar System for the first time in history and making Uranus the first planet classified as such with the aid of a telescope.

Discovery

Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star. Possibly the earliest known observation was by Hipparchos, who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy's Almagest.[25] The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri. The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769,[26] including on four consecutive nights.

Sir William Herschel observed Uranus on 13 March 1781 from the garden of his house at 19 New King Street in Bath, Somerset, England (now the Herschel Museum of Astronomy),[27] and initially reported it (on 26 April 1781) as a comet.[28] With a homemade 6.2-inch reflecting telescope, Herschel "engaged in a series of observations on the parallax of the fixed stars."[29][30]

Herschel recorded in his journal: "In the quartile near ζ Tauri ... either [a] Nebulous star or perhaps a comet."[31] On 17 March he noted: "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place."[32] When he presented his discovery to the Royal Society, he continued to assert that he had found a comet, but also implicitly compared it to a planet:[29]

The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed.[29]

Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this flummoxed reply from him on 23 April 1781: "I don't know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it."[33]

Although Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to compute the orbit of the new object.[34] Its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschel's discovery as "a moving star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn".[35] Bode concluded that its near-circular orbit was more like a planet's than a comet's.[36]

The object was soon universally accepted as a new planet. By 1783, Herschel acknowledged this to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honour of pointing out to them in March 1781, is a Primary Planet of our Solar System."[37] In recognition of his achievement, King George III gave Herschel an annual stipend of £200 (equivalent to £26,000 in 2021)[38] on condition that he move to Windsor so that the Royal Family could look through his telescopes.[39]

Name

The name of Uranus references the ancient Greek deity of the sky Uranus (Ancient Greek: Οὐρανός), known as Caelus in Roman mythology, the father of Cronus (Saturn) and grandfather of Zeus (Jupiter), which was rendered as Uranus in Latin (IPA: [ˈuːranʊs]).[2] It is the only one of the eight planets whose English name derives from a figure of Greek mythology. The adjectival form of Uranus is "Uranian".[40] The pronunciation of the name Uranus preferred among astronomers is /ˈjʊərənəs/ YOOR-ə-nəs,[1] with stress on the first syllable as in Latin Uranus, in contrast to /jʊˈreɪnəs/ yoo-RAY-nəs, with stress on the second syllable and a long a, though both are considered acceptable.[f]

Consensus on the name was not reached until almost 70 years after the planet's discovery. During the original discussions following discovery, Maskelyne asked Herschel to "do the astronomical world the faver [sic] to give a name to your planet, which is entirely your own, [and] which we are so much obliged to you for the discovery of".[42] In response to Maskelyne's request, Herschel decided to name the object Georgium Sidus (George's Star), or the "Georgian Planet" in honour of his new patron, King George III.[43] He explained this decision in a letter to Joseph Banks:[37]

In the fabulous ages of ancient times the appellations of Mercury, Venus, Mars, Jupiter and Saturn were given to the Planets, as being the names of their principal heroes and divinities. In the present more philosophical era it would hardly be allowable to have recourse to the same method and call it Juno, Pallas, Apollo or Minerva, for a name to our new heavenly body. The first consideration of any particular event, or remarkable incident, seems to be its chronology: if in any future age it should be asked, when this last-found Planet was discovered? It would be a very satisfactory answer to say, 'In the reign of King George the Third'.

Herschel's proposed name was not popular outside of Britain and Hanover, and alternatives were soon proposed. Astronomer Jérôme Lalande proposed that it be named Herschel in honour of its discoverer.[44] Swedish astronomer Erik Prosperin proposed the name Neptune, which was supported by other astronomers who liked the idea to commemorate the victories of the British Royal Naval fleet in the course of the American Revolutionary War by calling the new planet even Neptune George III or Neptune Great Britain.[34]

In a March 1782 treatise, Bode proposed Uranus, the Latinised version of the Greek god of the sky, Ouranos.[45] Bode argued that the name should follow the mythology so as not to stand out as different from the other planets, and that Uranus was an appropriate name as the father of the first generation of the Titans.[45] He also noted that elegance of the name in that just as Saturn was the father of Jupiter, the new planet should be named after the father of Saturn.[39][45][46][47] Bode was however apparently unaware that Uranus was only the Latinised form of the titular deity, and his Roman equivalent was Caelus. In 1789, Bode's Royal Academy colleague Martin Klaproth named his newly discovered element uranium in support of Bode's choice.[48] Ultimately, Bode's suggestion became the most widely used, and became universal in 1850 when HM Nautical Almanac Office, the final holdout, switched from using Georgium Sidus to Uranus.[46]

Uranus has two astronomical symbols. The first to be proposed,  ,[g] was proposed by Johann Gottfried Köhler at Bode's request in 1782.[49] Köhler suggested that the new planet be given the symbol for platinum, which had been described scientifically only 30 years before. As there was no alchemical symbol for platinum, he suggested ⛢ or ⛢, a combination of the planetary-metal symbols ☉ (gold) and ♂ (iron), as platinum (or 'white gold') is found mixed with iron. Bode thought that an upright orientation, ⛢, fit better with the symbols for the other planets while remaining distinct.[49] This symbol predominates in modern astronomical use in the rare cases that symbols are used at all.[50][51] The second symbol,  ,[h] was suggested by Lalande in 1784. In a letter to Herschel, Lalande described it as "un globe surmonté par la première lettre de votre nom" ("a globe surmounted by the first letter of your surname").[44] The second symbol is nearly universal in astrology.

Uranus is called by a variety of names in other languages. In Chinese, Japanese, Korean, and Vietnamese, its name is literally translated as the "sky king star" (天王星).[52][53][54][55] In Thai, its official name is Dao Yurenat (ดาวยูเรนัส), as in English. Its other name in Thai is Dao Maruettayu (ดาวมฤตยู, Star of Mṛtyu), after the Sanskrit word for 'death', Mrtyu (मृत्यु). In Mongolian, its name is Tengeriin Van (Тэнгэрийн ван), translated as 'King of the Sky', reflecting its namesake god's role as the ruler of the heavens. In Hawaiian, its name is Heleʻekala, the Hawaiian rendering of the name 'Herschel'.[56] In Māori, its name is Whērangi.[57][58]

Orbit and rotation

Uranus orbits the Sun once every 84 years. In 2033, the planet will have made its third complete orbit around the Sun since being discovered in 1781. The planet has returned to the point of its discovery northeast of Zeta Tauri twice since then, on 25 March 1865 and 29 March 1949. Uranus will return to this location again on 3 April 2033. Its average distance from the Sun is roughly 20 AU (3 billion km; 2 billion mi). The difference between its minimum and maximum distance from the Sun is 1.8 AU, larger than that of any other planet, though not as large as that of dwarf planet Pluto.[59] The intensity of sunlight varies inversely with the square of distance, and so on Uranus (at about 20 times the distance from the Sun compared to Earth) it is about 1/400 the intensity of light on Earth.[60]

The orbital elements of Uranus were first calculated in 1783 by Pierre-Simon Laplace.[61] With time, discrepancies began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On 23 September 1846, Johann Gottfried Galle located a new planet, later named Neptune, at nearly the position predicted by Le Verrier.[62]

The rotational period of the interior of Uranus is 17 hours, 14 minutes. As on all the giant planets, its upper atmosphere experiences strong winds in the direction of rotation. At some latitudes, such as about 60 degrees south, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.[63]

Axial tilt

 
Simulated Earth view of Uranus from 1986 to 2030, from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028.

The Uranian axis of rotation is approximately parallel with the plane of the Solar System, with an axial tilt of 97.77° (as defined by prograde rotation). This gives it seasonal changes completely unlike those of the other planets. Near the solstice, one pole faces the Sun continuously and the other faces away, with only a narrow strip around the equator experiencing a rapid day–night cycle, with the Sun low over the horizon. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.[64] Near the time of the equinoxes, the Sun faces the equator of Uranus giving a period of day–night cycles similar to those seen on most of the other planets.

One result of this axis orientation is that, averaged over the Uranian year, the near-polar regions of Uranus receive a greater energy input from the Sun than its equatorial regions. Nevertheless, Uranus is hotter at its equator than at its poles. The underlying mechanism that causes this is unknown. The reason for Uranus's unusual axial tilt is also not known with certainty, but the usual speculation is that during the formation of the Solar System, an Earth-sized protoplanet collided with Uranus, causing the skewed orientation.[65] Research by Jacob Kegerreis of Durham University suggests that the tilt resulted from a rock larger than the Earth crashing into the planet 3 to 4 billion years ago.[66] Uranus's south pole was pointed almost directly at the Sun at the time of Voyager 2's flyby in 1986. The labelling of this pole as "south" uses the definition currently endorsed by the International Astronomical Union, namely that the north pole of a planet or satellite is the pole that points above the invariable plane of the Solar System, regardless of the direction the planet is spinning.[67][68] A different convention is sometimes used, in which a body's north and south poles are defined according to the right-hand rule in relation to the direction of rotation.[69]

List of solstices and equinoxes[70]
Northern hemisphere Year Southern hemisphere
Winter solstice 1902, 1986, 2069 Summer solstice
Vernal equinox 1923, 2007, 2092 Autumnal equinox
Summer solstice 1944, 2030 Winter solstice
Autumnal equinox 1965, 2050 Vernal equinox

Visibility

 
Movement of Uranus in front of the stars of Aries in 2022

The mean apparent magnitude of Uranus is 5.68 with a standard deviation of 0.17, while the extremes are 5.38 and 6.03.[18] This range of brightness is near the limit of naked eye visibility. Much of the variability is dependent upon the planetary latitudes being illuminated from the Sun and viewed from the Earth.[71] Its angular diameter is between 3.4 and 3.7 arcseconds, compared with 16 to 20 arcseconds for Saturn and 32 to 45 arcseconds for Jupiter.[72] At opposition, Uranus is visible to the naked eye in dark skies, and becomes an easy target even in urban conditions with binoculars.[6] In larger amateur telescopes with an objective diameter of between 15 and 23 cm, Uranus appears as a pale cyan disk with distinct limb darkening. With a large telescope of 25 cm or wider, cloud patterns, as well as some of the larger satellites, such as Titania and Oberon, may be visible.[73]

