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Γραμμή 1:
{{Πληροφορίες πλανήτη
|bgcolour = #a0ffa0
|όνομα = Άρης
|Σύμβολο = [[Αρχείο:Mars symbol.svg|25px|Αστρονομικό σύμβολο του Άρη]]
|Εικόνα = [[Αρχείο:Water ice clouds hanging above Tharsis PIA02653.jpg|250px]]
|λεζάντα =
|Ανακαλύφθηκε_από =
|Ημερομηνία_ανακάλυψης =
|Μέθοδος_ανακάλυψης =
|Προφορά =
|Ονομάστηκε_από =
|Άλλα_ονόματα = Κόκκινος πλανήτης, Πυρόεις από τους αρχαίους Έλληνες.
|Ιδιότητες_και_Επίθετα =
|Αστρονομική_Εποχή =
|Αφήλιο = 249.209.300 [[Χιλιόμετρο|χλμ.]],<ref name=horizons>{{cite web|last=Yeomans|first=Donald K.|date=2006-07-13|url=http://ssd.jpl.nasa.gov/?horizons|title=Σύστημα HORIZONS|publisher=NASA JPL|accessdate=2007-08-08}}</ref><br /> (1,665861 [[Αστρονομική μονάδα|AU]])
|Περιήλιο = 206.669.000 χλμ.,<ref name=horizons/><br /> (1,381497 AU)
|Περίαψις =
|Ημιάξονας_τροχιάς = 227.939.100 χλμ.,<ref name=horizons/><br /> (1,523679 AU)
|Μέση_ακτίνα_τροχιάς =
|Περιφέρεια_τροχιάς =
|Εκκεντρότητα = 0,093315<ref name=horizons/>
|Περίοδος_περιφοράς = 686,971 [[Ημέρα|ημέρες]],<ref name=horizons/><br /> (1,8808 [[Έτος|έτη]])
|Συνοδική_περίοδος_περιφοράς = 779,96 ημέρες,<ref name=horizons/><br /> (2,135 έτη)
|Μέγιστη_τροχιακή_ταχύτητα =
|Μέση_τροχιακή_ταχύτητα = 24,077 χλμ./δευτ.,<ref name=horizons/><br /> 86.677,2 χλμ./ώρα
|Ελάχιστη_τροχιακή_ταχύτητα =
|Μέση_ανωμαλία = 19,3564°<ref name=horizons/>
|Κλίση_τροχιάς = 1,85061°(ως προς την [[Εκλειπτική]]),<ref name=horizons/><br /> 5,65°(ως προς τον [[Ήλιος|Ηλιακό]] ισημερινό)
|Γωνιακή_απόσταση =
|Μήκος του ανερχόμενου σημείου = 49,562°<ref name=horizons/>
|Όρισμα του περιηλίου = 286,537°<ref name=horizons/>
|Δορυφόροι = 2 φυσικοί ([[Φόβος (δορυφόρος)|Φόβος]], [[Δείμος (δορυφόρος)|Δείμος]])
|Διαστάσεις =
|Μέση_ακτίνα =
|Ακτίνα_ισημερινού = 3.396,2 ± 0,1 χλμ.<ref name=Seidelmann2007>{{cite journal|last=Seidelmann|first=P. Kenneth|coauthors=Archinal, B. A.; A'hearn, M. F.; ''et al''.|title=Έκθεση της Ομάδα Εργασίας IAU / IAG για χαρτογραφικές συντεταγμένες και ταχύτητες περιστροφής στοιχεία: 2006|journal=Ουράνια Μηχανική και Δυναμική Αστρονομία|volume=98|issue=3|pages=155–180|year=2007|doi=10.1007/s10569-007-9072-y|bibcode=2007CeMDA..98..155S}}</ref>
|Ακτίνα_πόλου = 3.376,2 ± 0,1 χλμ.<ref name=Seidelmann2007/>
|Πλάτυνση = 0,00589 ± 0,00015
|Περιφέρεια_ισημερινού = 21.340 χλμ.
|Πολική_περιφέρεια = 21.210 χλμ.
|Εμβαδόν_επιφάνειας = 144.798.500 [[Τετραγωνικό μέτρο|χλμ.<sup>2</sup>]]
|Όγκος = 1,6318·10<sup>11</sup> [[Κυβικό μέτρο|χλμ.<sup>3</sup>]]<ref name=lodders1998>{{cite book|author=Lodders, Katharina; Fegley, Bruce|year=1998|title=Το εγχειρίδιο του πλανητικού επιστήμονα|page=190|publisher=Oxford University Press US|isbn=0-19-511694-1}}</ref>
|Μάζα = 6,4185·10<sup>23</sup> [[Χιλιόγραμμο|χλγρ.]]<ref name=lodders1998/>
|Μέση_πυκνότητα = 3,9335 ± 0,0004 γρμ./εκ.<sup>3</sup><ref name=lodders1998/>
|Βαρύτητα_επιφάνειας = 3,711 μ./δευτ.<sup>2</sup>,<ref name=lodders1998/><br /> 0,376 [[Επιτάχυνση της βαρύτητας|g]]
|Ταχύτητα_διαφυγής = 5,027 χλμ./δευτ.
|Περίοδος_περιστροφής =
|Αστρονομική_περίοδος_περιστροφής = 1,025957 ημέρες,<br /> 24,6229 ώρες.<ref name=lodders1998/>
|Tαχύτητα_περιστροφής = 868,22 χλμ./ώρα,<br /> (241,17 μ./δευτ.)
|Κλίση_άξονα = 25,19°
|Απόκλιση =
|Λευκαύγεια = 0,170
|Θερμοκρασία_Επιφάνειας = 186 [[Κλίμακα Κέλβιν|K]] - 293 K,<br /> (-87 [[Κλίμακα Κελσίου|°C]] - 20&nbsp;°C)
|Φαινόμενο_μέγεθος = +1,6 έως −3,0
|Γωνιακή_διάμετρος = 3,5 - 25,1"<ref name=Factsheet>{{cite web|author=Williams, David R.|title=Πίνακας δεδομένων της Γης|publisher=NASA|date=September 1, 2004|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html|accessdate=2006-06-24}}</ref>
|Απόλυτο_μέγεθος =
|Ατμοσφαιρική_πίεση_επιφανείας = 636 [[Νιούτον (μονάδα μέτρησης)|Νιούτον]]/μ.<sup>2</sup><ref name=Factsheet/>
|Ατμοσφαιρική_σύσταση = 95,32% [[Διοξείδιο του άνθρακα]]<ref name=Factsheet/><br /> 2,70% [[Άζωτο]]<br /> 1,60% [[Αργό]]<br /> 0,13% [[Οξυγόνο]]<br /> 0,08% [[Μονοξείδιο του άνθρακα]]
}}
 
