Neptune

This article is about the planet. For the Roman god, see Neptune (mythology). For other uses, see Neptune (disambiguation).

Neptune
Neptune in true colour[1] as captured by Voyager 2. Like Uranus, Neptune has a muted appearance; several storms can still be seen, such as Great Dark Spot GDS-89[a] at the center
Discovery[2]
Discovered by
Discovery date23 September 1846
Designations
PronunciationUS: /ˈnɛptuːn/ ⓘ, UK: /-tjuːn/[3]
Named after
Latin Neptunus, via French Neptune
AdjectivesNeptunian (/nɛpˈtjuːniən/),[4] Poseidean[5]
Symbol♆, ⯉
Orbital characteristics[6][b]
Epoch J2000
Aphelion30.33 AU (4.54 billion km)
Perihelion29.81 AU (4.46 billion km)
30.07 AU (4.50 billion km)
Eccentricity0.008678
367.49 days[8]
5.43 km/s[8]
259.883°
Inclination1.770° to ecliptic
6.43° to Sun's equator
0.74° to invariable plane[9]
131.783°
2042-Sep-04[10]
273.187°
Known satellites16
Physical characteristics
24,622±19 km[11][c]
Equatorial radius
24,764±15 km[11][c]
3.883 Earths
Polar radius
24,341±30 km[11][c]
3.829 Earths
Flattening0.0171±0.0013
7.6187×109 km2[12][c]
14.98 Earths
Volume6.253×1013 km3[8][c]
57.74 Earths
Mass1.02409×1026 kg[8]
17.147 Earths
5.15×10−5 Suns
Mean density
1.638 g/cm3[8][d]
11.15 m/s2 (1.137 g0)[8][c]
0.23[13] (estimate)
23.5 km/s[8][c]
0.67125 d
16 h 6 m 36 s[7]
0.6713 day[8]
16 h 6 min 36 s
Equatorial rotation velocity
2.68 km/s[14]
28.32° (to orbit)[8]
North pole right ascension
19h 57m 20s[11]
299.36° [15]
North pole declination
43.46° [15]
Albedo0.290 (bond)[16]
0.442 (geom.)[17]
Surface temp. min mean max
1 bar level 72 K (−201 °C)[8]
0.1 bar (10 kPa) 55 K (−218 °C)[8]
7.67[18] to 8.00[18]
−6.9[19]
2.2–2.4″[8][20]
Atmosphere[8]
19.7±0.6 km
Composition by volume
  • 80%±3.2% hydrogen
  • 19%±3.2% helium
  • 1.5%±0.5% methane
  • ~0.019% hydrogen deuteride
  • ~0.00015% ethane
  • Icy volatiles:

Neptune is the eighth and farthest known planet from the Sun. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth. Compared to its fellow ice giant Uranus, Neptune is slightly more massive, but denser and smaller. Being composed primarily of gases and liquids,[21] it has no well-defined solid surface, and orbits the Sun once every 164.8 years at an orbital distance of 30.1 astronomical units (4.5 billion kilometres; 2.8 billion miles). It is named after the Roman god of the sea and has the astronomical symbol ♆, representing Neptune's trident.[e]

Neptune is not visible to the unaided eye and is the only planet in the Solar System that was found from mathematical predictions derived from indirect observations rather than being initially observed by direct empirical observation, when unexpected changes in the orbit of Uranus led Alexis Bouvard to hypothesise that its orbit was subject to gravitational perturbation by an unknown planet. After Bouvard's death, the position of Neptune was predicted from his observations, independently, by John Couch Adams and Urbain Le Verrier. Neptune was subsequently directly observed with a telescope on 23 September 1846[2] by Johann Gottfried Galle within a degree of the position predicted by Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining moons were located telescopically until the 20th century.

The planet's distance from Earth gives it a small apparent size, and its distance from the Sun renders it very dim, making it challenging to study with Earth-based telescopes. Only the advent of the Hubble Space Telescope and of large ground-based telescopes with adaptive optics allowed for detailed observations. Neptune was visited by Voyager 2, which flew by the planet on 25 August 1989; Voyager 2 remains the only spacecraft to have visited it.[22][23] Like the gas giants (Jupiter and Saturn), Neptune's atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but contains a higher proportion of ices such as water, ammonia and methane. Similar to Uranus, its interior is primarily composed of ices and rock;[24] both planets are normally considered "ice giants" to distinguish them.[25] Along with Rayleigh scattering, traces of methane in the outermost regions make Neptune appear faintly blue.[26][27]

In contrast to the strongly seasonal atmosphere of Uranus, which can be featureless for long periods of time, Neptune's atmosphere has active and consistently visible weather patterns. At the time of the Voyager 2 flyby in 1989, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. In 2018, a newer main dark spot and smaller dark spot were identified and studied.[28] These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, as high as 2,100 km/h (580 m/s; 1,300 mph).[29] Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K (−218 °C; −361 °F). Temperatures at the planet's centre are approximately 5,400 K (5,100 °C; 9,300 °F).[30][31] Neptune has a faint and fragmented ring system (labelled "arcs"), discovered in 1984 and confirmed by Voyager 2.[32]

