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[[eo:Neptuno]]

Neptune is the eighth planet from the sun?. It is a [gas giant]?.

Neptune as photographed by NASA's [Voyager 2]? probe. In the summer of 1989, Voyager 2 became the first spacecraft to observe the planet Neptune, its final planetary target. It passed about 4,950 kilometers (3,000 miles) above Neptune's north pole.

After the discovery of Uranus?, it was noted that the orbits of Uranus, Saturn?, and Jupiter? were apparently being perturbed by an additional unknown mass in the outer solar system. [John Couch Adams]? and [Urbain Jean Joseph Le Verrier]? used calculations to predict the region of the sky where the mysterious additional planet was likely to be located, and it was subsequently independantly discovered by the German astronomer [Johann Gottfried Galle]? of Berlin? Observatory on [September 23]? 1846?. Later it was found that Galileo? had much earlier observed Neptune. Evidence of the fact was found in his notes, but he had thought it was a star. Had he observed Neptune only a matter of days earlier, its orbital motion would have been far more obvious. With an orbital period of 165 years, Neptune will first return to the point in its orbit where Galle discovered it in 2011?. Due to Pluto?'s eccentric orbit, Neptune is sometimes the farthest known planet from the Sun?.

Neptune is never visible with the naked eye. With the use of a telescope it appears as a blue-green disk, similar in appearance to Uranus; the blue-green colour comes from the methane in its atmosphere. Neptune has been visited by only one spacecraft, [Voyager 2]?, which flew by the planet on [August 25]? 1989?.

Orbiting so far from the sun Neptune receives very little heat. Its 'surface' temperature is -218 degrees Celsius (below zero). However, the planet seems to have an internal source of heat. It is thought that this may be leftover heat generated by infalling matter during the planet's birth, now slowly radiating away into space. Neptune's atmosphere has the highest wind speeds in the solar system, up to 2000 km/h, thought to be powered by this flow of internal heat.

Neptune's atmosphere contains :

The internal structure resembles that of Uranus - a rocky core covered by a icy crust, buried deep under its thick atmosphere. The first two thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is a mixture of heated gases comprised of hydrogen, helium, water and methane. Like Uranus, and unlike the uniform composition of Jupiter? and Saturn?, Neptune's internal structure is thought to consist of distinct layers. Like Uranus, Neptune's [magnetic field]? is strongly tilted relative to its rotational axis at 47° and offset at least 0.55 radii (about 13,500 kilometers) from the planet's physical center. Comparing the magnetic fields of the two planets, scientists think the extreme orientation may be characteristic of flows in the interior of the planet and not the result of Uranus' sideways orientation.

Neptune has a faint [planetary ring]? system of unknown compostion. The rings have a peculiar "clumpy" structure, the cause of which is not currently known but which may involve gravitational interaction with small moons in orbit near them. Evidence that the rings are incomplete first arose in the mid-1980s?, when stellar occultation experiments were found to occasionally show an extra "blink" just before or after the planet occulted the star. Images by [Voyager 2]? in 1989? settled the issue, when the ring system was found to contain several faint rings, the outermost of which, Adams, contains three prominent arcs now named Liberty, Equality and Fraternity. The existence of arcs is very difficult to understand because the laws of motion would predict that arcs spread out into a uniform ring over very short timescales. The gravitational effects of Galatea, a moon just inward from the ring, are now believed to confine the arcs. Several other rings were detected by the Voyager cameras. In addition to the narrow Adams Ring 63,000 km from the center of Neptune, the Leverrier Ring is at 53,000 km and the broader, fainter Galle Ring is at 42,000 km. A faint outward extension to the Leverrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km.

Data for Neptune:

Neptune has eight known moons.

Neptune's natural satellites
NameOrbital radius (km)Diameter (km) Mass (kg)
Naiad?48,20058Unknown
Thalassa?50,00080Unknown
Despina?52,600148Unknown
Galatea?62,000158Unknown
Larissa?73,600193 (208 x 178)Unknown
Proteus?117,600418 (436 x 416 x 402)Unknown
Triton?354,76027002.14×1022
Nereid?5,513,400340Unknown

[Solar system]?:
Sun? - Mercury? - Venus? - Earth? - Mars? - Asteroid?s - Jupiter? - Saturn? - Uranus? - Neptune - Pluto? - Comet?s


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Last edited March 2, 2002 5:00 pm (diff)
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