Neptune

Neptune is the eighth and farthest planet from the Sun in the Solar System. It is an ice giant. It is the fourth-largest planet in the system.

Quick Facts Discovery, Discovered by ...

Neptune , historically also

Neptune in true color[lower-alpha 1] as captured by Voyager 2. Like Uranus, Neptune has a muted appearance; several storms can still be seen, such as the Great Dark Spot at the center.
Discovery[1]
Discovered by	Johann Galle Urbain Le Verrier John Couch Adams
Discovery date	23 September 1846
Designations
Pronunciation	US: /ˈnɛptuːn/ (listen), UK: /-tjuːn/[2]
Named after	Latin Neptunus, via French Neptune
Adjectives	Neptunian (/nɛpˈtjuːniən/),[3] Poseidean[4]
Orbital characteristics[5][lower-alpha 2]
Epoch J2000
Aphelion	30.33 AU (4.54 billion km)
Perihelion	29.81 AU (4.46 billion km)
Semi-major axis	30.07 AU (4.50 billion km)
Eccentricity	0.008678
Orbital period	164.8 yr 60,195 days 89,666 Neptunian solar days[6]
Synodic period	367.49 days[7]
Average orbital speed	5.43 km/s[7]
Mean anomaly	259.883°
Inclination	1.770° to ecliptic 6.43° to Sun's equator 0.74° to invariable plane[8]
Longitude of ascending node	131.783°
Time of periastron	2042-Sep-04[9]
Argument of perihelion	273.187°
Known satellites	16
Physical characteristics
Mean radius	24,622±19 km[10][lower-alpha 3]
Equatorial radius	24,764±15 km[10][lower-alpha 3] 3.883 Earths
Polar radius	24,341±30 km[10][lower-alpha 3] 3.829 Earths
Flattening	0.0171±0.0013
Surface area	7.6187×109 km2[11][lower-alpha 3] 14.98 Earths
Volume	6.253×1013 km3[7][lower-alpha 3] 57.74 Earths
Mass	1.02413×1026 kg[7] 17.147 Earths 5.15×10−5 Suns
Mean density	1.638 g/cm3[7][lower-alpha 4]
Surface gravity	11.15 m/s2[7][lower-alpha 3] 1.14 g
Moment of inertia factor	0.23[12] (estimate)
Escape velocity	23.5 km/s[7][lower-alpha 3]
Rotation period	0.67125 d 16 h 6 m 36 s[6]
Sidereal rotation period	0.6713 day[7] 16 h 6 min 36 s
Equatorial rotation velocity	2.68 km/s (9,650 km/h)
Axial tilt	28.32° (to orbit)[7]
North pole right ascension	19h 57m 20s[10] 299.3°
North pole declination	42.950°[10]
Albedo	0.290 (bond)[13] 0.442 (geom.)[14]
Surface temp. min mean max 1 bar level 72 K (−201 °C)[7] 0.1 bar (10 kPa) 55 K (−218 °C)[7]
Apparent magnitude	7.67[15] to 8.00[15]
Absolute magnitude (H)	−6.9[16]
Angular diameter	2.2–2.4″[7][17]
Atmosphere[7]
Scale height	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: ammonia water ice ammonium hydrosulfide methane ice (?)

Close

Neptune's mass is 17 times Earth's mass and a little bit more than Uranus' mass. Neptune is denser and smaller than Uranus. Because of its greater mass, Neptune's gravity makes its atmosphere smaller and denser.

It was named after the Roman god of the sea, Neptune. Neptune's astronomical symbol is ♆, the trident of the god Neptune.

Neptune's atmosphere is mostly hydrogen and helium. It also contains small amounts of methane which makes the planet appear blue.^[18][19][20] Neptune's blue color is similar, but slightly darker, than the color of Uranus. Neptune also has the strongest winds of any planet in the Solar System, as high as 2,100 km/h or 1,300 mph.

Urbain Le Verrier and John Couch Adams were the astronomers who discovered Neptune. Neptune was not discovered using a telescope. It was the first planet to be discovered using mathematics. In 1821, astronomers saw that Uranus' orbit was different from what they expected. Another nearby planet's mass was changing Uranus' orbit. They found Neptune was the cause.

Voyager 2 visited Neptune on 25 August 1989. It was the only spacecraft to visit the planet. Neptune used to have a huge storm known as the "Great Dark Spot". Voyager 2 discovered the spot in 1989. The dark spot was not seen in 1994, but new spots were found since then. It is not known why the dark spot disappeared. Visits by other space probes have been planned.

Neptune has five rings surrounding it. However, that is hard to see from Earth. Even though it is the furthest planet away from the sun it is not the coldest