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Uranus

seventh planet in the Solar System from the Sun
This article is about the planet. For the Greek god, see Uranus (mythology). For other uses, see Uranus (disambiguation).

Uranus is the seventh planet from the Sun in our Solar System. Like Neptune, it is an ice giant. It is the third largest planet in the solar system.

Uranus ⛢ (♅)
Photograph of Uranus in true colour (by Voyager 2 in 1986)
Discovery
Discovered byWilliam Herschel
Discovery date13 March 1781
Designations
Pronunciation/jʊˈreɪnəs/ (audio speaker iconlisten)[1][2] or /ˈjʊərənəs/ (audio speaker iconlisten)
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][20][21][e]
27.7 km[6]
Composition by volume(Below 1.3 bar)

Gases:

Ices:

The planet is made of ice, gases and liquid metal. Its atmosphere contains hydrogen, helium and methane. The temperature on Uranus is −197 °C (−322.6 °F; 76.1 K) near the top of its atmosphere. Its small solid core (about 55% the mass of Earth) is probably about 4,730 °C (8,540 °F; 5,000 K).

The planet is tilted on its axis so much that it is sideways.[22] Nobody knows why exactly it is. It has five big moons, many small ones, and a small system of 13 planetary rings.

The distance between Uranus and the Sun is about 2.8 billion km. Uranus completes its orbit around the Sun in 84 earth years. It completes a spin around its axis in 17 hours and 14 minutes. This means there are about 43,000 days in a year on Uranus.[23]

Uranus was discovered in 1781.[24] This planet can be seen with the naked eye under perfect conditions. John Flamsteed saw it decades before but thought it was a star (34 Tauri).

Near the solstice, one pole faces the Sun continuously and the other faces away. Only a narrow strip around the equator has a rapid day–night cycle, with the Sun low over the horizon. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.

Uranus is named after Uranus, the Greek mythology version of the Sumerian god Anu,[25] who was a god of the sky.

History

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Discovery

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Uranus has been seen many times through a telescope, and even sometimes without any, but people thought it was a star due to its slow orbit. 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),[26] and first said it was a comet (on 26 April 1781).[27] With a homemade 6.2-inch reflecting telescope, Herschel "engaged in a series of observations on the parallax of the fixed stars."[28][29]

Herschel wrote in his journal: "In the quartile near ζ Tauri... either [a] Nebulous star or perhaps a comet."[30] 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."[31] 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:[28]

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.[28]

Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this 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."[32]

Although Herschel continued to say this new object was a comet, other astronomers had already begun to think otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to calculate the orbit of the new object.[33] Its nearly circular orbit showed him 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".[34] Bode concluded that its near-circular orbit was more like a planet's than a comet's.[35]

The object was soon widely 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."[36] In recognition of his achievement, King George III gave Herschel £200 per year on condition that he move to Windsor so that the Royal Family could look through his telescopes (equivalent to £24,000 in 2019).[37][38]

Exploring

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In 1986, NASA's Voyager 2 visited Uranus. This is the only space probe that tried to see the planet from a short distance. The spacecraft studied the atmosphere of the planet.[39]

Features

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Moons

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Uranus has 27 known moons. They are named for characters from the works of Shakespeare and Alexander Pope.[40][41] The five biggest moons are Miranda, Ariel, Umbriel, Titania and Oberon. It is likely that more moons will be found.

Clouds

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Uranus is covered in blue clouds. The top clouds, made of methane, are hard to see.[42] Lower clouds are thought to be frozen water. There are also violent storms. Wind speeds can reach 250 metres per second (900 km/h; 560 mph). Scientists are studying the clouds to try to understand the storms on the planet.[43]

Rings

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The planet Uranus has a system made of 13 rings, which is far fewer than the rings of Saturn but more than those around Jupiter and Neptune. The rings of Uranus were discovered in 1977.[44] More than 200 years ago, William Herschel also said he saw rings, but today astronomers do not believe that he saw them, because they are very dark and hard to see. Two inner rings were discovered in 1986 in images taken by Voyager 2,[45] and two outer rings were found in 2003–2005 by the Hubble Space Telescope.[46] The rings are probably made of ice.

A lot of people think the rings of Uranus are quite new. They say that the rings are less than 600 million years old. The planet's ring system probably came from when some of its moons crashed together. After crashing, the moons probably broke up into many small pieces of rock and ice, which orbited Uranus and turned into rings.

