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. Like Uranus, and unlike the uniform composition of Jupiter and Saturn, Neptune's internal structure is thought to consist of distinct layers. Neptune's magnetic field is strongly tilted relative to its rotational axis, and is thought to be generated by the movement of conductive liquid water in its inner layers.
Neptune has a faint 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.
Data for Neptune:
Neptune has eight known moons.
| Name of the satellite | Mean Distance from parent Planet (km) | Diameter of satellite (km) | mass (kg) |
|---|---|---|---|
| Naiad | 48,000 | 58 | ? |
| Thalassa | 50,000 | 80 | ? |
| Despina | 53,000 | 148 | ? |
| Galatea | 62,000 | 158 | ? |
| Larissa | 74,000 | 192 | ? |
| Proteus | 118,000 | 418 | ? |
| Triton | 355,000 | 2700 | 2.14e22 |
| Nereid | 5,509,000 | 340 | ? |
Solar system:
Sun - Mercury - Venus - Earth - Mars - Asteroids - Jupiter - Saturn - Uranus - Neptune - Pluto - Comets
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