<table border="1" cellspacing="0" cellpadding="2" align="right" style="width: 25em">
<caption><big>'''Ποσειδώνας'''</big> [[Αρχείο:Neptune symbol.ant.png|30px]] </caption>
Γραμμή 176 ⟶ 117 :
</table>
 
Ο '''Ποσειδώνας''' είναι ο όγδοος, κατά σειρά απόστασης από τον [[ήλιος|ήλιο]], [[πλανήτης]] του [[Ηλιακό Σύστημα|Ηλιακού Συστήματος]]. Δεν είναι ορατός με γυμνό μάτι, ενώ αν παρατηρηθεί με ισχυρό τηλεσκόπιο μοιάζει με πράσινο δίσκο. Στην [[αστρονομία]] συμβολίζεται με την τρίαινα [[Αρχείο:Neptune symbol.ant.png|20px|♀]]
Ο '''Ποσειδώνας''' (διεθνώς:''Neptune'') είναι το όγδοος και μακρινότερος [[πλανήτης]] από τον [[Ήλιος|Ήλιο]] στο [[Ηλιακό Σύστημα]]. Είναι ο τέταρτος μεγαλύτερος πλανήτης σε διάμετρο και τρίτος μεγαλύτερος σε μάζα. Ανάμεσα στους [[gaseous planets]] στο Ηλικαό Σύστημα, ο Ποσειδώνας είναι ο πυκνότερος. Ο Ποσειδώνας έχει 17 φορές τη μάζα της [[Γη]]ς και είναι ελαφρά μεγαλύτερης μάζας από τον σχεδόν δίδυμό του [[Ουρανός (πλανήτης)|Ουρανό]], ο οποίος έχει 15 φορές τη μάζα της Γης αλλά δεν είναι τόσο πυκνός.<ref group=lower-alpha name="mass"/> Ο Ποσειδώνας περιστρέφεται γύρω από τον Ήλιο με μέση απόσταση 30,1 [[αστρονομική μονάδα|αστρονομικές μονάδες]]. Έχει πάρει το όνομά του από τον [[Νεπτούνους|Ρωμαϊκό θεό της θάλασσας]], το [[αστρονομικό σύμβολο]] του είναι ♆<!--[[File:Neptune symbol.svg|20px|Astronomical symbol for Neptune.]]-->, a stylised version of the god Neptune's [[trident]].
 
Ανακαλυμμένος στις 23 Σεπτεμβρίου 1846, ο Ποσειδώνας ήταν ο πρώτος πλανήτης που βρέθηκε σύμφωνα με μαθηματική πρόβλεψη και όχι από εμπειρικές παρατηρήσεις. Οι απροσδόκητες μεταβολές στην τροχιά του [[ουρανός (πλανήτης)|Ουρανού]] οδήγησε τον Αλέξ Μπουβάρντ να συμπεράνει ότι η τροχιά του υπόκειται σε βαρυτική διαταραχή από έναν άγνωστο πλανήτη. Ο Ποσειδώνας στη συνέχεια παρατηρήθηκε από τον [[Γιόχαν Γκότφριντ Γκάλε]] σε απόσταση μικρότερη από μία μοίρα από τη θέση που προέβλεψε ο [[Ουρμπέν Λεβεριέ]], και το μεγαλύτερο φεγγάρι του, ο [[τρίτωνας (δορυφόρος)|Τρίτωνας]], ανακαλύφθηκε λίγο αργότερα, αν και κανένα των υπόλοιπων 12 δορυφόρων του πλανήτη δεν ανιχνεύτηκε τηλεσκοπικά μέχρι τον 20ο αιώνα. Τον Ποσειδώνα έχει επισκεφθεί ένα μόνο διαστημόπλοιο, το [[Βόγιατζερ 2]], το οποίο πέταξε από τον πλανήτη στις 25 Αυγούστου, 1989.
Ο Ποσειδώνας ήταν ο πρώτος πλανήτης που ανακαλύφθηκε από μαθηματική πρόβλεψη παρά από [[εμπειρική παρατήρηση]]. Μη αναμενόμενες αλλαγές στην περιστροφή του [[Ουρανός (πλανήτης)|Ουρανού]] οδήγησαν τον [[Αλέξις Μπουβάρ]] να συμπεράνει ότιto deduce that its orbit was subject to [[gravitation]]al [[perturbation (astronomy)|perturbation]] by an unknown planet.
 