Physical characteristics

Internal structure

 
Size comparison of Earth and Uranus
 
Diagram of the interior of Uranus

Uranus's mass is roughly 14.5 times that of Earth, making it the least massive of the giant planets. Its diameter is slightly larger than Neptune's at roughly four times that of Earth. A resulting density of 1.27 g/cm3 makes Uranus the second least dense planet, after Saturn.[11][12] This value indicates that it is made primarily of various ices, such as water, ammonia, and methane.[16] The total mass of ice in Uranus's interior is not precisely known, because different figures emerge depending on the model chosen; it must be between 9.3 and 13.5 Earth masses.[16][74] Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses.[16] The remainder of the non-ice mass (0.5 to 3.7 Earth masses) is accounted for by rocky material.[16]

The standard model of Uranus's structure is that it consists of three layers: a rocky (silicate/iron–nickel) core in the centre, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope.[16][75] The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20% of Uranus'; the mantle comprises its bulk, with around 13.4 Earth masses, and the upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and extending for the last 20% of Uranus's radius.[16][75] Uranus's core density is around 9 g/cm3, with a pressure in the centre of 8 million bars (800 GPa) and a temperature of about 5000 K.[74][75] The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles.[16][75] This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.[76]

The extreme pressure and temperature deep within Uranus may break up the methane molecules, with the carbon atoms condensing into crystals of diamond that rain down through the mantle like hailstones.[77][78] This phenomenon is similar to diamond rains that are theorised by scientists to exist on Jupiter, Saturn, and Neptune.[79][80] Very-high-pressure experiments at the Lawrence Livermore National Laboratory suggest that the base of the mantle may comprise an ocean of metallic liquid carbon, perhaps with floating solid 'diamond-bergs'.[81][82][83]

The bulk compositions of Uranus and Neptune are different from those of Jupiter and Saturn, with ice dominating over gases, hence justifying their separate classification as ice giants. There may be a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions move freely within the oxygen lattice.[84]

Although the model considered above is reasonably standard, it is not unique; other models also satisfy observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in the ice mantle, the total mass of ices in the interior will be lower, and, correspondingly, the total mass of rocks and hydrogen will be higher. Presently available data does not allow a scientific determination of which model is correct.[74] The fluid interior structure of Uranus means that it has no solid surface. The gaseous atmosphere gradually transitions into the internal liquid layers.[16] For the sake of convenience, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1 bar (100 kPa) is conditionally designated as a "surface". It has equatorial and polar radii of 25,559 ± 4 km (15,881.6 ± 2.5 mi) and 24,973 ± 20 km (15,518 ± 12 mi), respectively.[11] This surface is used throughout this article as a zero point for altitudes.

Internal heat

Uranus's internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux.[23][85] Why Uranus's internal temperature is so low is still not understood. Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun,[23] but Uranus radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06±0.08 times the solar energy absorbed in its atmosphere.[17][86] Uranus's heat flux is only 0.042±0.047 W/m2, which is lower than the internal heat flux of Earth of about 0.075 W/m2.[86] The lowest temperature recorded in Uranus's tropopause is 49 K (−224.2 °C; −371.5 °F), making Uranus the coldest planet in the Solar System.[17][86]

One of the hypotheses for this discrepancy suggests that when Uranus was hit by a supermassive impactor, which caused it to expel most of its primordial heat, it was left with a depleted core temperature.[87] This impact hypothesis is also used in some attempts to explain the planet's axial tilt. Another hypothesis is that some form of barrier exists in Uranus's upper layers that prevents the core's heat from reaching the surface.[16] For example, convection may take place in a set of compositionally different layers, which may inhibit the upward heat transport;[17][86] perhaps double diffusive convection is a limiting factor.[16]

In a 2021 study the ice giants' interior conditions were mimicked by compressing water containing minerals like olivine and ferropericlase, thus showing that large amounts of magnesium could be dissolved in the liquid interiors of Uranus and Neptune. If Uranus has more of this magnesium than Neptune it could form a thermal insulation layer, thus potentially explaining the planet's low temperature.[88]

Atmosphere

Main article: Atmosphere of Uranus
 
Uranus's atmosphere taken during the Outer Planet Atmosphere Legacy (OPAL) program.[89]

Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope that is accessible to remote sensing is called its atmosphere.[17] Remote-sensing capability extends down to roughly 300 km below the 1 bar (100 kPa) level, with a corresponding pressure around 100 bar (10 MPa) and temperature of 320 K (47 °C; 116 °F).[90] The tenuous thermosphere extends over two planetary radii from the nominal surface, which is defined to lie at a pressure of 1 bar.[91] The Uranian atmosphere can be divided into three layers: the troposphere, between altitudes of −300 and 50 km (−186 and 31 mi) and pressures from 100 to 0.1 bar (10 MPa to 10 kPa); the stratosphere, spanning altitudes between 50 and 4,000 km (31 and 2,485 mi) and pressures of between 0.1 and 10−10 bar (10 kPa to 10 µPa); and the thermosphere extending from 4,000 km to as high as 50,000 km from the surface.[17] There is no mesosphere.

Composition

The composition of Uranus's atmosphere is different from its bulk, consisting mainly of molecular hydrogen and helium.[17] The helium molar fraction, i.e. the number of helium atoms per molecule of gas, is 0.15±0.03[20] in the upper troposphere, which corresponds to a mass fraction 0.26±0.05.[17][86] This value is close to the protosolar helium mass fraction of 0.275±0.01,[92] indicating that helium has not settled in its centre as it has in the gas giants.[17] The third-most-abundant component of Uranus's atmosphere is methane (CH4).[17] Methane has prominent absorption bands in the visible and near-infrared (IR), making Uranus aquamarine or cyan in colour.[17] Methane molecules account for 2.3% of the atmosphere by molar fraction below the methane cloud deck at the pressure level of 1.3 bar (130 kPa); this represents about 20 to 30 times the carbon abundance found in the Sun.[17][19][93] The mixing ratio[i] is much lower in the upper atmosphere due to its extremely low temperature, which lowers the saturation level and causes excess methane to freeze out.[94] The abundances of less volatile compounds such as ammonia, water, and hydrogen sulfide in the deep atmosphere are poorly known. They are probably also higher than solar values.[17][95] Along with methane, trace amounts of various hydrocarbons are found in the stratosphere of Uranus, which are thought to be produced from methane by photolysis induced by the solar ultraviolet (UV) radiation.[96] They include ethane (C2H6), acetylene (C2H2), methylacetylene (CH3C2H), and diacetylene (C2HC2H).[94][97][98] Spectroscopy has also uncovered traces of water vapour, carbon monoxide and carbon dioxide in the upper atmosphere, which can only originate from an external source such as infalling dust and comets.[97][98][99]

Troposphere

The troposphere is the lowest and densest part of the atmosphere and is characterised by a decrease in temperature with altitude.[17] The temperature falls from about 320 K (47 °C; 116 °F) at the base of the nominal troposphere at −300 km to 53 K (−220 °C; −364 °F) at 50 km.[90][93] The temperatures in the coldest upper region of the troposphere (the tropopause) actually vary in the range between 49 and 57 K (−224 and −216 °C; −371 and −357 °F) depending on planetary latitude.[17][85] The tropopause region is responsible for the vast majority of Uranus's thermal far infrared emissions, thus determining its effective temperature of 59.1 ± 0.3 K (−214.1 ± 0.3 °C; −353.3 ± 0.5 °F).[85][86]

The troposphere is thought to have a highly complex cloud structure; water clouds are hypothesised to lie in the pressure range of 50 to 100 bar (5 to 10 MPa), ammonium hydrosulfide clouds in the range of 20 to 40 bar (2 to 4 MPa), ammonia or hydrogen sulfide clouds at between 3 and 10 bar (0.3 and 1 MPa) and finally directly detected thin methane clouds at 1 to 2 bar (0.1 to 0.2 MPa).[17][19][90][100] The troposphere is a dynamic part of the atmosphere, exhibiting strong winds, bright clouds and seasonal changes.[23]

Upper atmosphere

 
Aurorae on Uranus taken by the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.[101]

The middle layer of the Uranian atmosphere is the stratosphere, where temperature generally increases with altitude from 53 K (−220 °C; −364 °F) in the tropopause to between 800 and 850 K (527 and 577 °C; 980 and 1,070 °F) at the base of the thermosphere.[91] The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons,[102] which form in this part of the atmosphere as a result of methane photolysis.[96] Heat is also conducted from the hot thermosphere.[102] The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding to a pressure range of 1000 to 10 Pa and temperatures of between 75 and 170 K (−198 and −103 °C; −325 and −154 °F).[94][97]

The most abundant hydrocarbons are methane, acetylene and ethane with mixing ratios of around 10−7 relative to hydrogen. The mixing ratio of carbon monoxide is similar at these altitudes.[94][97][99] Heavier hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower.[97] The abundance ratio of water is around 7×10−9.[98] Ethane and acetylene tend to condense in the colder lower part of stratosphere and tropopause (below 10 mBar level) forming haze layers,[96] which may be partly responsible for the bland appearance of Uranus. The concentration of hydrocarbons in the Uranian stratosphere above the haze is significantly lower than in the stratospheres of the other giant planets.[94][103]

The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature around 800 to 850 K.[17][103] The heat sources necessary to sustain such a high level are not understood, as neither the solar UV nor the auroral activity can provide the necessary energy to maintain these temperatures. The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0.1 mBar pressure level may contribute too.[91][103] In addition to molecular hydrogen, the thermosphere-corona contains many free hydrogen atoms. Their small mass and high temperatures explain why the corona extends as far as 50,000 km (31,000 mi), or two Uranian radii, from its surface.[91][103] This extended corona is a unique feature of Uranus.[103] Its effects include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings.[91] The Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus.[93] Observations show that the ionosphere occupies altitudes from 2,000 to 10,000 km (1,200 to 6,200 mi).[93] The Uranian ionosphere is denser than that of either Saturn or Neptune, which may arise from the low concentration of hydrocarbons in the stratosphere.[103][104] The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity.[105] Auroral activity is insignificant as compared to Jupiter and Saturn.[103][106]

Magnetosphere

 
The magnetic field of Uranus
(animated; 25 March 2020)

Before the arrival of Voyager 2, no measurements of the Uranian magnetosphere had been taken, so its nature remained a mystery. Before 1986, scientists had expected the magnetic field of Uranus to be in line with the solar wind, because it would then align with Uranus's poles that lie in the ecliptic.[107]