  1. ^ Irwin, Patrick G. J.; Dobinson, Jack; James, Arjuna; Teanby, Nicholas A.; Simon, Amy A.; Fletcher, Leigh N.; Roman, Michael T.; Orton, Glenn S.; Wong, Michael H.; Toledo, Daniel; Pérez-Hoyos, Santiago; Beck, Julie (23 December 2023). "Modelling the seasonal cycle of Uranus's colour and magnitude, and comparison with Neptune". Monthly Notices of the Royal Astronomical Society. 527 (4): 11521–11538. doi:10.1093/mnras/stad3761. hdl:20.500.11850/657542.
  2. ^ a b Hamilton, Calvin J. (4 August 2001). "Neptune". Views of the Solar System. Archived from the original on 15 July 2007. Retrieved 13 August 2007.
  3. ^ Walter, Elizabeth (21 April 2003). "Neptune". Cambridge Advanced Learner's Dictionary (2nd ed.). Cambridge University Press. ISBN 978-0-521-53106-1.
  4. ^ "Neptunian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  5. ^ "Enabling Exploration with Small Radioisotope Power Systems" (PDF). NASA. September 2004. Archived from the original (PDF) on 22 December 2016. Retrieved 26 January 2016.
  6. ^ Yeomans, Donald K. "HORIZONS Web-Interface for Neptune Barycenter (Major Body=8)". JPL Horizons On-Line Ephemeris System. Archived from the original on 7 September 2021. Retrieved 18 July 2014.—Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Neptune Barycenter" and "Center: Solar System Barycenter (@0)".)
  7. ^ a b Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on 28 July 2011. Retrieved 13 August 2009.
  8. ^ a b c d e f g h i j k l m Williams, David R. (1 September 2004). "Neptune Fact Sheet". NASA. Archived from the original on 1 July 2010. Retrieved 14 August 2007.
  9. ^ 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.
  10. ^ "HORIZONS Planet-center Batch call for September 2042 Perihelion". ssd.jpl.nasa.gov (Perihelion for Neptune's planet-center (899) occurs on 2042-Sep-04 at 29.80647406au 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 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 fact2 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 978-0-521-85371-2. Archived from the original on 26 November 2016. Retrieved 17 August 2016.
  14. ^ Kennett, Carolyn (2022). Uranus and Neptune. Reaktion Books. p. 185. ISBN 978-1-78914-642-4.
  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.
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  17. ^ Cite error: The named reference Mallama_et_al was invoked but never defined (see the help page).
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  19. ^ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on 24 July 2023. Retrieved 29 May 2023.
  20. ^ Espenak, Fred (20 July 2005). "Twelve Year Planetary Ephemeris: 1995–2006". NASA. Archived from the original on 5 December 2012. Retrieved 1 March 2008.
  21. ^ "Neptune". NASA Science. 10 November 2017. Retrieved 19 July 2024.
  22. ^ Chang, Kenneth (18 October 2014). "Dark Spots in Our Knowledge of Neptune". The New York Times. Archived from the original on 28 October 2014. Retrieved 21 October 2014.
  23. ^ "Exploration | Neptune". NASA Solar System Exploration. Archived from the original on 17 July 2020. Retrieved 3 February 2020. In 1989, NASA's Voyager 2 became the first-and only-spacecraft to study Neptune up close.
  24. ^ Cite error: The named reference Podolak Weizman et al. 1995 was invoked but never defined (see the help page).
  25. ^ Cite error: The named reference Lunine 1993 was invoked but never defined (see the help page).
  26. ^ Munsell, Kirk; Smith, Harman; Harvey, Samantha (13 November 2007). "Neptune overview". Solar System Exploration. NASA. Archived from the original on 3 March 2008. Retrieved 20 February 2008.
  27. ^ "Gemini North Telescope Helps Explain Why Uranus and Neptune Are Different Colors - Observations from Gemini Observatory, a Program of NSF's NOIRLab, and other telescopes reveal that excess haze on Uranus makes it paler than Neptune". noirlab.edu. 31 May 2022. Archived from the original on 30 July 2022. Retrieved 30 July 2022.
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  29. ^ Suomi, V.E.; Limaye, S.S.; Johnson, D.R. (1991). "High Winds of Neptune: A possible mechanism". Science. 251 (4996): 929–32. Bibcode:1991Sci...251..929S. doi:10.1126/science.251.4996.929. PMID 17847386. S2CID 46419483.
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  31. ^ Cite error: The named reference nettelmann was invoked but never defined (see the help page).
  32. ^ Cite error: The named reference ring1 was invoked but never defined (see the help page).


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