Ο Ποσειδώνας έχει παρόμοια σύνθεση με τον Ουρανό, ενώ και οι δύο έχουν συνθέσεις που διαφέρουν από εκείνες των μεγαλύτερων γιγάντων αερίων, [[Δίας (πλανήτης)|Δία]] και [[Κρόνος (πλανήτης)|Κρόνου]]. Η ατμόσφαιρα του Ποσειδώνα, ενώ είναι παρόμοια με του Δία και του Κρόνου στο ότι αποτελείται κυρίως από [[υδρογόνο]] και [[ήλιο]], μαζί με τα ίχνη [[υδρογονάνθρακας|υδρογονανθράκων]] και, ενδεχομένως, του [[άζωτο|αζώτου]], περιέχει μεγαλύτερο ποσοστό των «πάγων», όπως [[νερό]], [[αμμωνία]] και [[μεθάνιο]]. Οι αστρονόμοι κατηγοριοποιούν ενίοτε τους Ουρανό και Ποσειδώνα ως «γίγαντες πάγου», προκειμένου να τονίσουν τις διακρίσεις αυτές. Το εσωτερικό του Ποσειδώνα, όπως και του Ουρανού, αποτελείται κυρίως από πάγο και βράχους.<ref name=Podolak1995>{{cite journal
<!--
|last=Podolak|first=M.
Neptune was subsequently observed on 23 September 1846<ref name="Hamilton"/> by [[Johann Galle]] within a [[Degree (angle)|degree]] of the position predicted by [[Urbain Le Verrier]], and its largest moon, [[Triton (moon)|Triton]], was discovered shortly thereafter, though none of the planet's remaining 13 [[Moons of Neptune|moons]] were located telescopically until the 20th century. Neptune has been visited by one spacecraft, ''[[Voyager 2]]'', which flew by the planet on 25 August 1989.
|coauthors=Weizman, A.; Marley, M.
 
|title=Comparative models of Uranus and Neptune
Neptune is similar in composition to [[Uranus]], and both have compositions which differ from those of the larger [[gas giant]]s, [[Jupiter]], and [[Saturn]]. Neptune's atmosphere, while similar to Jupiter's and Saturn's in that it is composed primarily of [[hydrogen]] and [[helium]], along with traces of [[hydrocarbon]]s and possibly [[nitrogen]], contains a higher proportion of "ices" such as water, [[ammonia]], and [[methane]]. Astronomers sometimes categorise Uranus and Neptune as "[[ice giant]]s" in order to emphasise these distinctions.<ref name="Lunine 1993"/> The interior of Neptune, like that of Uranus, is primarily composed of ices and rock.<ref name="Podolak Weizman et al. 1995"/> It is possible that the core has a solid surface, but the temperature would be thousands of degrees and the atmospheric pressure crushing.<ref>[http://www.universetoday.com/22070/surface-of-neptune/ Upper Surface of Neptune]. Universetoday.com (2008-12-09). Retrieved on 2013-07-28.</ref> Traces of methane in the outermost regions in part account for the planet's blue appearance.<ref name=bluecolour>
|journal=Planetary and Space Science|volume=43
{{cite web
|issue=12|pages=1517–1522|year=1995
|url=http://adsabs.harvard.edu/abs/1995P%26SS...43.1517P
|doi=10.1016/0032-0633(95)00061-5}}</ref> Ίχνη μεθανίου στις εξώτερες περιοχές του πλανήτη ευθύνονται εν μέρει για την μπλε εμφάνιση του πλανήτη.<ref name=bluecolour>{{cite web
|first=Kirk|last=Munsell
|coauthors=Smith, Harman; Harvey, Samantha
|date=13 November 13, 2007
|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune&Display=OverviewLong
|title=Neptune overview|work=Solar System Exploration
|publisher=NASA|accessdate=2008-02-20}}</ref>
|work=Solar System Exploration
|publisher=NASA
|accessdate=20 February 2008
}}</ref>
 
Σε αντίθεση με τη σχετικά ήρεμη ατμόσφαιρα του Ουρανού, η ατμόσφαιρα του Ποσειδώνα είναι αξιοσημείωτη για τα ενεργά και ορατά καιρικά φαινόμενα της. Όταν το [[Βόγιατζερ 2]] προσέγγισε τον Ποσειδώνα, για παράδειγμα, στο νότιο ημισφαίριο του πλανήτη υπήρχε μία μεγάλη σκοτεινή κηλίδα, συγκρίσιμη με τη Μεγάλη Ερυθρά Κηλίδα στο [[Δίας (πλανήτης)|Δία]]. Αυτές οι καιρικές συνθήκες καθοδηγούνται από τους ισχυρότερους συνεχείς ανέμους κάθε πλανήτη στο ηλιακό μας σύστημα, καθώς καταγράφονται ταχύτητες ανέμου τόσο υψηλές όσο 2.100 χιλιόμετρα ανά ώρα.<ref name="Suomi1991">{{cite journal
In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere is notable for its active and visible weather patterns. For example, at the time of the 1989 ''Voyager 2'' [[planetary flyby|flyby]], the planet's southern hemisphere possessed a [[Great Dark Spot]] comparable to the [[Great Red Spot]] on [[Jupiter]]. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as {{convert|2100|kph|mph}}.<ref name="Suomi1991">
|last=Suomi|first=V. E.
{{cite journal
|coauthors=Limaye, S. S.; Johnson, D. R.|year=1991
|last=Suomi |first=V. E.
|coauthors=Limaye, S. S.; Johnson, D. R.
|year=1991
|title=High Winds of Neptune: A possible mechanism
|journal=[[Science (journal)|Science]]|volume=251
|issue=4996|pages=929–932|publisher=AAAS (USA)
|volume=251
|issue=4996 |pages=929–932
|doi=10.1126/science.251.4996.929
|pmid=17847386
}}</ref> Λόγω της μεγάλης απόστασης από τον Ήλιο, η εξωτερική ατμόσφαιρα του Ποσειδώνα είναι ένα από τα πιο κρύα μέρη στο ηλιακό σύστημα, με τη θερμοκρασία στις κορυφές συννέφων να πλησιάζουν τους -218&nbsp;°C (55 K). Ωστόσο, η θερμοκρασία στο κέντρο του πλανήτη είναι περίπου 5.400 Κ (5.000&nbsp;°C).<ref name="nettelmann">{{cite web
|bibcode=1991Sci...251..929S
|last=Nettelmann|first=N.
}}</ref> Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching {{convert|55|K|C|0|lk=on}}<!--note that the template is no good, abbr=off has no effect-->. Temperatures at the planet's centre are approximately {{convert|5400|K|C|-3}}.<ref name=hubbard/><ref name="nettelmann"/> Neptune has a faint and fragmented [[planetary ring|ring system]] (labeled 'arcs'), which may have been detected during the 1960s but was only indisputably confirmed in 1989 by ''Voyager 2''.<ref name=ring1/>
|coauthors=French, M.; Holst, B.; Redmer, R.|url=https://www.gsi.de/informationen/wti/library/plasma2006/PAPERS/TT-11.pdf
 