Voyager's observations revealed that Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation.[107][108] In fact the magnetic dipole is shifted from Uranus's centre towards the south rotational pole by as much as one third of the planetary radius.[107] This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1 gauss (10 µT), whereas in the northern hemisphere it can be as high as 1.1 gauss (110 µT).[107] The average field at the surface is 0.23 gauss (23 µT).[107]

Studies of Voyager 2 data in 2017 suggest that this asymmetry causes Uranus's magnetosphere to connect with the solar wind once a Uranian day, opening the planet to the Sun's particles.[109] In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator.[108] The dipole moment of Uranus is 50 times that of Earth.[107][108] Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants.[108] One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean.[76][110] Another possible explanation for the magnetosphere's alignment is that there are oceans of liquid diamond in Uranus's interior that would deter the magnetic field.[82]

Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a bow shock at about 23 Uranian radii ahead of it, a magnetopause at 18 Uranian radii, a fully developed magnetotail, and radiation belts.[107][108][111] Overall, the structure of Uranus's magnetosphere is different from Jupiter's and more similar to Saturn's.[107][108] Uranus's magnetotail trails behind it into space for millions of kilometres and is twisted by its sideways rotation into a long corkscrew.[107][112]

Uranus's magnetosphere contains charged particles: mainly protons and electrons, with a small amount of H2+ ions.[108][111] Many of these particles probably derive from the thermosphere.[111] The ion and electron energies can be as high as 4 and 1.2 megaelectronvolts, respectively.[111] The density of low-energy (below 1 kiloelectronvolt) ions in the inner magnetosphere is about 2 cm−3.[113] The particle population is strongly affected by the Uranian moons, which sweep through the magnetosphere, leaving noticeable gaps.[111] The particle flux is high enough to cause darkening or space weathering of their surfaces on an astronomically rapid timescale of 100,000 years.[111] This may be the cause of the uniformly dark colouration of the Uranian satellites and rings.[114] Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles.[103] Unlike Jupiter's, Uranus's aurorae seem to be insignificant for the energy balance of the planetary thermosphere.[106] In March 2020, NASA astronomers reported the detection of a large atmospheric magnetic bubble, also known as a plasmoid, released into outer space from the planet Uranus, after reevaluating old data recorded by the Voyager 2 space probe during a flyby of the planet in 1986.[115][116]

Climate

Main article: Climate of Uranus

At ultraviolet and visible wavelengths, Uranus's atmosphere is bland in comparison to the other giant planets, even to Neptune, which it otherwise closely resembles.[23] When Voyager 2 flew by Uranus in 1986, it observed a total of ten cloud features across the entire planet.[21][117] One proposed explanation for this dearth of features is that Uranus's internal heat is markedly lower than that of the other giant planets, as stated previously Uranus is the coldest planet in the Solar System.[17][86]

Banded structure, winds and clouds

 
The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.

In 1986, Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions: a bright polar cap and dark equatorial bands.[21] Their boundary is located at about −45° of latitude. A narrow band straddling the latitudinal range from −45 to −50° is the brightest large feature on its visible surface.[21][118] It is called a southern "collar". The cap and collar are thought to be a dense region of methane clouds located within the pressure range of 1.3 to 2 bar (see above).[119] Besides the large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to the north from the collar.[21] In all other respects Uranus looked like a dynamically dead planet in 1986.

Voyager 2 arrived during the height of Uranus's southern summer and could not observe the northern hemisphere. At the beginning of the 21st century, when the northern polar region came into view, the Hubble Space Telescope (HST) and Keck telescope initially observed neither a collar nor a polar cap in the northern hemisphere.[118] So Uranus appeared to be asymmetric: bright near the south pole and uniformly dark in the region north of the southern collar.[118] In 2007, when Uranus passed its equinox, the southern collar almost disappeared, and a faint northern collar emerged near 45° of latitude.[120]

In the 1990s, the number of the observed bright cloud features grew considerably partly because new high-resolution imaging techniques became available.[23] Most were found in the northern hemisphere as it started to become visible.[23] An early explanation—that bright clouds are easier to identify in its dark part, whereas in the southern hemisphere the bright collar masks them – was shown to be incorrect.[121][122] Nevertheless, there are differences between the clouds of each hemisphere. The northern clouds are smaller, sharper and brighter.[122] They appear to lie at a higher altitude.[122] The lifetime of clouds spans several orders of magnitude. Some small clouds live for hours; at least one southern cloud may have persisted since the Voyager 2 flyby.[23][117] Recent observation also discovered that cloud features on Uranus have a lot in common with those on Neptune.[23] For example, the dark spots common on Neptune had never been observed on Uranus before 2006, when the first such feature dubbed Uranus Dark Spot was imaged.[123] The speculation is that Uranus is becoming more Neptune-like during its equinoctial season.[124]

The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of Uranus.[23] At the equator winds are retrograde, which means that they blow in the reverse direction to the planetary rotation. Their speeds are from −360 to −180 km/h (−220 to −110 mph).[23][118] Wind speeds increase with the distance from the equator, reaching zero values near ±20° latitude, where the troposphere's temperature minimum is located.[23][85] Closer to the poles, the winds shift to a prograde direction, flowing with Uranus's rotation. Wind speeds continue to increase reaching maxima at ±60° latitude before falling to zero at the poles.[23] Wind speeds at −40° latitude range from 540 to 720 km/h (340 to 450 mph). Because the collar obscures all clouds below that parallel, speeds between it and the southern pole are impossible to measure.[23] In contrast, in the northern hemisphere maximum speeds as high as 860 km/h (540 mph) are observed near +50° latitude.[23][118][125]

Seasonal variation

 
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).

For a short period from March to May 2004, large clouds appeared in the Uranian atmosphere, giving it a Neptune-like appearance.[122][126] Observations included record-breaking wind speeds of 820 km/h (510 mph) and a persistent thunderstorm referred to as "Fourth of July fireworks".[117] On 23 August 2006, researchers at the Space Science Institute (Boulder, Colorado) and the University of Wisconsin observed a dark spot on Uranus's surface, giving scientists more insight into Uranus atmospheric activity.[123] Why this sudden upsurge in activity occurred is not fully known, but it appears that Uranus's extreme axial tilt results in extreme seasonal variations in its weather.[127][124] Determining the nature of this seasonal variation is difficult because good data on Uranus's atmosphere has existed for less than 84 years, or one full Uranian year. Photometry over the course of half a Uranian year (beginning in the 1950s) has shown regular variation in the brightness in two spectral bands, with maxima occurring at the solstices and minima occurring at the equinoxes.[128] A similar periodic variation, with maxima at the solstices, has been noted in microwave measurements of the deep troposphere begun in the 1960s.[129] Stratospheric temperature measurements beginning in the 1970s also showed maximum values near the 1986 solstice.[102] The majority of this variability is thought to occur owing to changes in the viewing geometry.[121]

There are some indications that physical seasonal changes are happening in Uranus. Although Uranus is known to have a bright south polar region, the north pole is fairly dim, which is incompatible with the model of the seasonal change outlined above.[124] During its previous northern solstice in 1944, Uranus displayed elevated levels of brightness, which suggests that the north pole was not always so dim.[128] This information implies that the visible pole brightens some time before the solstice and darkens after the equinox.[124] Detailed analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the solstices, which also indicates a change in the meridional albedo patterns.[124] In the 1990s, as Uranus moved away from its solstice, Hubble and ground-based telescopes revealed that the south polar cap darkened noticeably (except the southern collar, which remained bright),[119] whereas the northern hemisphere demonstrated increasing activity,[117] such as cloud formations and stronger winds, bolstering expectations that it should brighten soon.[122] This indeed happened in 2007 when it passed an equinox: a faint northern polar collar arose, and the southern collar became nearly invisible, although the zonal wind profile remained slightly asymmetric, with northern winds being somewhat slower than southern.[120]

The mechanism of these physical changes is still not clear.[124] Near the summer and winter solstices, Uranus's hemispheres lie alternately either in full glare of the Sun's rays or facing deep space. The brightening of the sunlit hemisphere is thought to result from the local thickening of the methane clouds and haze layers located in the troposphere.[119] The bright collar at −45° latitude is also connected with methane clouds.[119] Other changes in the southern polar region can be explained by changes in the lower cloud layers.[119] The variation of the microwave emission from Uranus is probably caused by changes in the deep tropospheric circulation, because thick polar clouds and haze may inhibit convection.[130] Now that the spring and autumn equinoxes are arriving on Uranus, the dynamics are changing and convection can occur again.[117][130]

Formation

Main article: Formation and evolution of the Solar System
For details of the evolution of Uranus's orbit, see Nice model.

It is argued that the differences between the ice giants and the gas giants arise from their formation history.[131][132][133] The Solar System is hypothesised to have formed from a rotating disk of gas and dust known as the presolar nebula. Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, and 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 on to the nebula's leftover gas.[131][132][134] 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.[135] The ice giants, with only a few Earth masses of nebular gas, never reached that critical point.[131][132][136] 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 (the Nice model).[131]

Moons

Main article: Moons of Uranus
See also: Timeline of discovery of Solar System planets and their moons
 
Major moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos (collage of Voyager 2 photographs)

Uranus has 27 known natural satellites.[136] The names of these satellites are chosen from characters in the works of Shakespeare and Alexander Pope.[75][137] The five main satellites are Miranda, Ariel, Umbriel, Titania, and Oberon.[75] The Uranian satellite system is the least massive among those of the giant planets; the combined mass of the five major satellites would be less than half that of Triton (largest moon of Neptune) alone.[12] The largest of Uranus's satellites, Titania, has a radius of only 788.9 km (490.2 mi), or less than half that of the Moon, but slightly more than Rhea, the second-largest satellite of Saturn, making Titania the eighth-largest moon in the Solar System. Uranus's satellites have relatively low albedos; ranging from 0.20 for Umbriel to 0.35 for Ariel (in green light).[21] They are ice–rock conglomerates composed of roughly 50% ice and 50% rock. The ice may include ammonia and carbon dioxide.[114][138]

Among the Uranian satellites, Ariel appears to have the youngest surface, with the fewest impact craters, and Umbriel the oldest.[21][114] Miranda has fault canyons 20 km (12 mi) deep, terraced layers, and a chaotic variation in surface ages and features.[21] Miranda's past geologic activity is thought to have been driven by tidal heating at a time when its orbit was more eccentric than currently, probably as a result of a former 3:1 orbital resonance with Umbriel.[139] Extensional processes associated with upwelling diapirs are the likely origin of Miranda's 'racetrack'-like coronae.[140][141] Ariel is thought to have once been held in a 4:1 resonance with Titania.[142]

Uranus has at least one horseshoe orbiter occupying the Sun–Uranus L3 Lagrangian point—a gravitationally unstable region at 180° in its orbit, 83982 Crantor.[143][144] Crantor moves inside Uranus's co-orbital region on a complex, temporary horseshoe orbit. 2010 EU65 is also a promising Uranus horseshoe librator candidate.[144]

Rings

Main article: Rings of Uranus
 
Uranus's aurorae against its equatorial rings, imaged by the Hubble telescope. Unlike the aurorae of Earth and Jupiter, those of Uranus are not in line with its poles, due to its lopsided magnetic field.

