Neptune (planet)

Physical characteristics

Internal composition

The internal composition of Neptune would be similar to that of Uranus. It most probably has a solid core of Silicate S and Fer of about the mass of the Ground. Above this core, there still following the example Uranus, Neptune would have a rather uniform composition (rocks in fusion, ices, 15% of Hydrogène and a little Hélium) and not a structure “in layers” like Jupiter and Saturn.

Atmosphere

The atmosphere of Neptune, thick of more than 8000 km, is made up mainly of Dihydrogène () for 85%, of helium (He) for 13% and methane () for 2%. Traces of Ammonia (), ethane () and Acétylène () were also detected.

The blue color of Neptune comes mainly from the methane which absorbs the light in the wavelengths of the red. However, another compound gives to the clouds of Neptune their characteristic blue color, but it was not identified yet.

Neptune, like the other gas giants, has a wind system made up by fast winds confined in bands parallel at the equator and immense storms and vortex. The winds of Neptune are fastest of the solar system and reach 2000 km/h.

At the time it passage To travel 2 in 1989, the most distinctive mark of planet was the “Grande dark spot” which presented about half of the size of the “Grande red spot Jupiter”. The winds blew there towards the west to 300 m/s (1080 km/h). However, this spot had disappeared when Neptune was observed by the Space telescope Hubble in 1994. Other dark spots at other places were detected since, which indicates that the atmosphere of Neptune changes quickly.

Planetary rings

Magnetic field

The Magnetic field of Neptune, like that of Uranus, is very tilted compared to the axis of planet. It tilted of 47° and is shifted physical center of almost 13.500 km (half of the ray). It is thought that this orientation would come from internal currents to planet.

The moons of Neptune

detailed Article: Natural satellite of Neptune .

Neptune has at least 13 natural satellite of which most important is Triton, discovered by William Lassell 17 days only after the discovery of Neptune.

The negative periods of revolution indicate that the orbit of the moon is retrograde.

Trojan Asteroids of Neptune

Like Jupiter and Mars, Neptune has Trojan asteroids, sharing its orbit around the Sun. Four were confirmed to date (April 2006):

All occupy the Point Lagrange L (precede Neptune by 60°).

Discovered of Neptune

Neptune is not visible with the naked eye and like Uranus, it was discovered only after the invention of the Télescope. However, this discovery dissociates that of another planets: it was made only by the calculation starting from the trajectory and of the characteristics of Uranus. The telescope will be used only for the confirmation of the discovery.

Several astronomers missed making the discovery by the traditional means (observation with the telescope). The astronomical drawings of Galileo show that it observed Neptune the December 28th 1612 whereas it looked at Jupiter. The planet is then indexed like simple a star of magnitude 8. He again notices it in the sky one month later, the January 28th 1613, and even notes that it moved compared to a close star. It cannot thus be a star, but Galileo does not draw any conclusion and will not speak again about it thereafter any more. As he thought that it was about a star, he cannot then be credited with his discovery.

Neptune is also observed by Joseph Jerome Lefrançois de Lalande (1732-1807) the May 10th 1795 and by John Herschel, wire of William Herschel (which discovered Uranus), without anything to note of private individual. The planet seeming to escape the astronomers, the discovery will total two mathematicians.

Already in 1788, the planet Uranus recently discovered, did not seem to conform to the model of orbit which the astronomers had predicted. The more time passed and the more the error between the announced position of the star and that raised increased. The movement of Uranus could be predicted for observations old, or recent, but not for both at the same time. Jean-Baptiste Delambre tried to explain the anomalies by adding the gravitational influence of Jupiter and Saturn in its calculations. Its tables were more precise, but still did not allow to envisage the movement of planet on a long run. In 1821, the French astronomer Alexis Bouvard published new tables. It used 17 observations spread out over the 40 years which were passed since its discovery to try, in vain, to explain the orbit of Uranus.

At a meeting of the British Association for the Advancement off Science, George Biddell Airy reported that the tables of Bouvard were erroneous of more than one half minute of arc. This worrying variation was absolutely to be solved. Alexis Claude Clairaut was the first to put forth the assumption of another planet, still unknown, and which could affect the movements of Uranus. Clairaut compared Uranus with the Halley's Comet, subjected to completely unknown forces the such gravitational interaction of other comets, or even of another planets. Airy, which was rather preserving, did not appreciate these new planets so much and preferred its own theory as what the law of Gravitation would lose its validity as one moves away from the Sun. However, as of 1838, the majority of the astronomers were of agreement on the existence of a new transuranic planet to explain the disturbances of the movement of Uranus.