|format=PDF
==History==
|title=Interior Models of Jupiter, Saturn and Neptune
 
|publisher=University of Rostock|accessdate=2008-02-25
===Discovery===
}}</ref> Ο Ποσειδώνας έχει ένα αχνό και κατακερματισμένο σύστημα δακτυλίων, οι οποίοι είχαν ανιχνευτεί κατά τη διάρκεια της δεκαετίας του 1960, όμως, ήταν αναμφισβήτητα η ύπαρξή τους επιβεβαιώθηκε μόνο το 1989 από το Voyager 2.<ref name=ring1>{{cite news
{{main|Discovery of Neptune}}
|last=Wilford|first=John N.|date=June 10, 1982
[[Galileo Galilei|Galileo's]] drawings show that he first observed Neptune on 28 December 1612, and again on 27 January 1613. On both occasions, Galileo mistook Neptune for a [[fixed star]] when it appeared very close—in [[Conjunction (astronomy and astrology)|conjunction]]—to Jupiter in the [[night sky]];<ref>
|title=Data Shows 2 Rings Circling Neptune
{{cite book
|publisher=The New York Times
|first=Alan|last=Hirschfeld
|url=http://query.nytimes.com/gst/fullpage.html?sec=technology&res=950DE3D71F38F933A25755C0A964948260&n=Top/News/Science/Topics/Space
|title=Parallax: The Race to Measure the Cosmos|year=2001
|accessdate=2008-02-29}}</ref>
|publisher=Henry Holt
|location=New York, New York
| isbn = 978-0-8050-7133-7
}}</ref> hence, he is not credited with Neptune's discovery. During the period of his first observation in December 1612, Neptune was stationary in the sky because it had just turned [[Apparent retrograde motion|retrograde]] that very day. This apparent backward motion is created when the orbit of the Earth takes it past an outer planet. Since Neptune was only beginning its yearly retrograde cycle, the motion of the planet was far too slight to be detected with Galileo's small [[telescope]].<ref>
{{cite book
|first=Mark |last=Littmann
|coauthors=Standish, E. M.
|title=Planets Beyond: Discovering the Outer Solar System
|year=2004
|publisher=Courier Dover Publications
| isbn = 978-0-486-43602-9
}}</ref> In July 2009, [[University of Melbourne]] physicist David Jamieson announced new evidence suggesting that Galileo was at least aware that the star he had observed had moved relative to the [[fixed stars]].<ref>
{{cite web
|title=Galileo discovered Neptune, new theory claims
|first=Robert Roy |last=Britt
|year=2009
|publisher=MSNBC News
|accessdate=10 July 2009
|url=http://www.msnbc.msn.com/id/31835303
}}</ref>
 
In 1821, [[Alexis Bouvard]] published astronomical tables of the [[orbit]] of Neptune's neighbour Uranus.<ref>
{{cite book
|first=A. |last=Bouvard
|year=1821
|title=Tables astronomiques publiées par le Bureau des Longitudes de France
|publisher=Bachelier
|location=Paris
}}</ref> Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize that an unknown body was [[Perturbation (astronomy)|perturbing]] the orbit through [[gravitation]]al interaction.<ref name=MNRAS7 /> In 1843, [[John Couch Adams]] began work on the orbit of Uranus using the data he had. Via [[Cambridge Observatory]] director [[James Challis]], he requested extra data from Sir [[George Biddell Airy|George Airy]], the [[Astronomer Royal]], who supplied it in February 1844. Adams continued to work in 1845–46 and produced several different estimates of a new planet.<ref>
{{cite web
|first=John J. |last=O'Connor
|coauthors=Robertson, Edmund F.
|year=2006
|url=http://www-groups.dcs.st-and.ac.uk/~history/Extras/Adams_Neptune.html
|title=John Couch Adams' account of the discovery of Neptune
|publisher=University of St Andrews
|accessdate=18 February 2008}}
</ref><ref>
{{cite journal
|first=J. C. |last=Adams
|bibcode=1846MNRAS...7..149A
|title=Explanation of the observed irregularities in the motion of Uranus, on the hypothesis of disturbance by a more distant planet
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=7 |page=149 |date=13 November 1846
}}</ref>
 
[[File:Urbain Le Verrier.jpg|thumb|upright|left||[[Urbain Le Verrier]]]]
 
