Neptune
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Neptune
Discovery
Discovered by
Urbain Le Verrier* Johann Galle
Discovery date
23 September 1846
Designations
Pronunciation
i/'n?ptu?n/
/'n?ptju?n/
Adjectives
Neptunian
Orbital characteristics
Epoch J2000
Aphelion
7012453758092238114?30.331855 AU
(7012453758090000000?4537580900 km)
Perihelion
7012445950444728198?29.809946 AU
(7012445950440000000?4459504400 km)
7012449854261003263?30.070900 AU
(7012449854260000000?4498542600 km)
Eccentricity
6997867797000000000?0.00867797
164.8 yr
7009520041859200000?60190.03 d
7004896660000000000?89666 Neptunian solar days
367.49 days
5.43 km/s
7000453585918908147?259.885588°
Inclination
6998308569848429468?1.767975° to ecliptic
6.43° to Sun's equator
0.72° to invariable plane
7000230004679437008?131.782974°
7000476857835466950?273.219414°
Known satellites
14
Physical characteristics
7007246220000000000?24622±19 km
7007247640000000000?24764±15 km
3.883 Earths
7007243410000000000?24341±30 km
3.829 Earths
Flattening
6998171000000000000?0.0171±0.0013
7015761830000000000?7.6183×109 km2
14.98 Earths
Volume
7022625399999999999?6.254×1013 km3
57.74 Earths
Mass
7026102430000000000?1.0243×1026 kg
17.147 Earths
5.15×10-5 Suns
7003163800000000000?1.638 g/cm3
11.15 m/s2
1.14 g
23.5 km/s
0.6713 day
16 h 6 min 36 s
2.68 km/s
7003268333333333333?9660 km/h
28.32°
19h 57m 20s
299.3°
42.950°
Albedo
0.290 (bond)
0.41 (geom.)
Surface temp.
min
mean
max
1 bar level
72 K (-201 °C)
0.1 bar (10 kPa)
55 K
8.02 to 7.78
2.2–2.4?
Atmosphere
19.7 ± 0.6 km
Composition by volume
80 ± 3.2% hydrogen (H2)
19 ± 3.2% helium (He)
1.5 ± 0.5% methane (CH4)
~0.019% hydrogen deuteride (HD)
~0.00015% ethane (C2H6)
Ices:
ammonia (NH3)
water (H2O)
ammonium hydrosulfide (NH4SH)
methane ice (?) (CH4•5.75H2O)
Neptune is the eighth and farthest planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Among the giant planets in the Solar System, Neptune is the most dense. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth, and not as dense as Neptune. Neptune orbits the Sun at an average distance of 30.1 astronomical units (4.50×109 km). Named after the Roman god of the sea, its astronomical symbol is ?, a stylised version of the god Neptune's trident.Neptune is not visible to the unaided eye and is the only planet found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 13 moons were located telescopically until the 20th century. The planet's distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989. The advent of Hubble Space Telescope and large ground-based telescopes with adaptive optics has allowed for more-detailed observations.Neptune is similar in composition to Uranus, and both have compositions that differ from those of the larger gas giants, Jupiter and Saturn. Neptune's atmosphere, like Jupiter's and Saturn's, is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen; it contains a higher proportion of "ices" such as water, ammonia, and methane. Scientists sometimes categorise Uranus and Neptune as "ice giants" to emphasise this distinction. The interior of Neptune, like that of Uranus, is primarily composed of ices and rock. Traces of methane in the outermost regions in part account for the planet's blue appearance.In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has active and visible weather patterns. For example, at the time of the 1989 Voyager 2 flyby, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 kilometres per hour (580 m/s; 1,300 mph). 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). Temperatures at the planet's centre are approximately 5,400 K (5,100 °C). Neptune has a faint and fragmented ring system (labelled "arcs"), which may have been detected during the 1960s but was indisputably confirmed only in 1989 by Voyager 2.
^ a b Hamilton, Calvin J. (4 August 2001). "Neptune". Views of the Solar System. Retrieved 13 August 2007.
^ Walter, Elizabeth (21 April 2003). Cambridge Advanced Learner's Dictionary (2nd ed.). Cambridge University Press. ISBN 978-0-521-53106-1.
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^ Seligman, Courtney. "Rotation Period and Day Length". Retrieved 13 August 2009.
^ a b c d e f g h i j k l m n o Williams, David R. (1 September 2004). "Neptune Fact Sheet". NASA. Retrieved 14 August 2007.
^ "The MeanPlane (Invariable plane) of the Solar System passing through the barycenter". 3 April 2009. Retrieved 10 April 2009. (produced with Solex 10 written by Aldo Vitagliano; see also Invariable plane)
^ Yeomans, Donald K. "HORIZONS Web-Interface for Neptune Barycenter (Major Body=8)". JPL Horizons On-Line Ephemeris System. 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)".)
^ Cite error: The named reference Seidelmann_Archinal_A.27hearn_et_al._2007 was invoked but never defined (see the help page).
^ Cite error: The named reference ephemeris was invoked but never defined (see the help page).
^ Chang, Kenneth (18 October 2014). "Dark Spots in Our Knowledge of Neptune". New York Times. Retrieved 21 October 2014.
^ Cite error: The named reference Lunine_1993 was invoked but never defined (see the help page).
^ Cite error: The named reference Podolak_Weizman_et_al._1995 was invoked but never defined (see the help page).
^ Munsell, Kirk; Smith, Harman; Harvey, Samantha (13 November 2007). "Neptune overview". Solar System Exploration. NASA. Retrieved 20 February 2008.
^ Suomi, V. E.; Limaye, S. S.; Johnson, D. R. (1991). "High Winds of Neptune: A possible mechanism". Science 251 (4996): 929–932. Bibcode:1991Sci...251..929S. doi:10.1126/science.251.4996.929. PMID 17847386.
^ Cite error: The named reference hubbard was invoked but never defined (see the help page).
^ Cite error: The named reference nettelmann was invoked but never defined (see the help page).
^ Cite error: The named reference ring1 was invoked but never defined (see the help page).
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