The Uranian rings are composed of extremely dark particles, which vary in size from micrometres to a fraction of a metre.[21] 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.[114][145]

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.[146][147] 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.[148] Later they detected four additional rings.[148] The rings were directly imaged when Voyager 2 passed Uranus in 1986.[21] Voyager 2 also discovered two additional faint rings, bringing the total number to eleven.[21]

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.[149] 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.[150][151] 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.[150][152] In contrast, Uranus's inner rings appear grey.[150]

Exploration

Main article: Exploration of Uranus
 
Crescent Uranus as imaged by Voyager 2 while en route to Neptune

In 1986, NASA's Voyager 2 interplanetary probe encountered Uranus. This flyby remains the only investigation of Uranus carried out from a short distance and no other visits are planned. Voyager 1 was unable to visit Uranus because investigation of Saturn's moon Titan was considered a priority. This trajectory took Voyager 1 out of the plane of the ecliptic, ending its planetary science mission.[153]: 118  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,[93] 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.[21][114][154] It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.[107]

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.[155] It would have taken about twenty years to get to the Uranian system after departing Saturn.[155] 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.[156] A Uranus entry probe could use Pioneer Venus Multiprobe heritage and descend to 1–5 atmospheres.[156] The ESA evaluated a "medium-class" mission called Uranus Pathfinder.[157] A New Frontiers Uranus Orbiter has been evaluated and recommended in the study, The Case for a Uranus Orbiter.[158] 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.[159] For more concepts see proposed Uranus missions.

In April, 2022, the next Planetary Science Decadal Survey placed its highest priority for the next "flagship" project on a full package mission (orbiter and probe) to Uranus, with a projected launch window starting in 2031. The "dearth" of ice giant science was key to its prioritization. Another key issue was that such a mission would use extant technology, and not require development of other instruments and systems to be successful.[160]

In culture

See also

Notes

  1. ^ These are the mean elements from VSOP87, together with derived quantities.
  2. ^ a b c d e f g Refers to the level of 1 bar atmospheric pressure.
  3. ^ Calculated using data from Seidelmann, 2007.[11]
  4. ^ Based on the volume within the level of 1 bar atmospheric pressure.
  5. ^ Calculation of He, H2 and CH4 molar fractions is based on a 2.3% mixing ratio of methane to hydrogen and the 15/85 He/H2 proportions measured at the tropopause.
  6. ^ Because, in the English-speaking world, the latter sounds like "your anus", the former pronunciation also saves embarrassment: as Pamela Gay, an astronomer at Southern Illinois University Edwardsville, noted on her podcast, to avoid "being made fun of by any small schoolchildren ... when in doubt, don't emphasise anything and just say /ˈjʊərənəs/. And then run, quickly."[41]
  7. ^ Cf.   (not supported by all fonts)
  8. ^ Cf.   (not supported by all fonts)
  9. ^ Mixing ratio is defined as the number of molecules of a compound per a molecule of hydrogen.

References

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    Bereits in der am 12ten März 1782 bei der hiesigen naturforschenden Gesellschaft vorgelesenen Abhandlung, habe ich den Namen des Vaters vom Saturn, nemlich Uranos, oder wie er mit der lateinischen Endung gewöhnlicher ist, Uranus vorgeschlagen, und habe seit dem das Vergnügen gehabt, daß verschiedene Astronomen und Mathematiker in ihren Schriften oder in Briefen an mich, diese Benennung aufgenommen oder gebilligt. Meines Erachtens muß man bei dieser Wahl die Mythologie befolgen, aus welcher die uralten Namen der übrigen Planeten entlehnen worden; denn in der Reihe der bisher bekannten, würde der von einer merkwürdigen Person oder Begebenheit der neuern Zeit wahrgenommene Name eines Planeten sehr auffallen. Diodor von Cicilien erzahlt die Geschichte der Atlanten, eines uralten Volks, welches eine der fruchtbarsten Gegenden in Africa bewohnte, und die Meeresküsten seines Landes als das Vaterland der Götter ansah. Uranus war ihr, erster König, Stifter ihres gesitteter Lebens und Erfinder vieler nützlichen Künste. Zugleich wird er auch als ein fleißiger und geschickter Himmelsforscher des Alterthums beschrieben... Noch mehr: Uranus war der Vater des Saturns und des Atlas, so wie der erstere der Vater des Jupiters.

    [Translated]:

    Already in the pre-read at the local Natural History Society on 12th March 1782 treatise, I have the father's name from Saturn, namely Uranos, or as it is usually with the Latin suffix, proposed Uranus, and have since had the pleasure that various astronomers and mathematicians, cited in their writings or letters to me approving this designation. In my view, it is necessary to follow the mythology in this election, which had been borrowed from the ancient name of the other planets; because in the series of previously known, perceived by a strange person or event of modern times name of a planet would very noticeable. Diodorus of Cilicia tells the story of Atlas, an ancient people that inhabited one of the most fertile areas in Africa, and looked at the sea shores of his country as the homeland of the gods. Uranus was her first king, founder of their civilized life and inventor of many useful arts. At the same time he is also described as a diligent and skilful astronomers of antiquity ... even more: Uranus was the father of Saturn and the Atlas, as the former is the father of Jupiter.
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Further reading

  • Tereza Pultarova (1 October 2021). "Stinky 'mushball' hailstones on Uranus may explain an atmospheric anomaly there (and on Neptune, too)". Space.com.
  • Miner, Ellis D. (1998). Uranus: The Planet, Rings and Satellites. New York: John Wiley and Sons. ISBN 978-0-471-97398-0.
  • Gore, Rick (August 1986). "Uranus: Voyager Visits a Dark Planet". National Geographic. Vol. 170, no. 2. pp. 178–194. ISSN 0027-9358. OCLC 643483454.
  • Alexander, Arthur Francis O'Donel (1965). The Planet Uranus: A History of Observation, Theory and Discovery. New York, American Elsevier Pub. Co.
  • Bode, Johann Elert (1784). "Von dem neu entdeckten Planeten". Von dem Neu Entdeckten Planeten. bey dem Verfasser [etc.] Bibcode:1784vdne.book.....B. doi:10.3931/e-rara-1454.