In 1845–46, [[Urbain Le Verrier]], independently of Adams, developed his own calculations but also experienced difficulties in stimulating any enthusiasm in his compatriots. In June 1846, upon seeing Le Verrier's first published estimate of the planet's longitude and its similarity to Adams's estimate, Airy persuaded Challis to search for the planet. Challis vainly scoured the sky throughout August and September.<ref name=MNRAS7>
{{cite journal
|first=G. B. |last=Airy
|bibcode=1846MNRAS...7..121A
|title=Account of some circumstances historically connected with the discovery of the planet exterior to Uranus
|journal=Monthly Notices of the Royal Astronomical Society
|volume=7 |pages=121–144 |date=13 November 1846
|doi=10.1002/asna.18470251002
}}</ref><ref>
{{cite journal
|first=Rev. J. |last=Challis
|bibcode=1846MNRAS...7..145C
|title=Account of observations at the Cambridge observatory for detecting the planet exterior to Uranus
|journal=Monthly Notices of the Royal Astronomical Society
|volume=7 |pages=145–149
|date=13 November 1846
}}</ref>
 
Meantime, Le Verrier by letter urged [[Berlin Observatory]] astronomer [[Johann Gottfried Galle]] to search with the observatory's [[refractor]]. [[Heinrich Louis d'Arrest|Heinrich d'Arrest]], a student at the observatory, suggested to Galle that they could compare a recently drawn chart of the sky in the region of Le Verrier's predicted location with the current sky to seek the displacement characteristic of a [[planet]], as opposed to a fixed star. The very evening of the day of receipt of Le Verrier's letter on 23 September 1846, Neptune was discovered within 1° of where Le Verrier had predicted it to be, and about 12° from Adams' prediction. Challis later realised that he had observed the planet twice in August (Neptune had been observed on 8 and 12 August, but because Challis lacked an up-to-date star-map it was not recognised as a planet), failing to identify it owing to his casual approach to the work.<ref name=MNRAS7/><ref>
{{cite journal
|first=J. G.|last=Galle
|bibcode=1846MNRAS...7..153G
|title=Account of the discovery of the planet of Le Verrier at Berlin
|journal=Monthly Notices of the Royal Astronomical Society
|volume=7 |page=153
|date=13 November 1846
}}</ref>
 
In the wake of the discovery, there was much nationalistic rivalry between the French and the British over who had priority and deserved credit for the discovery. Eventually an international consensus emerged that both Le Verrier and Adams jointly deserved credit. Since 1966 [[Dennis Rawlins]] has questioned the credibility of Adams's claim to co-discovery and the issue was re-evaluated by historians with the return in 1998 of the "Neptune papers" (historical documents) to the [[Royal Observatory, Greenwich]].<ref name="Neptdisc">
{{cite web
|url=http://www.ucl.ac.uk/sts/nk/neptune/index.htm
|title=Neptune's Discovery. The British Case for Co-Prediction.
|accessdate=19 March 2007
|first=Nick |last=Kollerstrom
|year=2001
|publisher=University College London
|archiveurl=http://web.archive.org/web/20051111190351/http://www.ucl.ac.uk/sts/nk/neptune/
|archivedate=11 November 2005
}}</ref> After reviewing the documents, they suggest that "Adams does not deserve equal credit with Le Verrier for the discovery of Neptune. That credit belongs only to the person who succeeded both in predicting the planet's place and in convincing astronomers to search for it."<ref>
{{cite journal
|author= William Sheehan, Nicholas Kollerstrom, Craig B. Waff
|month=December 2004
|url=http://www.scientificamerican.com/article.cfm?id=the-case-of-the-pilfered
|title=The Case of the Pilfered Planet&nbsp;– Did the British steal Neptune?
|work=Scientific American
|accessdate=20 January 2011
}}</ref>
 
===Naming===
Shortly after its discovery, Neptune was referred to simply as "the planet exterior to Uranus" or as "Le Verrier's planet". The first suggestion for a name came from Galle, who proposed the name ''[[Janus (mythology)|Janus]]''. In England, Challis put forward the name ''[[Oceanus]]''.<ref>[[#Moore|Moore]] (2000):206</ref>
 
Claiming the right to name his discovery, Le Verrier quickly proposed the name ''Neptune'' for this new planet, while falsely stating that this had been officially approved by the French [[Bureau des Longitudes]].<ref>{{cite book
| last = Littmann|first=Mark|year=2004
| title = Planets Beyond, Exploring the Outer Solar System
| publisher = Courier Dover Publications
| isbn = 978-0-486-43602-9|page=50}}</ref> In October, he sought to name the planet ''Le Verrier'', after himself, and he had loyal support in this from the observatory director, [[François Arago]]. This suggestion met with stiff resistance outside France.<ref>{{cite book|ref=Baum
| last = Baum|first=Richard|coauthors=Sheehan, William
| year = 2003
| title = In Search of Planet Vulcan: The Ghost in Newton's Clockwork Universe
| publisher = Basic Books|isbn = 978-0-7382-0889-3|pages=109–110}}</ref> French almanacs quickly reintroduced the name ''Herschel'' for ''Uranus'', after that planet's discoverer Sir [[William Herschel]], and ''Leverrier'' for the new planet.<ref>
{{cite journal
|first=Owen |last=Gingerich
|title=The Naming of Uranus and Neptune
|journal=Astronomical Society of the Pacific Leaflets
|year=1958 |volume=8 |pages=9–15
|bibcode=1958ASPL....8....9G
}}</ref>
 
