Neptune
 
Neptune information
Average distance from Sun:4498252900 km (30.0685 AU)
Perihelion (closest):4459630000 km
Perihelion (farthest):4536870000 km
Equatorial radius:24764 km (Diameter: 49528 km)
Equatorial circumference:155597 km
Volume:62526000000000 km²
Mass:102440000000000000000000000 kg
Density:1.76 g/cm³
Surface area:7640800000 km²
Equatorial surface gravity:10.71 m/s²
Escape velocity:23710 m/s
Siderial rotation period (length of day):16.11 earth hours
Siderial orbit period (length of year):60190 earth days
Mean orbit velocity:5477.8 m/s
Orbital eccentricity:0.00859
Orbital inclination to ecliptic:1.769 degrees
Equatorial inclination to orbit:29.58 degrees
Orbital circumference:28142000000 km
Surface temperature (min/max):59 K
Atmospheric constituents:H2, He, CH4
 Neptune, Sun VIII
 
Neptune

In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea.

After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton's laws. It was therefore predicted that another more distant planet must be perturbing Uranus' orbit. Neptune was first observed by Galle and d'Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. An international dispute arose between the English and French (though not, apparently between Adams and Le Verrier personally) over priority and the right to name the new planet; they are now jointly credited with Neptune's discovery. Subsequent observations have shown that the orbits calculated by Adams and Le Verrier diverge from Neptune's actual orbit fairly quickly. Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location.

More than two centuries earlier, in 1613, Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. On two successive nights he actually noticed that it moved slightly with respect to another nearby star. But on the subsequent nights it was out of his field of view. Had he seen it on the previous few nights Neptune's motion would have been obvious to him. But, alas, cloudy skies prevented obsevations on those few critical days.

Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. Much of we know about Neptune comes from this single encounter. But fortunately, recent ground-based and HST observations have added a great deal, too.

Because Pluto's orbit is so eccentric, it sometimes crosses the orbit of Neptune making Neptune the most distant planet from the Sun for a few years.

Neptune's composition is probably similar to Uranus': various 'ices' and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it may not have a distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core (about the mass of the Earth) of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane.

Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint.

Like a typical gas planet, Neptune has rapid winds confined to bands of latitude and large storms or vortices. Neptune's winds are the fastest in the solar system, reaching 2000 km/hour.

Like Jupiter and Saturn, Neptune has an internal heat source -- it radiates more than twice as much energy as it receives from the Sun.

At the time of the Voyager encounter, Neptune's most prominent feature was the Great Dark Spot (left) in the southern hemisphere. It was about half the size as Jupiter's Great Red Spot (about the same diameter as Earth). Neptune's winds blew the Great Dark Spot westward at 300 meters/second (700 mph). Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune every 16 hours or so now known as 'The Scooter' (right). It may be a plume rising from lower in the atmosphere but its true nature remains a mystery.

However, HST observations of Neptune (left) in 1994 show that the Great Dark Spot has disappeared! It has either simply dissipated or is currently being masked by other aspects of the atmosphere. A few months later HST discovered a new dark spot in Neptune's northern hemisphere. This indicates that Neptune's atmosphere changes rapidly, perhaps due to slight changes in the temperature differences between the tops and bottoms of the clouds.

Neptune also has rings. Earth-based observations showed only faint arcs instead of complete rings, but Voyager 2's images showed them to be complete rings with bright clumps. One of the rings appears to have a curious twisted structure (right).

Like Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown.

Neptune's rings have been given names: the outermost is Adams (which contains three prominent arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago), and finally the faint but broad Galle.

Neptune's magnetic field is, like Uranus', oddly oriented and probably generated by motions of conductive material (probably water) in its middle layers.

Neptune can be seen with binoculars (if you know exactly where to look) but a large telescope is needed to see anything other than a tiny disk. There are several Web sites that show the current position of Neptune (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program.

Neptune's Satellites



Neptune has 13 known moons; 7 small named ones and Triton plus four discovered in 2002 and one discovered in 2003 which have yet to be named.

Neptune's Rings



RingDistance
(km)		Width
(km)		aka
Diffuse41900151989N3R, Galle
Inner53200151989N2R, LeVerrier
Plateau5320058001989N4R, Lassell, Arago
Main62930< 501989N1R, Adams


(distance is from Neptune's center to the ring's inner edge)
 
Satellites of Neptune
SatelliteDistance
(km)		Radius
(km)		Mass
(kg)		DiscovererYear
Naiad4823000048 x 30 x 26200000000000Voyager 21989
Thalassa5007000054 x 50 x 26400000000000R. Terrile1989
Despina5253000090 x 74 x 642000000000000S. Synnott1989
Galatea61950000102 x 92 x 724000000000000S. Synnott1989
Larissa73550000108 x 102 x 845000000000000H. Reitsema1982
Proteus117650000220 x 208 x 20250000000000000S. Synnott1989
Triton3547600001353.421400000000000000W. Lassell1846
Nereid551340000017030000000000000G. Kuiper1949
S/2002N115686000000241000000000002002
S/2002N222452000000241000000000002002
S/2002N322580000000241000000000002002
Psamathe4673800000014200000000002003
S/2002N446570000000302002
 
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