 
The scheme of Uranus's ring-moon system. Solid lines denote rings; dashed lines denote orbits of moons

General properties

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The ring system of Uranus has thirteen rings. In order of how close they are to Uranus, the rings are 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. There are three groups: nine small main rings (6, 5, 4, α, β, η, γ, δ, ε), two dusty rings (1986U2R/ζ, λ) and two outer rings (μ, ν). The rings of Uranus consist mainly of macroscopic (or visible) particles and less dust, although people know dust is in 1986U2R/ζ, η, δ, λ, ν and μ rings.

There also may be a lot of thin dust bands and faint rings between them. These faint rings and dust bands may stay for only a short time. Some of them became visible during a series of ring events in 2007 when the rings were at different angles.[47] Many dust bands between the rings were seen by Voyager 2. All rings of Uranus have different brightnesses.

The rings are made of somethng that is super dark. The rings are slightly red in the ultraviolet and visible parts of the spectrum and grey in near-infrared.[48] The chemical composition of the ring particles is not known. However, they cannot be made of pure water ice like the rings of Saturn because they are too dark, darker than the inner moons of Uranus. So they are probably a mixture of ice and a dark material. It is hard to know what this material is, but scientists think it may be organic compounds that were darkened by charged particle irradiation from the planet's magnetosphere. The rings' particles may by made of a crushed material, which the inner moons used to be made of.[48]

 
A 1998 false-colour near-infrared image of Uranus showing cloud bands, rings, and moons obtained by the Hubble Space Telescope's NICMOS camera

The ring system of Uranus is not like the faint dusty rings of Jupiter or the big rings of Saturn, some that are very bright because of water ice. However, some parts of their ring systems are close to being the same. The Saturnian F ring and the ε ring are both thin, dark and are shepherded by a pair of moons. The newly discovered outer rings of Uranus are similar to the outer G and E rings of Saturn. Smaller rings existing in the wide Saturnian rings also look like the thin rings of Uranus. Also, dust bands seen between the main rings of Uranus may be like the rings of Jupiter. The Neptunian ring system is a little bit like Uranus's one, although it is smaller, darker and contains more dust. The Neptunian rings are also further from their planet.

Orbit and rotation

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William Herschel, discoverer of Uranus in 1781

Uranus goes around the Sun completely every 84 Earth years. Its normal distance from the Sun is around 3 billion km (about 20 AU). The amount of sunlight on Uranus is about 1/400, or 0.25% of that on Earth.[49] Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace.[50] With time, changes began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first said that the differences might be because of the gravity of another planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On September 23, 1846, Johann Gottfried Galle found a new planet, later called Neptune, close to the area Le Verrier said it would be.[51]

The time it takes for the inside of Uranus to spin around itself is 17 hours and 14 minutes, clockwise (retrograde). Like all giant planets, its upper atmosphere has very strong winds in the direction that the planet rotates. At some latitudes, such as about two-thirds between the equator and the south pole, the parts of the atmosphere we can see move much faster, making a full rotation in just 14 hours.[52]

