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Characteristic of Neptune

Neptune is one of the two giant ice planets in the Solar System, and is farthest of the eight major planets from the Sun (Pluto is more of an asteroid than a planet). As with Uranus, Neptune's distance from the Sun and its relatively small size compared to Jupiter and Saturn ensure that the planet is below the freezing point of its main constituents. The radius of the planet is defined as the point in the atmosphere where the pressure equals 1 bar (the pressure at sea level on Earth). Two rotation periods are defined for the planet: the rotation period of its magnetic field, and the rotation implied by its flattening.

In the table that follows, the observed values are taken from Yoder (1995).[1] Go to table of characteristics.

Characteristics of Neptune


6.8351(07±15)×1021 cm3 s−2


1.0241×1029 g

Mean Radius

2.46(24±21)×109 cm

Equatorial Radius

2.47(66±15)×109 cm



Surface Gravity

1127 cm s−2

Escape Velocity

2.356×106 cm s−1

Average Density

1.638 g cm−3

Sidereal Rotation Period

16h 06m

57996±36 s

Sidereal Rotation Period


60120±5040 s

Obliquity to Orbit

29° 33

Sidereal Orbital Period

59799.900 d

Semimajor Axis

30.06896348 AU



Solar Constant

1.47 × 103 ergs cm−2 s−1

[1] Yoder, Charles F. “Astrometric and Geodetic Properties of Earth and the Solar System.” In Global Earth Physics: A Handbook of Physical Constants edited by T.J. Ahrens, 1–31. AGU Reference Shelf, No. 1. Washington: American Geophysical Union, 1995.

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