Uranus

This article is about the planet. For the Greek god, see Uranus (mythology). For other uses, see Uranus (disambiguation) and Uranian (disambiguation).

Uranus
Uranus in true colour,[a] as captured by Voyager 2. Its pale, muted appearance is due to a shroud of haze above its clouds
Discovery
Discovered byWilliam Herschel
Discovery date13 March 1781
Designations
Pronunciation/ˈjʊərənəs/ ⓘ[1] or /jʊˈreɪnəs/ ⓘ[2]
Named after
the Latin form Ūranus of the Greek god Οὐρανός Ouranos
AdjectivesUranian (/jʊˈreɪniən/)[3]
Symbol,
Orbital characteristics[4][b]
Epoch J2000
Aphelion20.0965 AU (3.00639 billion km)
Perihelion18.2861 AU (2.73556 billion km)
19.19126 AU (2.870972 billion km)
Eccentricity0.04717
  • 84.0205 yr
  • 30,688.5 d[5]
  • 42,718 Uranian solar days[6]
369.66 days[7]
Average orbital speed
6.80 km/s[7]
142.238600°
Inclination
74.006°
17–19 August 2050[9][10]
Argument of perihelion
96.998857°
Known satellites29
Physical characteristics
Mean radius
25,362±7 km[11][c]
Equatorial radius
25,559±4 km
4.007 Earths[11][c]
Polar radius
24,973±20 km
3.929 Earths[11][c]
Flattening0.0229±0.0008[d]
Circumference159,354.1 km[5]
8.1156×109 km2[5][c]
15.91 Earths
Volume6.833×1013 km3[7][c]
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[7][e]
Surface gravity
8.69 m/s2 (0.886 g0)[7][c]
Moment of inertia factor
0.23[13] (estimate)
21.3 km/s[7][c]
Synodic rotation period
−0.718649 d
−17h 14m 51s
(retrograde)
Sidereal rotation period
−0.718661 d
−17h 14m 52.310s ± 0.036s
(retrograde)[14]
Equatorial rotation velocity
2.59 km/s
82.23° (to orbit, retrograde).[7] 97.77°(prograde, right-hand rule)
North pole right ascension
17h 9m 15s
257.311°[11][15]
North pole declination
−15.175°[11][15]
Albedo0.300 (Bond)[16]
0.488 (geom.)[17]
Surface temp. min mean max
1 bar level[18] 76 K
(−197.2 °C)
0.1 bar
(tropopause)[19]		 47 K 53 K 57 K
5.38[20] to 6.03[20]
−7.2[21]
Angular diameter
3.3″ to 4.1″[7]
Atmosphere[19][22][23][f]
Scale height
27.7 km[7]
Composition by volumeBelow 1.3 bar (130 kPa):
Icy volatiles:

Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a supercritical phase of matter, which astronomy calls "ice" or volatiles. The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature (49 K (−224 °C; −371 °F)) of all the Solar System's planets. It has a marked axial tilt of 82.23° with a retrograde rotation period of 17 hours and 14 minutes. This means that in an 84-Earth-year orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness.

Uranus has the third-largest diameter and fourth-largest mass among the Solar System's planets. Based on current models, inside its volatile mantle layer is a rocky core, and surrounding it is a thick hydrogen and helium atmosphere. Trace amounts of hydrocarbons (thought to be produced via hydrolysis) and carbon monoxide along with carbon dioxide (thought to have originated from comets) have been detected in the upper atmosphere. There are many unexplained climate phenomena in Uranus's atmosphere, such as its peak wind speed of 900 km/h (560 mph),[24] variations in its polar cap, and its erratic cloud formation. The planet also has very low internal heat compared to other giant planets, the cause of which remains unclear.

Like the other giant planets, Uranus has a ring system, a magnetosphere, and many natural satellites. The extremely dark ring system reflects only about 2% of the incoming light. Uranus's 29 natural satellites include 19 known regular moons, of which 14 are small inner moons. Further out are the larger five major moons of the planet: Miranda, Ariel, Umbriel, Titania, and Oberon. Orbiting at a much greater distance from Uranus are the ten known irregular moons. The planet's magnetosphere is highly asymmetric and has many charged particles, which may be the cause of the darkening of its rings and moons.