Student with Cambridge, John Couch Adams fell the June 26th 1841 on the report/ratio from Airy concerning the problem from the orbit from Uranus and was interested by the question. Not being able to concentrate itself on the problem immediately, it foot-note on a bit of paper as a crib in order to take it again once its finished studies. In 1843, Adams was put at work. It was based on the law of Titius-Bode to obtain a first approximation of the distance from this new planet to the Sun. Insofar as the majority of planets had an orbit slightly eccentric, it also supposed that its orbit was circular, in order to simplify calculations. It completes its work later two years while having determined the position of Neptune with an error of less than two degrees. It any more but did not fail to him to confirm them by observation. Turning to James Challis, director of the observatory of Cambridge, this one return it to the royal astronomer Sir George Biddell Airy. Airy hardly appreciated this work and seemed to do everything to avoid Adams. This last succeeds in transmitting its results by mail to him the October 21st 1845, and obtained an answer the 5 of the next month. Airy seemed in its answer in complete shift with work of Adams and asked him some uninteresting questions, more in report/ratio about its own theory of the movement of Uranus that on calculations of Adams. Nauseated by the behavior of Airy, Adams will answer him afterwards only one year.

At the same time in France, François Arago, director of the observatory of Paris, encourage the mathematician Urbain the Glassmaker, specialized in celestial mechanics, to determine the characteristics of this eighth planet whose gravitational influence was felt on the trajectory of Uranus. The Glassmaker worked then on comets of short period. He begins his work on Uranus in 1845, being unaware of those of Adams completely, and publishes his first results the November 10th 1845 in Premier Report on the Theory of Uranus , then in Recherche on the Movements of Uranus on June 1st 1846.

Airy, noticing work of the French astronomer, does it parallel with those of Adams and comes into contact with the Glassmaker. This one requires of him in its turn to carry out research of planet using calculations which it has just published, but Airy refuses. Finally, under the pressure of George Peacock, Airy requires of Challis the July 12th 1846 to begin the research of the new star to the telescope. Adams, informed by the director of Cambridge, provides new coordinates to Challis by specifying that the object would be magnitude 9, but Airy not wanting to accept that a planet can be discovered starting from mathematical calculations, it proposed in Challis to observe a broad portion of the sky and until magnitude 11. This method required of Challis much more time of observation. It began its research on August 1st 1846.

The Glassmaker communicates his final results with the Academy of Science the August 31st 1846. In front of the little of enthusiasm of the French astronomers, it decides to then call upon one of its knowledge: the Prussian astronomer Johann Gottfried Galle of the observatory of Berlin. Galle receives the position of Neptune by mail the September 23rd 1846. The evening even, it points its telescope of 23 cm towards the place indicated and passes to the fine comb all stars of the area, while its assistant Heinrich Louis d' Arrest checked if the star observed were indexed on the recent charts stellar of Bremiker. About midnight, Galle found Neptune, with less than one degree of the calculated site. He waited a few hours to check if the star moved well, before confirming that it was indeed required planet.

On the other side of the channel, disappointment is large. Challis learns the discovery by reading the Times . By re-examining its notes, he even discovers that he had observed Neptune twice since August 1st. A sharp polemic follows until in the press. The British bring out papers of exclaiming Adams that the discovery their cost. On their side, the French refute by recalling that only an official publication can validate the discovery, and refuse firm footing that the name of Adams appears beside that of the Glassmaker in the books of history. In June 1847, Adams and the Glassmaker met for the first time at British Association for the Advancement off Science and maintained since a friendly relation.

During new calculations on the orbital characteristics of Neptune, one realized that those of the Glassmaker and Adams were false, although both announced the position of planet not far from its real position. The first had determined a radius of 36,154 ua and an eccentricity of 0,107 while the second had found a radius of 37,25 ua. The real ray of the orbit of Neptune is 30,1 ua and its eccentricity lower than 0,009. In addition, of the historians found elements which tend to show that the solutions of Adams did not converge but varied by more than 35 degrees of longitude.

With one orbital period of almost 165 years, Neptune will turn over only in 2011 to the point where Galle had observed it.

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