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References

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  1. ↑ "Uranus". Oxford English Dictionary. Oxford University Press. 2nd ed. 1989.
  2. ↑ Because the vowel a is short in both Greek and Latin, the former pronunciation, /ˈjʊərənəs/, 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.
  3. ↑ "Uranian". Oxford English Dictionary. Oxford University Press. 2nd ed. 1989.
  4. ↑ 4.0 4.1 4.2 Munsell, Kirk (14 May 2007). "NASA: Solar System Exploration: Planets: Uranus: Facts & Figures". NASA. Archived from the original on 14 December 2003. Retrieved 13 August 2007.
  5. ↑ 5.0 5.1 Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on 28 July 2011. Retrieved 13 August 2009.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 Williams, Dr. David R. (31 January 2005). "Uranus Fact Sheet". NASA. Archived from the original on 13 July 2017. Retrieved 10 August 2007.
  7. ↑ Souami, D.; Souchay, J. (July 2012). "The solar system's invariable plane". Astronomy & Astrophysics. 543: 11. Bibcode:2012A&A...543A.133S. doi:10.1051/0004-6361/201219011. A133.
  8. ↑ 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
  9. ↑ "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 2021-09-07.
  10. ↑ Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–683. Bibcode:1994A&A...282..663S.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 Seidelmann, P. Kenneth; Archinal, Brent A.; A'Hearn, Michael F.; et al. (2007). "Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006". Celestial Mechanics and Dynamical Astronomy. 98 (3): 155–180. Bibcode:2007CeMDA..98..155S. doi:10.1007/s10569-007-9072-y. S2CID 122772353.
  12. ↑ Jacobson, R. A.; Campbell, J. K.; Taylor, A. H.; Synnott, S. P. (June 1992). "The masses of Uranus and its major satellites from Voyager tracking data and earth-based Uranian satellite data". The Astronomical Journal. 103 (6): 2068–2078. Bibcode:1992AJ....103.2068J. doi:10.1086/116211.
  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. ↑ Pearl, J.C.; et al. (1990). "The albedo, effective temperature, and energy balance of Uranus, as determined from Voyager IRIS data". Icarus. 84 (1): 12–28. Bibcode:1990Icar...84...12P. doi:10.1016/0019-1035(90)90155-3.
  15. ↑ Mallama, Anthony; Krobusek, Bruce; Pavlov, Hristo (2017). "Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine". Icarus. 282: 19–33. arXiv:1609.05048. Bibcode:2017Icar..282...19M. doi:10.1016/j.icarus.2016.09.023. S2CID 119307693.
  16. ↑ Podolak, M.; Weizman, A.; Marley, M. (December 1995). "Comparative models of Uranus and Neptune". Planetary and Space Science. 43 (12): 1517–1522. Bibcode:1995P&SS...43.1517P. doi:10.1016/0032-0633(95)00061-5.
  17. ↑ 17.0 17.1 Lunine, Jonathan I. (September 1993). "The Atmospheres of Uranus and Neptune". Annual Review of Astronomy and Astrophysics. 31: 217–263. Bibcode:1993ARA&A..31..217L. doi:10.1146/annurev.aa.31.090193.001245.
  18. ↑ 18.0 18.1 Mallama, A.; Hilton, J.L. (2018). "Computing Apparent Planetary Magnitudes for The Astronomical Almanac". Astronomy and Computing. 25: 10–24. arXiv:1808.01973. Bibcode:2018A&C....25...10M. doi:10.1016/j.ascom.2018.08.002. S2CID 69912809.
  19. ↑ Irwin, Patrick G. J.; et al. (23 April 2018). "Detection of hydrogen sulfide above the clouds in Uranus's atmosphere" (PDF). Nature Astronomy. 2 (5): 420–427. Bibcode:2018NatAs...2..420I. doi:10.1038/s41550-018-0432-1. hdl:2381/42547. ISSN 2397-3366. S2CID 102775371. Archived from the original (PDF) on 28 April 2019. Retrieved 25 August 2019.
  20. ↑ Lindal, G. F.; Lyons, J. R.; Sweetnam, D. N.; Eshleman, V. R.; Hinson, D. P.; Tyler, G. L. (30 December 1987). "The Atmosphere of Uranus: Results of Radio Occultation Measurements with Voyager 2". Journal of Geophysical Research. 92 (A13): 14, 987–15, 001. Bibcode:1987JGR....9214987L. doi:10.1029/JA092iA13p14987. ISSN 0148-0227.
  21. ↑ Conrath, B.; Gautier, D.; Hanel, R.; Lindal, G.; Marten, A. (1987). "The Helium Abundance of Uranus from Voyager Measurements". Journal of Geophysical Research. 92 (A13): 15003–15010. Bibcode:1987JGR....9215003C. doi:10.1029/JA092iA13p15003.
  22. ↑ Its north and south poles, therefore, lie where most other planets have their equators. Smith B.A. 1986. Voyager 2 in the Uranian system: imaging science results. Science 233 (4759): 43–64. record/ 1230972#.Xcgi81f7SUk