Uranus is visible to the naked eye, but it is very dim and was not classified as a planet until 1781, when it was first observed by William Herschel. About seven decades after its discovery, consensus was reached that the planet be named after the Greek god Uranus (Ouranos), one of the Greek primordial deities. As of 2025, it has been visited only once when in 1986 the Voyager 2 probe flew by the planet.[25] Though nowadays it can be resolved and observed by telescopes, there is much desire to revisit the planet, as shown by Planetary Science Decadal Survey's decision to make the proposed Uranus Orbiter and Probe mission a top priority in the 2023–2032 survey, and the CNSA's proposal to fly by the planet with a subprobe of Tianwen-4.[26]


Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).

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  2. ^ Cite error: The named reference OED was invoked but never defined (see the help page).
  3. ^ "Uranian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. ^ Cite error: The named reference VSOP87 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference nasafact was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference CSeligman was invoked but never defined (see the help page).
  7. ^ a b c d e f g h i Cite error: The named reference fact was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Souami_Souchay_2012 was invoked but never defined (see the help page).
  9. ^ Jean Meeus, Astronomical Algorithms (Richmond, Virginia: Willmann-Bell, 1998) p271. Bretagnon's complete VSOP87 model. It gives the 17th @ 18.283075301au. http://vo.imcce.fr/webservices/miriade/?forms Archived 7 September 2021 at the Wayback Machine IMCCE Observatoire de Paris / CNRS Calculated for a series of dates, five or ten days apart, in August 2050, using an interpolation formula from Astronomical Algorithms. Perihelion came very early on the 17th. INPOP planetary theory
  10. ^ "HORIZONS Planet-center Batch call for August 2050 Perihelion". ssd.jpl.nasa.gov (Perihelion for Uranus planet-center (799) occurs on 2050-Aug-19 at 18.28307512au during a rdot flip from negative to positive). NASA/JPL. Archived from the original on 7 September 2021. Retrieved 7 September 2021.
  11. ^ a b c d e f Cite error: The named reference Seidelmann Archinal A'hearn et al. 2007 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Jacobson Campbell et al. 1992 was invoked but never defined (see the help page).
  13. ^ de Pater, Imke; Lissauer, Jack J. (2015). Planetary Sciences (2nd updated ed.). New York: Cambridge University Press. p. 250. ISBN 978-0521853712. Archived from the original on 26 November 2016. Retrieved 17 August 2016.
  14. ^ Cite error: The named reference Lamy2025 was invoked but never defined (see the help page).
  15. ^ a b Archinal, B. A.; Acton, C. H.; A'Hearn, M. F.; Conrad, A.; Consolmagno, G. J.; Duxbury, T.; Hestroffer, D.; Hilton, J. L.; Kirk, R. L.; Klioner, S. A.; McCarthy, D.; Meech, K.; Oberst, J.; Ping, J.; Seidelmann, P. K. (2018). "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015". Celestial Mechanics and Dynamical Astronomy. 130 (3): 22. Bibcode:2018CeMDA.130...22A. doi:10.1007/s10569-017-9805-5. ISSN 0923-2958.
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  19. ^ a b Cite error: The named reference Lunine 1993 was invoked but never defined (see the help page).
  20. ^ a b Cite error: The named reference Mallama_and_Hilton was invoked but never defined (see the help page).
  21. ^ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on 24 July 2023. Retrieved 29 May 2023.
  22. ^ Cite error: The named reference Lindal Lyons et al. 1987 was invoked but never defined (see the help page).
  23. ^ Cite error: The named reference Conrath Gautier et al. 1987 was invoked but never defined (see the help page).
  24. ^ Cite error: The named reference Sromovsky & Fry 2005 was invoked but never defined (see the help page).
  25. ^ "Exploration | Uranus". NASA Solar System Exploration. 10 November 2017. Archived from the original on 7 August 2020. Retrieved 8 February 2020. Jan. 24, 1986: NASA's Voyager 2 made the first - and so far the only - visit to Uranus.
  26. ^ Jones, Andrew (21 December 2023). "China's plans for outer Solar System exploration". The Planetary Society. Archived from the original on 31 December 2023. Retrieved 24 January 2024.
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