External links

March 13, 2023
uranus, this, article, about, planet, greek, mythology, other, uses, disambiguation, uranian, disambiguation, seventh, planet, redirects, here, other, systems, numbering, planets, planet, history, seventh, planet, from, named, after, greek, deity, caelus, gree. This article is about the planet For the Greek god see Uranus mythology For other uses see Uranus disambiguation and Uranian disambiguation Seventh planet redirects here For other systems of numbering planets see Planet History Uranus is the seventh planet from the Sun It is named after Greek sky deity Uranus Caelus who in Greek mythology is the father of Cronus Saturn a grandfather of Zeus Jupiter and great grandfather of Ares Mars Uranus has the third largest planetary radius and fourth largest planetary mass in the Solar System The planet is similar in composition to Neptune and both have bulk chemical compositions which differ from those of the other two giant planets Jupiter and Saturn the gas giants For this reason scientists often distinguish Uranus and Neptune as ice giants Uranus Photograph of Uranus in true colour by Voyager 2 in 1986 DiscoveryDiscovered byWilliam HerschelDiscovery date13 March 1781DesignationsPronunciation ˈ jʊer e n e s listen 1 or j ʊ ˈ r eɪ n e s listen 2 Named afterthe Latin form uranus of the Greek god Oὐranos OuranosAdjectivesUranian j ʊ ˈ r eɪ n i e n 3 Orbital characteristics 10 a Epoch J2000Aphelion20 0965 AU 3006 39 Gm Perihelion18 2861 AU 2735 56 Gm Semi major axis19 19126 AU 2870 972 Gm Eccentricity0 04717Orbital period sidereal 84 0205 yr 30 688 5 d 4 42 718 Uranian solar days 5 Orbital period synodic 369 66 days 6 Average orbital speed6 80 km s 6 Mean anomaly142 238600 Inclination0 773 to ecliptic6 48 to Sun s equator0 99 to invariable plane 7 Longitude of ascending node74 006 Time of perihelion17 19 August 2050 8 9 Argument of perihelion96 998857 Known satellites27Physical characteristicsMean radius25 362 7 km 11 b Equatorial radius25 559 4 km 4 007 Earths 11 b Polar radius24 973 20 km 3 929 Earths 11 b Flattening0 0229 0 0008 c Circumference159 354 1 km 4 Surface area8 1156 109 km2 4 b 15 91 EarthsVolume6 833 1013 km3 6 b 63 086 EarthsMass 8 6810 0 0013 1025 kg 14 536 Earths 12 GM 5 793 939 13 km3 s2Mean density1 27 g cm3 6 d Surface gravity8 69 m s2 6 b 0 886 gMoment of inertia factor0 23 13 estimate Escape velocity21 3 km s 6 b Synodic rotation period 0 71832 d 17 h 14 m 23 s retrograde 5 Sidereal rotation period 0 71833 d 17 h 14 min 24 s retrograde 11 Equatorial rotation velocity2 59 km s 9 320 km hAxial tilt97 77 to orbit 6 North pole right ascension17h 9m 15s 257 311 11 North pole declination 15 175 11 Albedo0 300 Bond 14 0 488 geom 15 Surface temp min mean max1 bar level 16 76 K 197 2 C 0 1 bar tropopause 17 47 K 53 K 57 KApparent magnitude5 38 18 to 6 03 18 Angular diameter3 3 to 4 1 6 Atmosphere 17 19 20 e Scale height27 7 km 6 Composition by volumeBelow 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 ammoniawater iceammonium hydrosulfidemethane hydrateAs with gas giants ice giants lack a well defined solid surface Uranus s atmosphere is similar to Jupiter s and Saturn s in its primary composition of hydrogen and helium but it contains more ices such as water ammonia and methane along with traces of other hydrocarbons 17 It has the coldest planetary atmosphere in the Solar System with a minimum temperature of 49 kelvins 224 C 371 F It has a complex layered cloud structure water is thought to make up the lowest clouds and methane the uppermost layer 17 The planet s interior is mainly composed of ices and rock 16 Like the other giant planets Uranus has a ring system a magnetosphere and numerous moons The Uranian system has a unique configuration because its axis of rotation is tilted sideways nearly into the plane of its solar orbit Therefore its north and south poles lie where most other planets have their equators 21 In 1986 images from Voyager 2 showed Uranus as an almost featureless planet in visible light without the cloud bands or storms associated with the other giant planets 21 No other spacecraft has yet visited the planet 22 Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007 Wind speeds can reach 250 metres per second 900 km h 560 mph 23 Contents 1 History 1 1 Discovery 1 2 Name 2 Orbit and rotation 2 1 Axial tilt 2 2 Visibility 3 Physical characteristics 3 1 Internal structure 3 1 1 Internal heat 3 2 Atmosphere 3 2 1 Composition 3 2 2 Troposphere 3 2 3 Upper atmosphere 3 3 Magnetosphere 4 Climate 4 1 Banded structure winds and clouds 4 2 Seasonal variation 5 Formation 6 Moons 7 Rings 8 Exploration 9 In culture 10 See also 11 Notes 12 References 13 Further reading 14 External linksHistory Position of Uranus marked with a cross on the date of its discovery the March 13th 1781 Like the classical planets Uranus is visible to the naked eye but it was never recognised as a planet by ancient observers because of its dimness and slow orbit 24 Sir William Herschel first observed Uranus on 13 March 1781 leading to its discovery as a planet expanding the known boundaries of the Solar System for the first time in history and making Uranus the first planet classified as such with the aid of a telescope Discovery Uranus had been observed on many occasions before its recognition as a planet but it was generally mistaken for a star Possibly the earliest known observation was by Hipparchos who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy s Almagest 25 The earliest definite sighting was in 1690 when John Flamsteed observed it at least six times cataloguing it as 34 Tauri The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769 26 including on four consecutive nights Sir William Herschel observed Uranus on 13 March 1781 from the garden of his house at 19 New King Street in Bath Somerset England now the Herschel Museum of Astronomy 27 and initially reported it on 26 April 1781 as a comet 28 With a homemade 6 2 inch reflecting telescope Herschel engaged in a series of observations on the parallax of the fixed stars 29 30 Herschel recorded in his journal In the quartile near z Tauri either a Nebulous star or perhaps a comet 31 On 17 March he noted I looked for the Comet or Nebulous Star and found that it is a Comet for it has changed its place 32 When he presented his discovery to the Royal Society he continued to assert that he had found a comet but also implicitly compared it to a planet 29 The power I had on when I first saw the comet was 227 From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers as planets are therefore I now put the powers at 460 and 932 and found that the diameter of the comet increased in proportion to the power as it ought to be on the supposition of its not being a fixed star while the diameters of the stars to which I compared it were not increased in the same ratio Moreover the comet being magnified much beyond what its light would admit of appeared hazy and ill defined with these great powers while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain The sequel has shown that my surmises were well founded this proving to be the Comet we have lately observed 29 Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this flummoxed reply from him on 23 April 1781 I don t know what to call it It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis I have not yet seen any coma or tail to it 33 Although Herschel continued to describe his new object as a comet other astronomers had already begun to suspect otherwise Finnish Swedish astronomer Anders Johan Lexell working in Russia was the first to compute the orbit of the new object 34 Its nearly circular orbit led him to a conclusion that it was a planet rather than a comet Berlin astronomer Johann Elert Bode described Herschel s discovery as a moving star that can be deemed a hitherto unknown planet like object circulating beyond the orbit of Saturn 35 Bode concluded that its near circular orbit was more like a planet s than a comet s 36 The object was soon universally accepted as a new planet By 1783 Herschel acknowledged this to Royal Society president Joseph Banks By the observation of the most eminent Astronomers in Europe it appears that the new star which I had the honour of pointing out to them in March 1781 is a Primary Planet of our Solar System 37 In recognition of his achievement King George III gave Herschel an annual stipend of 200 equivalent to 26 000 in 2021 38 on condition that he move to Windsor so that the Royal Family could look through his telescopes 39 Name The name of Uranus references the ancient Greek deity of the sky Uranus Ancient Greek Oὐranos known as Caelus in Roman mythology the father of Cronus Saturn and grandfather of Zeus Jupiter which was rendered as Uranus in Latin IPA ˈuːranʊs 2 It is the only one of the eight planets whose English name derives from a figure of Greek mythology The adjectival form of Uranus is Uranian 40 The pronunciation of the name Uranus preferred among astronomers is ˈ jʊer e n e s YOOR e nes 1 with stress on the first syllable as in Latin Uranus in contrast to j ʊ ˈ r eɪ n e s yoo RAY nes with stress on the second syllable and a long a though both are considered acceptable f Consensus on the name was not reached until almost 70 years after the planet s discovery During the original discussions following discovery Maskelyne asked Herschel to do the astronomical world the faver sic to give a name to your planet which is entirely your own and which we are so much obliged to you for the discovery of 42 In response to Maskelyne s request Herschel decided to name the object Georgium Sidus George s Star or the Georgian Planet in honour of his new patron King George III 43 He explained this decision in a letter to Joseph Banks 37 In the fabulous ages of ancient times the appellations of Mercury Venus Mars Jupiter and Saturn were given to the Planets as being the names of their principal heroes and divinities In the present more philosophical era it would hardly be allowable to have recourse to the same method and call it Juno Pallas Apollo or Minerva for a name to our new heavenly body The first consideration of any particular event or remarkable incident seems to be its chronology if in any future age it should be asked when this last found Planet was discovered It would be a very satisfactory answer to say In the reign of King George the Third Herschel s proposed name was not popular outside of Britain and Hanover and alternatives were soon proposed Astronomer Jerome Lalande proposed that it be named Herschel in honour of its discoverer 44 Swedish astronomer Erik Prosperin proposed the name Neptune which was supported by other astronomers who liked the idea to commemorate the victories of the British Royal Naval fleet in the course of the American Revolutionary War by calling the new planet even Neptune George III or Neptune Great Britain 34 In a March 1782 treatise Bode proposed Uranus the Latinised version of the Greek god of the sky Ouranos 45 Bode argued that the name should follow the mythology so as not to stand out as different from the other planets and that Uranus was an appropriate name as the father of the first generation of the Titans 45 He also noted that elegance of the name in that just as Saturn was the father of Jupiter the new planet should be named after the father of Saturn 39 45 46 47 Bode was however apparently unaware that Uranus was only the Latinised form of the titular deity and his Roman equivalent was Caelus In 1789 Bode s Royal Academy colleague Martin Klaproth named his newly discovered element uranium in support of Bode s choice 48 Ultimately Bode s suggestion became the most widely used and became universal in 1850 when HM Nautical Almanac Office the final holdout switched from using Georgium Sidus to Uranus 46 Uranus has two astronomical symbols The first to be proposed g was proposed by Johann Gottfried Kohler at Bode s request in 1782 49 Kohler suggested that the new planet be given the symbol for platinum which had been described scientifically only 30 years before As there was no alchemical symbol for platinum he suggested or a combination of the planetary metal symbols gold and iron as platinum or white gold is found mixed with iron Bode thought that an upright orientation fit better with the symbols for the other planets while remaining distinct 49 This symbol predominates in modern astronomical use in the rare cases that symbols are used at all 50 51 The second symbol h was suggested by Lalande in 1784 In a letter to Herschel Lalande described it as un globe surmonte par la premiere lettre de votre nom a globe surmounted by the first letter of your surname 44 The second symbol is nearly universal in astrology Uranus is called by a variety of names in other languages In Chinese Japanese Korean and Vietnamese its name is literally translated as the sky king star 天王星 52 53 54 55 In Thai its official name is Dao Yurenat dawyuerns as in English Its other name in Thai is Dao Maruettayu