[[Friedrich Georg Wilhelm von Struve|Struve]]<!--- (1793–1864), or maybe his son Otto Wilhelm von Struve (1819–1905). (Having looked at the original text it seems like it's most likely the elder of the struve's, but the text is ambigious) ---> came out in favour of the name ''Neptune'' on 29 December 1846, to the [[Russian Academy of Sciences|Saint Petersburg Academy of Sciences]].<ref>{{cite journal
|title=Second report of proceedings in the Cambridge Observatory relating to the new Planet (Neptune)
|year=1847
|journal=Astronomische Nachrichten
|volume=25 |issue=21 |page=309
|last=Hind|first=J. R.
|doi=10.1002/asna.18470252102
|url=http://onlinelibrary.wiley.com/doi/10.1002/asna.18470252102/abstract}}</ref> Soon ''Neptune'' became the internationally accepted name. In [[Roman mythology]], [[Neptune (mythology)|Neptune]] was the god of the sea, identified with the Greek [[Poseidon]]. The demand for a mythological name seemed to be in keeping with the nomenclature of the other planets, all of which, except for Earth, were named for deities in [[Greek mythology|Greek]] and [[Roman mythology]].<ref name=USGS>
{{cite web
|first=Jennifer |last=Blue
|date=17 December 2008
|url=http://planetarynames.wr.usgs.gov/Page/Planets
|title=Planet and Satellite Names and Discoverers
|publisher=USGS
|accessdate=18 February 2008
}}</ref>
 
Most languages today, even in countries that have no direct link to Greco-Roman culture, use some variant of the name "Neptune" for the planet; in Chinese, Japanese and [[Korean language|Korean]], the planet's name was literally translated as "sea king star" ({{lang|zh|海王星}}), since Neptune was the god of the sea.<ref>{{cite web|title=Planetary linguistics|publisher=nineplanets.org|url=http://nineplanets.org/days.html|accessdate=8 April 2010}}</ref> In modern [[Greek language|Greek]], though, the planet is called ''Poseidon'' (Ποσειδώνας: ''Poseidonas''), the Greek counterpart to Neptune.<ref>{{cite web|url=http://www.greek-names.info/greek-names-of-the-planets/|title=Greek Names of the Planets|accessdate=2012-07-14|quote=Neptune or ''Poseidon'' as is its Greek name, was the God of the Seas. It is the eight planet from the sun...}} See also the [[:el:Ποσειδώνας (πλανήτης)|Greek article about the planet]].</ref>
 
===Status= Γενικά ==
[[Αρχείο:Urbain Le Verrier.jpg|thumb|upright|left||Ο Ουρμπέν Λεβεριέ]]
From its discovery in 1846 until the subsequent [[discovery of Pluto|discovery]] of [[Pluto]] in 1930, Neptune was the farthest known planet. Upon Pluto's discovery Neptune became the penultimate planet, save for a 20-year period between 1979 and 1999 when Pluto's elliptical orbit brought it closer to the Sun than Neptune.<ref>{{cite news|title=Jan. 21, 1979: Neptune Moves Outside Pluto's Wacky Orbit|work=Wired|url=http://www.wired.com/science/discoveries/news/2008/01/dayintech_0121
Ανακαλύφθηκε θεωρητικά το [[1843]], πριν παρατηρηθεί με τηλεσκόπιο, λόγω των [[βαρύτητα|βαρυτικών του επιδράσεων]] ([[πάρελξη|παρέλξεις]]) που ασκούσε στον [[Ουρανός (πλανήτης)|Ουρανό]]. Ο Γάλλος μαθηματικός αστρονόμος [[Υρμπαίν Λεβεριέ]] (Urbain Leverrier, 1811-1877) του αστεροσκοπείου των Παρισίων, υπολόγισε θεωρητικά και υπέδειξε την ακριβή θέση στην οποία έπρεπε να βρίσκεται ένας άγνωστος πλανήτης, όπου και πράγματι βρέθηκε (παρατηρήθηκε) και καταγράφηκε στις [[23 Σεπτεμβρίου]] του [[1846]] από τον Γερμανό αστρονόμο [[Γιόχαν Γκότφριντ Γκάλε]] (Johan Galle) του αστεροσκοπείου του Βερολίνου.
|author=Long, Tony |accessdate=13 March 2008|date=21 January 2008}}</ref> The discovery of the [[Kuiper belt]] in 1992 led many astronomers to debate whether Pluto should be considered a planet in its own right or part of the belt's larger structure.<ref>{{cite journal|author=Weissman, Paul R.|title=The Kuiper Belt| bibcode=1995ARA&A..33..327W|doi = 10.1146/annurev.aa.33.090195.001551|year=1995|journal=Annual Review of Astronomy and Astrophysics|volume=33|page=327}}</ref><ref>{{cite web|year=1999|title=The Status of Pluto:A clarification|work=[[International Astronomical Union]], Press release|url=http://www.iau.org/STATUS_OF_PLUTO.238.0.html|accessdate=25 May 2006|archiveurl=http://web.archive.org/web/20060615200253/http://www.iau.org/STATUS_OF_PLUTO.238.0.html |archivedate = 15 June 2006|deadurl=yes}}</ref> In 2006, the [[International Astronomical Union]] [[2006 definition of planet|defined the word "planet" for the first time]], reclassifying Pluto as a "[[dwarf planet]]" and making Neptune once again the last planet in the Solar System.<ref>{{cite news|url=http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf|title=IAU 2006 General Assembly: Resolutions 5 and 6|date=24 August 2006|publisher=IAU|format=PDF}}</ref>
 
Η διάμετρός του είναι περίπου 3,5 φορές μεγαλύτερη από αυτή της [[Γη]]ς, ενώ ο όγκος του είναι ίσος με 42 γήινους όγκους. Αντίθετα η [[πυκνότητα]] του είναι μικρή και για αυτό τον λόγο η [[μάζα]] του είναι 17 φορές μεγαλύτερη από τη μάζα της Γης. Η επιτάχυνση της βαρύτητας στην επιφάνειά του φτάνει τα 13,47 m/sec<sup>2
==Composition and structure==
</sup>.
[[File:Neptune, Earth size comparison.jpg|thumb|upright|A size comparison of Neptune and Earth]]
 