  23. ↑ library.thinkquest.org/C005921/Uranus/uranLocOrb.htm
  24. ↑ Gay, Peter; Time-Life Books (1966). "The Practical Philosophers". Age of Enlightenment. Time. p. 25.
  25. ↑ Burkert 2005, p. 295.
  26. ↑ "Bath Preservation Trust". Retrieved 29 September 2007.
  27. ↑ Herschel, William; Watson, Dr. (1781). "Account of a Comet, By Mr. Herschel, F. R. S.; Communicated by Dr. Watson, Jun. of Bath, F. R. S". Philosophical Transactions of the Royal Society of London. 71: 492–501. Bibcode:1781RSPT...71..492H. doi:10.1098/rstl.1781.0056. S2CID 186208953.
  28. ↑ 28.0 28.1 28.2 Journal of the Royal Society and Royal Astronomical Society 1, 30, quoted in Miner[broken anchor], p. 8.
  29. ↑ "Ice Giants: The Discovery of Nepture and Uranus". Sky & Telescope. American Astronomical Society. 29 July 2020. Retrieved 21 November 2020.
  30. ↑ Royal Astronomical Society MSS W.2/1.2, 23; quoted in Miner[broken anchor] p. 8.
  31. ↑ RAS MSS Herschel W.2/1.2, 24, quoted in Miner[broken anchor] p. 8.
  32. ↑ RAS MSS Herschel W1/13.M, 14 quoted in Miner[broken anchor] p. 8.
  33. ↑ Lexell, A. J. (1787). "Recherches sur la nouvelle Planète, découverte par M. Herschel & nommée par lui Georgium Sidus". Nova Acta Academiae Scientiarum Imperialis Petropolitanae (1): 69–82.
  34. ↑ Johann Elert Bode, Berliner Astronomisches Jahrbuch, p. 210, 1781, quoted in Miner[broken anchor], p. 11.
  35. ↑ Miner[broken anchor], p. 11.
  36. ↑ Dreyer, J. L. E. (1912). The Scientific Papers of Sir William Herschel. Vol. 1. Royal Society and Royal Astronomical Society. p. 100. ISBN 978-1-84371-022-6.
  37. ↑ UK Retail Price Index inflation figures are based on data from Clark, Gregory (2017). "The Annual RPI and Average Earnings for Britain, 1209 to Present (New Series)". MeasuringWorth. Retrieved January 27, 2019.
  38. ↑ Miner[broken anchor], p. 12
  39. ↑ Tyler, J.L.; Sweetnam, D.N.; Anderson, J.D.; Campbell, J. K.; Eshleman, V. R.; Hinson, D. P.; Levy, G. S.; Lindal, G. F.; Marouf, E. A.; Simpson, R. A. (1986). "Voyger 2 Radio Science Observations of the Uranian System: Atmosphere, Rings, and Satellites". Science. 233 (4759): 79–84.
  40. ↑ Faure, Gunter; Mensing, Teresa (2007). "Uranus: What Happened Here?". In Faure, Gunter; Mensing, Teresa M. (eds.). Introduction to Planetary Science. Springer Netherlands. pp. 369–384. doi:10.1007/978-1-4020-5544-7_18. ISBN 978-1-4020-5233-0.
  41. ↑ "Uranus". nineplanets.org. Retrieved 2007-07-03.
  42. ↑ "Uranus Clouds, overview". windows.ucar.edu. Archived from the original on 22 March 2009. Retrieved 29 March 2010.
  43. ↑ "SPACE.com -- New Images Reveal Clouds on Planet Uranus". space.com. 10 November 2004. Retrieved 29 March 2010.
  44. ↑ Elliot J.L; Dunham, E.; Mink D. (1977). "The rings of Uranus". Cornell University. 267 (5609): 328–330. Bibcode:1977Natur.267..328E. doi:10.1038/267328a0. S2CID 4194104. Retrieved June 9, 2007.
  45. ↑ Smith, B.A.; Soderblom L.A.; et al. (1986). "Voyager 2 in the Uranian system: Imaging Science results". Science. 233 (4759): 97–102. Bibcode:1986Sci...233...43S. doi:10.1126/science.233.4759.43. PMID 17812889. S2CID 5895824.
  46. ↑ "NASA's Hubble discovers new rings and moons around Uranus". Hubblesite. 2005. Retrieved June 9, 2007.
  47. ↑ de Pater, Imke; Hammel H.B.; et al. (2007). "The dark side of the rings of Uranus". Science. 317 (5846): 1888–1890. Bibcode:2007Sci...317.1888D. doi:10.1126/science.1148103. PMID 17717152. S2CID 23875293.
  48. ↑ 48.0 48.1 Baines, Kevin H.; et al. (1998). "Near-Infrared absolute photometric imaging of the Uranian system". Icarus. 132 (2): 266–284. Bibcode:1998Icar..132..266B. doi:10.1006/icar.1998.5894.
  49. ↑ "Next Stop Uranus". 1986. Retrieved June 9, 2007.
  50. ↑ Forbes, George 1909. History of Astronomy.
  51. ↑ O'Connor J.J. and Robertson E.F. (1996). "Mathematical discovery of planets". Archived from the original on June 12, 2015. Retrieved June 13, 2007.
  52. ↑ Peter J. Gierasch and Philip D. Nicholson (2004). "Uranus". NASA World Book. Archived from the original on August 11, 2011. Retrieved June 9, 2007.

Notes

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  1. ↑ These are the mean elements from VSOP87, together with derived quantities.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 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.

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