dawmvtyu Star of Mṛtyu after the Sanskrit word for death Mrtyu म त य In Mongolian its name is Tengeriin Van Tengerijn van translated as King of the Sky reflecting its namesake god s role as the ruler of the heavens In Hawaiian its name is Heleʻekala the Hawaiian rendering of the name Herschel 56 In Maori its name is Wherangi 57 58 Orbit and rotationUranus orbits the Sun once every 84 years In 2033 the planet will have made its third complete orbit around the Sun since being discovered in 1781 The planet has returned to the point of its discovery northeast of Zeta Tauri twice since then on 25 March 1865 and 29 March 1949 Uranus will return to this location again on 3 April 2033 Its average distance from the Sun is roughly 20 AU 3 billion km 2 billion mi The difference between its minimum and maximum distance from the Sun is 1 8 AU larger than that of any other planet though not as large as that of dwarf planet Pluto 59 The intensity of sunlight varies inversely with the square of distance and so on Uranus at about 20 times the distance from the Sun compared to Earth it is about 1 400 the intensity of light on Earth 60 The orbital elements of Uranus were first calculated in 1783 by Pierre Simon Laplace 61 With time discrepancies began to appear between the predicted and observed orbits and in 1841 John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet In 1845 Urbain Le Verrier began his own independent research into Uranus s orbit On 23 September 1846 Johann Gottfried Galle located a new planet later named Neptune at nearly the position predicted by Le Verrier 62 The rotational period of the interior of Uranus is 17 hours 14 minutes As on all the giant planets its upper atmosphere experiences strong winds in the direction of rotation At some latitudes such as about 60 degrees south visible features of the atmosphere move much faster making a full rotation in as little as 14 hours 63 Axial tilt Simulated Earth view of Uranus from 1986 to 2030 from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028 The Uranian axis of rotation is approximately parallel with the plane of the Solar System with an axial tilt of 97 77 as defined by prograde rotation This gives it seasonal changes completely unlike those of the other planets Near the solstice one pole faces the Sun continuously and the other faces away with only a narrow strip around the equator experiencing a rapid day night cycle with the Sun low over the horizon At the other side of Uranus s orbit the orientation of the poles towards the Sun is reversed Each pole gets around 42 years of continuous sunlight followed by 42 years of darkness 64 Near the time of the equinoxes the Sun faces the equator of Uranus giving a period of day night cycles similar to those seen on most of the other planets One result of this axis orientation is that averaged over the Uranian year the near polar regions of Uranus receive a greater energy input from the Sun than its equatorial regions Nevertheless Uranus is hotter at its equator than at its poles The underlying mechanism that causes this is unknown The reason for Uranus s unusual axial tilt is also not known with certainty but the usual speculation is that during the formation of the Solar System an Earth sized protoplanet collided with Uranus causing the skewed orientation 65 Research by Jacob Kegerreis of Durham University suggests that the tilt resulted from a rock larger than the Earth crashing into the planet 3 to 4 billion years ago 66 Uranus s south pole was pointed almost directly at the Sun at the time of Voyager 2 s flyby in 1986 The labelling of this pole as south uses the definition currently endorsed by the International Astronomical Union namely that the north pole of a planet or satellite is the pole that points above the invariable plane of the Solar System regardless of the direction the planet is spinning 67 68 A different convention is sometimes used in which a body s north and south poles are defined according to the right hand rule in relation to the direction of rotation 69 List of solstices and equinoxes 70 Northern hemisphere Year Southern hemisphereWinter solstice 1902 1986 2069 Summer solsticeVernal equinox 1923 2007 2092 Autumnal equinoxSummer solstice 1944 2030 Winter solsticeAutumnal equinox 1965 2050 Vernal equinoxVisibility Movement of Uranus in front of the stars of Aries in 2022 The mean apparent magnitude of Uranus is 5 68 with a standard deviation of 0 17 while the extremes are 5 38 and 6 03 18 This range of brightness is near the limit of naked eye visibility Much of the variability is dependent upon the planetary latitudes being illuminated from the Sun and viewed from the Earth 71 Its angular diameter is between 3 4 and 3 7 arcseconds compared with 16 to 20 arcseconds for Saturn and 32 to 45 arcseconds for Jupiter 72 At opposition Uranus is visible to the naked eye in dark skies and becomes an easy target even in urban conditions with binoculars 6 In larger amateur telescopes with an objective diameter of between 15 and 23 cm Uranus appears as a pale cyan disk with distinct limb darkening With a large telescope of 25 cm or wider cloud patterns as well as some of the larger satellites such as Titania and Oberon may be visible 73 Physical characteristicsInternal structure Size comparison of Earth and Uranus Diagram of the interior of Uranus Uranus s mass is roughly 14 5 times that of Earth making it the least massive of the giant planets Its diameter is slightly larger than Neptune s at roughly four times that of Earth A resulting density of 1 27 g cm3 makes Uranus the second least dense planet after Saturn 11 12 This value indicates that it is made primarily of various ices such as water ammonia and methane 16 The total mass of ice in Uranus s interior is not precisely known because different figures emerge depending on the model chosen it must be between 9 3 and 13 5 Earth masses 16 74 Hydrogen and helium constitute only a small part of the total with between 0 5 and 1 5 Earth masses 16 The remainder of the non ice mass 0 5 to 3 7 Earth masses is accounted for by rocky material 16 The standard model of Uranus s structure is that it consists of three layers a rocky silicate iron nickel core in the centre an icy mantle in the middle and an outer gaseous hydrogen helium envelope 16 75 The core is relatively small with a mass of only 0 55 Earth masses and a radius less than 20 of Uranus the mantle comprises its bulk with around 13 4 Earth masses and the upper atmosphere is relatively insubstantial weighing about 0 5 Earth masses and extending for the last 20 of Uranus s radius 16 75 Uranus s core density is around 9 g cm3 with a pressure in the centre of 8 million bars 800 GPa and a temperature of about 5000 K 74 75 The ice mantle is not in fact composed of ice in the conventional sense but of a hot and dense fluid consisting of water ammonia and other volatiles 16 75 This fluid which has a high electrical conductivity is sometimes called a water ammonia ocean 76 The extreme pressure and temperature deep within Uranus may break up the methane molecules with the carbon atoms condensing into crystals of diamond that rain down through the mantle like hailstones 77 78 This phenomenon is similar to diamond rains that are theorised by scientists to exist on Jupiter Saturn and Neptune 79 80 Very high pressure experiments at the Lawrence Livermore National Laboratory suggest that the base of the mantle may comprise an ocean of metallic liquid carbon perhaps with floating solid diamond bergs 81 82 83 The bulk compositions of Uranus and Neptune are different from those of Jupiter and Saturn with ice dominating over gases hence justifying their separate classification as ice giants There may be a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions and deeper down superionic water in which the oxygen crystallises but the hydrogen ions move freely within the oxygen lattice 84 Although the model considered above is reasonably standard it is not unique other models also satisfy observations For instance if substantial amounts of hydrogen and rocky material are mixed in the ice mantle the total mass of ices in the interior will be lower and correspondingly the total mass of rocks and hydrogen will be higher Presently available data does not allow a scientific determination of which model is correct 74 The fluid interior structure of Uranus means that it has no solid surface The gaseous atmosphere gradually transitions into the internal liquid layers 16 For the sake of convenience a revolving oblate spheroid set at the point at which atmospheric pressure equals 1 bar 100 kPa is conditionally designated as a surface It has equatorial and polar radii of 25 559 4 km 15 881 6 2 5 mi and 24 973 20 km 15 518 12 mi respectively 11 This surface is used throughout this article as a zero point for altitudes Internal heat Uranus s internal heat appears markedly lower than that of the other giant planets in astronomical terms it has a low thermal flux 23 85 Why Uranus s internal temperature is so low is still not understood Neptune which is Uranus s near twin in size and composition radiates 2 61 times as much energy into space as it receives from the Sun 23 but Uranus radiates hardly any excess heat at all The total power radiated by Uranus in the far infrared i e heat part of the spectrum is 1 06 0 08 times the solar energy absorbed in its atmosphere 17 86 Uranus s heat flux is only 0 042 0 047 W m2 which is lower than the internal heat flux of Earth of about 0 075 W m2 86 The lowest temperature recorded in Uranus s tropopause is 49 K 224 2 C 371 5 F making Uranus the coldest planet in the Solar System 17 86 One of the hypotheses for this discrepancy suggests that when Uranus was hit by a supermassive impactor which caused it to expel most of its primordial heat it was left with a depleted core temperature 87 This impact hypothesis is also used in some attempts to explain the planet s axial tilt Another hypothesis is that some form of barrier exists in Uranus s upper layers that prevents the core s heat from reaching the surface 16 For example convection may take place in a set of compositionally different layers which may inhibit the upward heat transport 17 86 perhaps double diffusive convection is a limiting factor 16 In a 2021 study the ice giants interior conditions were mimicked by compressing water containing minerals like olivine and ferropericlase thus showing that large amounts of magnesium could be dissolved in the liquid interiors of Uranus and Neptune If Uranus has more of this magnesium than Neptune it could form a thermal insulation layer thus potentially explaining the planet s low temperature 88 Atmosphere Main article Atmosphere of Uranus Uranus s atmosphere taken during the Outer Planet Atmosphere Legacy OPAL program 89 Although there is no well defined solid surface within Uranus s interior the outermost part of Uranus s gaseous envelope that is accessible to remote sensing is called its atmosphere 17 Remote sensing capability extends down to roughly 300 km below the 1 bar 100 kPa level with a corresponding pressure around 100 bar 10 MPa and temperature of 320 K 47 C 116 F 90 The tenuous thermosphere extends over two planetary radii from the nominal surface which is defined to lie at a pressure of 1 bar 91 The Uranian atmosphere can be divided into three layers the troposphere between altitudes of 300 and 50 km 186 and 31 mi and pressures from 100 to 0 1 bar 10 MPa to 10 kPa the stratosphere spanning altitudes between 50 and 4 000 km 31 and 2 485 mi and pressures of between 0 1 and 10 10 bar 10 kPa to 10 µPa and the thermosphere extending from 4 000 km to as high as 50 000 km from the surface 17 There is no mesosphere Composition The composition of Uranus s atmosphere is different from its bulk consisting mainly of molecular hydrogen and helium 17 The helium molar fraction i e the number of helium atoms per molecule of gas is 0 15 0 03 20 in the upper troposphere which corresponds to a mass fraction 0 26 0 05 17 86 This value is close to the protosolar helium mass fraction of 0 275 0 01 92 indicating that helium has not settled in its centre as it has in the gas giants 17 The third most abundant component of Uranus s atmosphere is methane CH4 17 Methane has prominent absorption bands in the visible and near infrared IR making Uranus aquamarine or cyan in colour 17 Methane molecules account for 2 3 of the atmosphere by molar fraction below the methane cloud deck at the pressure level of 1 3 bar 130 kPa this represents about 20 to 30 times the carbon abundance found in the Sun 17 19 93 The mixing ratio i is much lower in the upper atmosphere due to its extremely low temperature which lowers the saturation level and causes excess methane to freeze out 94 The abundances of less volatile compounds such as ammonia water and hydrogen sulfide in the deep atmosphere are poorly known They are probably also higher than solar values 17 95 Along with methane trace amounts of various hydrocarbons