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Neptune's mass of 1.0243 × 10 26 kg [8] is intermediate between Earth and the larger gas giants: it is 17 times that of Earth but just 1/19th that of Jupiter. [g] Its gravity at 1 bar is 11.15 m/s 2, 1.14 times the surface gravity of Earth, [71] and surpassed only by Jupiter. [72] Neptune's equatorial radius of 24,764 km [11] is nearly four ...
Triton orbits Neptune in a retrograde orbit—revolving in the opposite direction to the parent planet's rotation—the only large moon in the Solar System to do so. [ 3 ] [ 13 ] Triton is thought to have once been a dwarf planet from the Kuiper belt , captured into Neptune's orbit by the latter's gravity .
Naiad, the closest regular moon, is also the second smallest among the inner moons (following the discovery of Hippocamp), whereas Proteus is the largest regular moon and the second largest moon of Neptune. The first five moons orbit much faster than Neptune's rotation itself ranging from 7 hours for Naiad and Thalassa, to 13 hours for Larissa.
For gaseous or fluid bodies, such as stars and giant planets, the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation. Typically, the stated rotation period for a giant planet (such as Jupiter, Saturn, Uranus, Neptune) is its internal rotation period, as determined from the rotation ...
A celestial object's axial tilt indicates whether the object's rotation is prograde or retrograde. Axial tilt is the angle between an object's rotation axis and a line perpendicular to its orbital plane passing through the object's centre. An object with an axial tilt up to 90 degrees is rotating in the same direction as its primary.
The following outline is provided as an overview of and topical guide to Neptune: . Neptune – eighth and farthest known planet from the Sun in the Solar System.In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet.
Each night the planet appeared to lag a little behind the stars, in what is called prograde motion. Near opposition, the planet would appear to reverse and move through the night sky faster than the stars for a time in retrograde motion before reversing again and resuming prograde. Epicyclic theory, in part, sought to explain this behavior.
Nereid, or Neptune II, is the third-largest moon of Neptune. It has the most eccentric orbit of all known moons in the Solar System . [ 4 ] It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.