== Δομή ==
With a mass of 1.0243{{e|26}}&nbsp;kg,<ref name="fact" /> Neptune is an intermediate body between [[Earth]] and the larger [[gas giant]]s: its mass is 17 times that of Earth but just 1/19th that of [[Jupiter]].<ref group=lower-alpha name="mass">The mass of Earth is 5.9736{{e|24}}&nbsp;kg, giving a mass ratio of:
=== Εσωτερική δομή ===
: <math>\begin{smallmatrix}\frac{M_{Neptune}}{M_{Earth}} \ =\ \frac{1.02 \times 10^{26}}{5.97 \times 10^{24}} \ =\ 17.09\end{smallmatrix}</math>
Η εσωτερική δομή του Ποσειδώνα μοιάζει με αυτή του [[ουρανός (πλανήτης)|Ουρανού]]. Η ατμόσφαιρά του αποτελεί περίπου το 5 με 10 τις εκατό της συνολικής μάζας και και 10 με 20 % της ακτίνας του πλανήτη. Στις κατώτερες περιοχές της ατμόσφαιρας του πλανήτη υπάρχουν αυξημένες συγκεντρώσεις [[μεθάνιο|μεθανίου]], [[αμμωνία]]ς και νερού.
The mass of Uranus is 8.6810{{e|25}}&nbsp;kg, giving a mass ratio of:
: <math>\begin{smallmatrix}\frac{M_{Uranus}}{M_{Earth}} \ =\ \frac{8.68 \times 10^{25}}{5.97 \times 10^{24}}\ =\ 14.54\end{smallmatrix}</math>
The mass of Jupiter is 1.8986{{e|27}}&nbsp;kg, giving a mass ratio of:
: <math>\begin{smallmatrix}\frac{M_{Jupiter}}{M_{Neptune}} \ =\ \frac{1.90 \times 10^{27}}{1.02 \times 10^{26}}\ =\ 18.63\end{smallmatrix}</math>
Mass values from {{cite web
| last = Williams|first = David R.
| date = 29 November 2007
|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/
| title = Planetary Fact Sheet&nbsp;– Metric|publisher=NASA
| accessdate = 13 March 2008
}}</ref> Its [[surface gravity]] is surpassed only by [[Jupiter]].<ref name="Unsöld & Baschek 2001" /> Neptune's [[equator]]ial radius of 24,764&nbsp;km<ref name="Seidelmann Archinal A'hearn et al. 2007" /> is nearly four times that of Earth. Neptune and [[Uranus]] are often considered a subclass of gas giant termed "[[ice giant]]s", due to their smaller size and higher concentrations of [[volatiles]] relative to Jupiter and [[Saturn]].<ref name=Boss>{{cite journal
| first = Alan P.|last = Boss
| title = Formation of gas and ice giant planets
| journal = Earth and Planetary Science Letters
| year = 2002|volume = 202|issue = 3–4
| pages = 513–523|doi = 10.1016/S0012-821X(02)00808-7|bibcode = 2002E&PSL.202..513B}}</ref> In the search for [[extrasolar planet]]s Neptune has been used as a [[metonymy|metonym]]: discovered bodies of similar mass are often referred to as "Neptunes",<ref>{{cite news
| first = C.|last = Lovis|date = 18 May 2006
| coauthors = Mayor, M.; Alibert Y.; Benz W.
|url=http://www.eso.org/public/news/eso0618/
| title = Trio of Neptunes and their Belt
| publisher = [[European Southern Observatory|ESO]]
| accessdate = 25 February 2008}}</ref> just as astronomers refer to various extra-solar bodies as "Jupiters".
 
Σταδιακά, αυτή η περιοχή θερμαίνεται και συμπυκνώνεται σχηματίζοντας ένα υπέρθερμο, υγρό [[μανδύας (γεωλογία)|μανδύα]] με θερμοκρασία μεταξύ 2.000 και 5.000 βαθμών Κέλβιν. Ο μανδύας έχει μάζα 10 με 15 φορές μεγαλύτερη από τη γήινη και είναι πλούσιος σε νερό, αμμωνία και μεθάνιο. Αυτό το μείγμα αναφέρεται πολλές φορές ως πάγος, αν και είναι ένα καυτό, υπέρπυκνο υγρό. Σε βάθος 7.000 χιλιομέτρων οι συνθήκες είναι τέτοιες που το μεθάνιο μπορεί να διασπάται και σχηματίζονται [[διαμάντι]]α.<ref>{{cite journal
===Internal structure===
|last=Kerr|first=Richard A.
Neptune's internal structure resembles that of [[Uranus#Internal structure|Uranus]]. Its atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the way towards the core, where it reaches pressures of about 10&nbsp;[[Pascal (unit)|GPa]], or about 100,000 times that of Earth's atmosphere. Increasing concentrations of [[methane]], [[ammonia]] and water are found in the lower regions of the atmosphere.<ref name=hubbard/>
[[File:Neptune diagram.svg|325px|thumb|left| The internal structure of Neptune: <br> 1. Upper atmosphere, top clouds <br> 2. Atmosphere consisting of hydrogen, helium and methane gas <br> 3. Mantle consisting of water, ammonia and methane ices <br> 4. Core consisting of rock (silicates and nickel–iron)]]
The mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane.<ref name=Hamilton/> As is customary in planetary science, this mixture is referred to as [[volatiles|icy]] even though it is a hot, highly dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.<ref name=Atreya2006>{{cite journal
|last=Atreya|first=S.|coauthors=Egeler, P.; Baines, K.
|title=Water-ammonia ionic ocean on Uranus and Neptune?
|journal=Geophysical Research Abstracts
|volume=8|page=05179|year=2006|format=PDF
|url=http://www.cosis.net/abstracts/EGU06/05179/EGU06-J-05179-1.pdf}}</ref> The mantle may consist of a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down [[superionic water]] in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.<ref>[http://www.newscientist.com/article/mg20727764.500-weird-water-lurking-inside-giant-planets.html Weird water lurking inside giant planets], New Scientist,1 September 2010, Magazine issue 2776.</ref> At a depth of 7000&nbsp;km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.<ref>
{{cite journal
|last=Kerr |first=Richard A.
|title=Neptune May Crush Methane Into Diamonds
|journal=Science |year=1999 |volume=286
|issue=5437 |pagepages=25
|url=http://www.sciencemag.org/cgi/content/full/286/5437/25a
|doi=10.1126/science.286.5437.25a
|accessdate=2007-02-26
|pmid=10532884
|doi=10.1126/science.286.5437.25a}}</ref>
}}</ref> Very-high-pressure experiments at the [[Lawrence Livermore National Laboratory]] suggest that the base of the mantle may comprise an ocean of liquid diamond, with floating solid 'diamond-bergs'.<ref>{{cite web|url=http://news.discovery.com/space/alien-life-exoplanets/diamond-oceans-jupiter-uranus.htm|title=Diamond Oceans Possible on Uranus, Neptune|author=Bland, Eric |publisher=Discovery.com|date=January 15, 2010|accessdate=May 17, 2013}}</ref><ref>{{cite web|url=http://www.astronomynow.com/news/n1001/21diamond/|title=Oceans of diamond possible on Uranus and Neptune|author=Baldwin, Emily |publisher=astronomynow.com|date=January 21, 2010|accessdate=February 6, 2014}}</ref>
 