are found in the stratosphere of Uranus which are thought to be produced from methane by photolysis induced by the solar ultraviolet UV radiation 96 They include ethane C2H6 acetylene C2H2 methylacetylene CH3C2H and diacetylene C2HC2H 94 97 98 Spectroscopy has also uncovered traces of water vapour carbon monoxide and carbon dioxide in the upper atmosphere which can only originate from an external source such as infalling dust and comets 97 98 99 Troposphere The troposphere is the lowest and densest part of the atmosphere and is characterised by a decrease in temperature with altitude 17 The temperature falls from about 320 K 47 C 116 F at the base of the nominal troposphere at 300 km to 53 K 220 C 364 F at 50 km 90 93 The temperatures in the coldest upper region of the troposphere the tropopause actually vary in the range between 49 and 57 K 224 and 216 C 371 and 357 F depending on planetary latitude 17 85 The tropopause region is responsible for the vast majority of Uranus s thermal far infrared emissions thus determining its effective temperature of 59 1 0 3 K 214 1 0 3 C 353 3 0 5 F 85 86 The troposphere is thought to have a highly complex cloud structure water clouds are hypothesised to lie in the pressure range of 50 to 100 bar 5 to 10 MPa ammonium hydrosulfide clouds in the range of 20 to 40 bar 2 to 4 MPa ammonia or hydrogen sulfide clouds at between 3 and 10 bar 0 3 and 1 MPa and finally directly detected thin methane clouds at 1 to 2 bar 0 1 to 0 2 MPa 17 19 90 100 The troposphere is a dynamic part of the atmosphere exhibiting strong winds bright clouds and seasonal changes 23 Upper atmosphere Aurorae on Uranus taken by the Space Telescope Imaging Spectrograph STIS installed on Hubble 101 The middle layer of the Uranian atmosphere is the stratosphere where temperature generally increases with altitude from 53 K 220 C 364 F in the tropopause to between 800 and 850 K 527 and 577 C 980 and 1 070 F at the base of the thermosphere 91 The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons 102 which form in this part of the atmosphere as a result of methane photolysis 96 Heat is also conducted from the hot thermosphere 102 The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding to a pressure range of 1000 to 10 Pa and temperatures of between 75 and 170 K 198 and 103 C 325 and 154 F 94 97 The most abundant hydrocarbons are methane acetylene and ethane with mixing ratios of around 10 7 relative to hydrogen The mixing ratio of carbon monoxide is similar at these altitudes 94 97 99 Heavier hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower 97 The abundance ratio of water is around 7 10 9 98 Ethane and acetylene tend to condense in the colder lower part of stratosphere and tropopause below 10 mBar level forming haze layers 96 which may be partly responsible for the bland appearance of Uranus The concentration of hydrocarbons in the Uranian stratosphere above the haze is significantly lower than in the stratospheres of the other giant planets 94 103 The outermost layer of the Uranian atmosphere is the thermosphere and corona which has a uniform temperature around 800 to 850 K 17 103 The heat sources necessary to sustain such a high level are not understood as neither the solar UV nor the auroral activity can provide the necessary energy to maintain these temperatures The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0 1 mBar pressure level may contribute too 91 103 In addition to molecular hydrogen the thermosphere corona contains many free hydrogen atoms Their small mass and high temperatures explain why the corona extends as far as 50 000 km 31 000 mi or two Uranian radii from its surface 91 103 This extended corona is a unique feature of Uranus 103 Its effects include a drag on small particles orbiting Uranus causing a general depletion of dust in the Uranian rings 91 The Uranian thermosphere together with the upper part of the stratosphere corresponds to the ionosphere of Uranus 93 Observations show that the ionosphere occupies altitudes from 2 000 to 10 000 km 1 200 to 6 200 mi 93 The Uranian ionosphere is denser than that of either Saturn or Neptune which may arise from the low concentration of hydrocarbons in the stratosphere 103 104 The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity 105 Auroral activity is insignificant as compared to Jupiter and Saturn 103 106 Magnetosphere The magnetic field of Uranus animated 25 March 2020 Before the arrival of Voyager 2 no measurements of the Uranian magnetosphere had been taken so its nature remained a mystery Before 1986 scientists had expected the magnetic field of Uranus to be in line with the solar wind because it would then align with Uranus s poles that lie in the ecliptic 107 Voyager s observations revealed that Uranus s magnetic field is peculiar both because it does not originate from its geometric centre and because it is tilted at 59 from the axis of rotation 107 108 In fact the magnetic dipole is shifted from Uranus s centre towards the south rotational pole by as much as one third of the planetary radius 107 This unusual geometry results in a highly asymmetric magnetosphere where the magnetic field strength on the surface in the southern hemisphere can be as low as 0 1 gauss 10 µT whereas in the northern hemisphere it can be as high as 1 1 gauss 110 µT 107 The average field at the surface is 0 23 gauss 23 µT 107 Studies of Voyager 2 data in 2017 suggest that this asymmetry causes Uranus s magnetosphere to connect with the solar wind once a Uranian day opening the planet to the Sun s particles 109 In comparison the magnetic field of Earth is roughly as strong at either pole and its magnetic equator is roughly parallel with its geographical equator 108 The dipole moment of Uranus is 50 times that of Earth 107 108 Neptune has a similarly displaced and tilted magnetic field suggesting that this may be a common feature of ice giants 108 One hypothesis is that unlike the magnetic fields of the terrestrial and gas giants which are generated within their cores the ice giants magnetic fields are generated by motion at relatively shallow depths for instance in the water ammonia ocean 76 110 Another possible explanation for the magnetosphere s alignment is that there are oceans of liquid diamond in Uranus s interior that would deter the magnetic field 82 Despite its curious alignment in other respects the Uranian magnetosphere is like those of other planets it has a bow shock at about 23 Uranian radii ahead of it a magnetopause at 18 Uranian radii a fully developed magnetotail and radiation belts 107 108 111 Overall the structure of Uranus s magnetosphere is different from Jupiter s and more similar to Saturn s 107 108 Uranus s magnetotail trails behind it into space for millions of kilometres and is twisted by its sideways rotation into a long corkscrew 107 112 Uranus s magnetosphere contains charged particles mainly protons and electrons with a small amount of H2 ions 108 111 Many of these particles probably derive from the thermosphere 111 The ion and electron energies can be as high as 4 and 1 2 megaelectronvolts respectively 111 The density of low energy below 1 kiloelectronvolt ions in the inner magnetosphere is about 2 cm 3 113 The particle population is strongly affected by the Uranian moons which sweep through the magnetosphere leaving noticeable gaps 111 The particle flux is high enough to cause darkening or space weathering of their surfaces on an astronomically rapid timescale of 100 000 years 111 This may be the cause of the uniformly dark colouration of the Uranian satellites and rings 114 Uranus has relatively well developed aurorae which are seen as bright arcs around both magnetic poles 103 Unlike Jupiter s Uranus s aurorae seem to be insignificant for the energy balance of the planetary thermosphere 106 In March 2020 NASA astronomers reported the detection of a large atmospheric magnetic bubble also known as a plasmoid released into outer space from the planet Uranus after reevaluating old data recorded by the Voyager 2 space probe during a flyby of the planet in 1986 115 116 ClimateMain article Climate of Uranus At ultraviolet and visible wavelengths Uranus s atmosphere is bland in comparison to the other giant planets even to Neptune which it otherwise closely resembles 23 When Voyager 2 flew by Uranus in 1986 it observed a total of ten cloud features across the entire planet 21 117 One proposed explanation for this dearth of features is that Uranus s internal heat is markedly lower than that of the other giant planets as stated previously Uranus is the coldest planet in the Solar System 17 86 Banded structure winds and clouds The first dark spot observed on Uranus Image obtained by the HST ACS in 2006 In 1986 Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions a bright polar cap and dark equatorial bands 21 Their boundary is located at about 45 of latitude A narrow band straddling the latitudinal range from 45 to 50 is the brightest large feature on its visible surface 21 118 It is called a southern collar The cap and collar are thought to be a dense region of methane clouds located within the pressure range of 1 3 to 2 bar see above 119 Besides the large scale banded structure Voyager 2 observed ten small bright clouds most lying several degrees to the north from the collar 21 In all other respects Uranus looked like a dynamically dead planet in 1986 Voyager 2 arrived during the height of Uranus s southern summer and could not observe the northern hemisphere At the beginning of the 21st century when the northern polar region came into view the Hubble Space Telescope HST and Keck telescope initially observed neither a collar nor a polar cap in the northern hemisphere 118 So Uranus appeared to be asymmetric bright near the south pole and uniformly dark in the region north of the southern collar 118 In 2007 when Uranus passed its equinox the southern collar almost disappeared and a faint northern collar emerged near 45 of latitude 120 In the 1990s the number of the observed bright cloud features grew considerably partly because new high resolution imaging techniques became available 23 Most were found in the northern hemisphere as it started to become visible 23 An early explanation that bright clouds are easier to identify in its dark part whereas in the southern hemisphere the bright collar masks them was shown to be incorrect 121 122 Nevertheless there are differences between the clouds of each hemisphere The northern clouds are smaller sharper and brighter 122 They appear to lie at a higher altitude 122 The lifetime of clouds spans several orders of magnitude Some small clouds live for hours at least one southern cloud may have persisted since the Voyager 2 flyby 23 117 Recent observation also discovered that cloud features on Uranus have a lot in common with those on Neptune 23 For example the dark spots common on Neptune had never been observed on Uranus before 2006 when the first such feature dubbed Uranus Dark Spot was imaged 123 The speculation is that Uranus is becoming more Neptune like during its equinoctial season 124 The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of Uranus 23 At the equator winds are retrograde which means that they blow in the reverse direction to the planetary rotation Their speeds are from 360 to 180 km h 220 to 110 mph 23 118 Wind speeds increase with the distance from the equator reaching zero values near 20 latitude where the troposphere s temperature minimum is located 23 85 Closer to the poles the winds shift to a prograde direction flowing with Uranus s rotation Wind speeds continue to increase reaching maxima at 60 latitude before falling to zero at the poles 23 Wind speeds at 40 latitude range from 540 to 720 km h 340 to 450 mph Because the collar obscures all clouds below that parallel speeds between it and the southern pole are impossible to measure 23 In contrast in the northern hemisphere maximum speeds as high as 860 km h 540 mph are observed near 50 latitude 23 118 125 Seasonal variation Uranus in 2005 Rings southern collar and a bright cloud in the northern hemisphere are visible HST ACS image For a short period from March to May 2004 large clouds appeared in the Uranian atmosphere giving it a Neptune like appearance 122 126 Observations included record breaking wind speeds of 820 km h 510 mph and a persistent thunderstorm referred to as Fourth of July fireworks 117 On 23 August 2006 researchers at the Space Science Institute Boulder Colorado and the University of Wisconsin observed a dark spot on Uranus s surface giving scientists more insight into Uranus atmospheric activity 123 Why this sudden upsurge in activity occurred is not fully known but it appears that Uranus s extreme axial tilt results in extreme seasonal variations in its weather 127 124 Determining the nature of this seasonal variation is difficult because good data on Uranus s atmosphere has existed for less than 84 years or one full Uranian year Photometry over the course of half a Uranian year beginning in the 1950s has shown regular variation in the brightness in two spectral bands with maxima occurring at the solstices and minima occurring at the equinoxes 128 A similar periodic variation with maxima at the solstices has been noted in microwave measurements of the deep troposphere begun in the 1960s 129 Stratospheric temperature measurements beginning in the 1970s also showed maximum values near the 1986 solstice 102 The majority of this variability is thought to occur owing to changes in the viewing geometry 121 There are some indications that physical seasonal changes are happening in Uranus Although Uranus is known to have a bright south polar region the north pole is fairly dim which is incompatible with the model of the seasonal change outlined above 124 During its previous northern solstice in 1944 Uranus displayed elevated levels of brightness which suggests that the north pole was not always so dim 128 This information implies that the visible pole brightens some time before the solstice and darkens after the equinox 124 Detailed analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the solstices which also indicates a change in the meridional albedo patterns 124 In the 1990s as Uranus moved away from its solstice Hubble and ground based telescopes revealed that the south polar cap darkened noticeably except the southern collar which remained bright 119 whereas the northern hemisphere demonstrated increasing activity 117 such as cloud formations and stronger winds bolstering expectations that it should brighten soon 122 This indeed happened in 2007 when it passed an equinox a faint northern polar collar arose and the southern collar became nearly invisible although the zonal wind profile remained slightly asymmetric with northern winds being somewhat slower than southern 120 The mechanism of these physical changes is still not clear 124 Near the summer and winter solstices Uranus s hemispheres lie alternately either in full glare of the Sun s rays or facing deep space The brightening of the sunlit hemisphere is thought to result from the local thickening of the methane clouds and haze layers located in the troposphere 119 The bright collar at 45 latitude is also connected with methane clouds 119 Other changes in the southern polar region can be explained by changes in the lower cloud layers 119 The variation of the microwave emission from Uranus is probably caused by changes in the deep tropospheric circulation because thick polar clouds and haze may inhibit convection 130 Now that the spring and autumn equinoxes are arriving on Uranus the dynamics are changing and convection can occur again 117 130 FormationMain article Formation and evolution of the Solar System For details of the evolution of Uranus s orbit see Nice model It is argued that the differences between the ice giants and the gas giants arise from their formation history 131 132 133 The Solar System is hypothesised to have formed from a rotating disk of gas and dust known as the presolar nebula Much of the nebula s gas primarily hydrogen and helium formed the Sun and 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 on to the nebula s leftover gas 131 132 134 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 135 The ice giants with only a few Earth masses of nebular gas never reached that critical point 131 132 136 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 the Nice model 131 MoonsMain article Moons of Uranus See also Timeline of discovery of Solar System planets and their moons Major moons of Uranus in order of increasing distance left to right at their proper relative sizes and albedos collage of Voyager 2 photographs Uranus has 27 known natural satellites 136 The names of these satellites are chosen from characters in the works of Shakespeare and Alexander Pope 75 137 The five main satellites are Miranda Ariel Umbriel Titania and Oberon 75 The Uranian satellite system is the least massive among those of the giant planets the combined mass of the five major satellites would be less than half that of Triton largest moon of Neptune alone 12 The largest of Uranus s satellites Titania has a radius of only 788 9 km 490 2 mi or less than half that of the Moon but slightly more than Rhea the second largest satellite of Saturn making Titania the eighth largest moon in the Solar System Uranus s satellites have relatively low albedos ranging from 0 20 for Umbriel to 0 35 for Ariel in green light 21 They are ice rock conglomerates composed of roughly 50 ice and 50 rock The ice may include ammonia and carbon dioxide 114 138 Among the Uranian satellites Ariel appears to have the youngest surface with the fewest impact craters and Umbriel the oldest 21 114 Miranda has fault canyons 20 km 12 mi deep terraced layers and a chaotic variation in surface ages and features 21 Miranda s past geologic activity is thought to have been driven by tidal heating at a time when its orbit was more eccentric than currently probably as a result of a former 3 1 orbital resonance with Umbriel 139 Extensional processes associated with upwelling diapirs are the likely origin of Miranda s racetrack like coronae 140 141 Ariel is thought to have once been held in a 4 1 resonance with Titania 142 Uranus has at least one horseshoe orbiter occupying the Sun Uranus L3 Lagrangian point a gravitationally unstable region at 180 in its orbit 83982 Crantor 143 144 Crantor moves inside Uranus s co orbital region on a complex temporary horseshoe orbit 2010 EU65 is also a promising Uranus horseshoe librator candidate 144 RingsMain article Rings of Uranus Uranus s aurorae against its equatorial rings imaged by the Hubble telescope Unlike the aurorae of Earth and Jupiter those of Uranus are not in line with its poles due to its lopsided magnetic field The Uranian rings are composed of extremely dark particles which vary in size from micrometres to a fraction of a metre 21 Thirteen distinct rings are presently known the brightest being the e 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 114 145 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 146 147 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 148 Later they detected four additional rings 148 The rings were directly imaged when Voyager 2 passed Uranus in 1986 21 Voyager 2 also discovered two additional faint rings bringing the total number to eleven 21 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 13 149 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 150 151 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 150 152 In contrast Uranus s inner rings appear grey 150 ExplorationMain article Exploration of Uranus Crescent Uranus as imaged by Voyager 2 while en route to Neptune In 1986 NASA s Voyager 2 interplanetary probe encountered Uranus This flyby remains the only investigation of Uranus carried out from a short distance and no other visits are planned Voyager 1 was unable to visit Uranus because investigation of Saturn s moon Titan was considered a priority This trajectory took Voyager 1 out of the plane of the ecliptic ending its planetary science mission 153 118 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 93 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 21 114 154 It also studied the magnetic field its irregular structure its tilt and its unique corkscrew magnetotail caused by Uranus s sideways orientation 107 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 155 It would have taken about twenty years to get to the Uranian system after departing Saturn 155 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 156 A Uranus entry probe could use Pioneer Venus Multiprobe heritage and descend to 1 5 atmospheres 156 The ESA evaluated a medium class mission called Uranus Pathfinder 157 A New Frontiers Uranus Orbiter has been evaluated and recommended in the study The Case for a Uranus Orbiter 158 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 159 For more concepts see proposed Uranus missions In April 2022 the next Planetary Science Decadal Survey placed its highest priority for the next flagship project on a full package mission orbiter and probe to Uranus with a projected launch window starting in 2031 The dearth of ice giant science was key to its prioritization Another key issue was that such a mission would use extant technology and not require development of other instruments and systems to be successful 160 In cultureIn astrology the planet Uranus symbol 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 161 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 162 Lydia Sigourney included her poem 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 163 In English language popular culture humor is often derived from the common pronunciation of Uranus s name which resembles that of the phrase your anus 164 See also2011 QF99 and 2014 YX49 the only two known Uranus trojans Colonisation of Uranus Extraterrestrial diamonds thought to be abundant in Uranus Outline of Uranus Stats of planets in the Solar System Uranus in astrology Uranus in fictionNotes These are the mean elements from VSOP87 together with derived quantities a b c d e f g Refers to the level of 1 bar atmospheric pressure Calculated using data from Seidelmann 2007 11 Based on the volume within the level of 1 bar atmospheric pressure Calculation of He H2 and CH4 molar fractions is based on a 2 3 mixing ratio of methane to hydrogen and the 15 85 He H2 proportions measured at the tropopause Because in the English speaking world the latter sounds like your anus the former pronunciation also saves embarrassment as Pamela Gay an astronomer at Southern Illinois University Edwardsville noted on her podcast to avoid being made fun of by any small schoolchildren when in doubt don t emphasise anything and just say ˈjʊerenes And then run quickly 41 Cf not supported by all fonts Cf not supported by all fonts Mixing ratio is defined as the number of molecules of a compound per a molecule of hydrogen References a b Because the vowel a is short in both Greek and Latin the former pronunciation ˈjʊerenes is the expected one The BBC Pronunciation Unit notes that this pronunciation is the preferred usage of astronomers Olausson Lena Sangster Catherine 2006 The Oxford BBC Guide to Pronunciation Oxford England Oxford University Press p 404 ISBN 978 0 19 280710 6 a b Uranus Oxford English Dictionary Online ed Oxford University Press Subscription or participating institution membership required Uranian Oxford English Dictionary Online ed Oxford University Press Subscription or participating institution membership required a b c Munsell Kirk 14 May 2007 NASA Solar System Exploration Planets Uranus Facts amp Figures NASA Archived from the original on 14 December 2003 Retrieved 13 August 2007 a b Seligman Courtney Rotation Period and Day Length Archived from the original on 28 July 2011 Retrieved 13 August 2009 a b c d e f g h i j Williams Dr David R 31 January 2005 Uranus Fact Sheet NASA Archived from the original on 13 July 2017 Retrieved 10 August 2007 Souami D Souchay J July 2012 The solar system s invariable plane Astronomy amp Astrophysics 543 11 Bibcode 2012A amp A 543A 133S doi 10 1051 0004 6361 201219011 A133 Jean Meeus Astronomical Algorithms Richmond Virginia Willmann Bell 1998 p271 Bretagnon s complete VSOP87 model It gives 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Philadelphia Archived from the original on 28 August 2017 Retrieved 27 August 2017 Further readingTereza Pultarova 1 October 2021 Stinky mushball hailstones on Uranus may explain an atmospheric anomaly there and on Neptune too Space com Miner Ellis D 1998 Uranus The Planet Rings and Satellites New York John Wiley and Sons ISBN 978 0 471 97398 0 Gore Rick August 1986 Uranus Voyager Visits a Dark Planet National Geographic Vol 170 no 2 pp 178 194 ISSN 0027 9358 OCLC 643483454 Alexander Arthur Francis O Donel 1965 The Planet Uranus A History of Observation Theory and Discovery New York American Elsevier Pub Co Bode Johann Elert 1784 Von dem neu entdeckten Planeten Von dem Neu Entdeckten Planeten bey dem Verfasser etc Bibcode 1784vdne book B doi 10 3931 e rara 1454 External linksUranus at Wikipedia s sister projects Definitions from Wiktionary Media from Commons Quotations from Wikiquote Resources from Wikiversity Uranus at European Space Agency Uranus at NASA s Solar System Exploration site Uranus at Jet Propulsion Laboratory s planetary photojournal photos Voyager at Uranus Archived 4 January 2015 at the Wayback Machine photos Uranian system montage photo Gray Meghan Merrifield Michael 2010 Uranus Sixty Symbols Brady Haran for the University of Nottingham Interactive 3D gravity simulation of the Uranian system Archived 11 June 2020 at the Wayback Machine Portals Solar System Astronomy Stars Spaceflight Outer space Retrieved from https en wikipedia org w index php title Uranus amp oldid 1144178277, wikipedia, wiki, book, books, library,

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