Ο πυρήνας του Ποσειδώνα αποτελείται από [[σίδηρος|σίδηρο]], [[νικέλιο]] και [[πυρίτιο]], με μάζα 1,2 φορές μεγαλύτερη από αυτή της Γης.<ref name=pass43>{{cite journal
The [[planetary core|core]] of Neptune is composed of iron, nickel and [[silicate]]s, with an interior model giving a mass about 1.2 times that of Earth.<ref name=pass43>{{cite journal
|last=Podolak|first=M.|coauthors=Weizman, A.; Marley, M.
|title=Comparative models of Uranus and Neptune
|journal=Planetary and Space Science
|year=1995|volume=43|issue=12|pages=1517–1522
|doi=10.1016/0032-0633(95)00061-5|bibcode=1995P&SS...43.1517P}}</ref> TheΗ pressureπίεση atστο theπυρήνα centre isείναι 7&nbsp;[[bar (unit)|Mbar]] (700 GPa), aboutεκατομμύρια twiceφορές asμεγαλύτερη highαπό asαυτή thatστην atεπιφάνεια theτης centre of EarthΓης, andκαι theμε temperatureθερμοκρασία may beπερίπου 5,400&nbsp; K.<ref name=hubbard/><ref name="nettelmann"/>{{cite web
|last=Nettelmann|first=N.
|coauthors=French, M.; Holst, B.; Redmer, R.|url=https://www.gsi.de/informationen/wti/library/plasma2006/PAPERS/TT-11.pdf
|format=PDF
|title=Interior Models of Jupiter, Saturn and Neptune
|publisher=University of Rostock|accessdate=25 February 2008
}}</ref>
 
===Atmosphere Ατμόσφαιρα ===
Σε μεγάλο υψόμετρο, η ατμόσφαιρα του Ποσειδώνα είναι 80% υδρογόνο και 19% ήλιο.<ref name=hubbard>{{cite journal
[[File:Neptune-Methane.jpg|thumb|Combined colour and near-[[infrared]] image of Neptune, showing bands of [[methane]] in its [[atmosphere]], and four of its [[Natural satellite|moons]], [[Proteus (moon)|Proteus]], [[Larissa (moon)|Larissa]], [[Galatea (moon)|Galatea]], and [[Despina (moon)|Despina]].]]
At high altitudes, Neptune's atmosphere is 80% [[hydrogen]] and 19% [[helium]].<ref name=hubbard>{{cite journal
|last=Hubbard|first=W. B.
|title=Neptune's Deep Chemistry
|journal=Science|year=1997
|volume=275|issue=5304|pages=1279–1280
|url=http://www.sciencemag.org/cgi/content/full/275/5304/1279
|accessdate=2008-02-19
|doi=10.1126/science.275.5304.1279
|pmid=9064785}}</ref> Ένα ίχνος ποσότητας του μεθανίου είναι επίσης παρόν. Οι ευδιάκριτες ζώνες απορρόφησης του μεθανίου συμβαίνουν σε μήκη κύματος πάνω από 600&nbsp;nm, στο κόκκινο και το υπέρυθρο τμήμα του [[φάσμα]]τος. Όπως και με τον Ουρανό, αυτή η απορρόφηση του ερυθρού φωτός από τον ατμοσφαιρικό μεθάνιο είναι μέρος αυτού που δίνει στο Ποσειδώνα το μπλε χρώμα του,<ref>{{cite web
|pmid=9064785}}</ref> A trace amount of methane is also present. Prominent absorption bands of methane occur at wavelengths above 600&nbsp;nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the [[atmospheric methane]] is part of what gives Neptune its blue hue,<ref>{{cite web
|last=Crisp|first=D.|coauthors=Hammel, H. B.
|date=14 June 14, 1995
|url =http://hubblesite.org/newscenter/archive/releases/1995/09/image/a/
|title =Hubble Space Telescope Observations of Neptune
|publisher = Hubble News Center
|accessdate = 22 April 2007-04-22
}}</ref> αν και η έντονη γαλάζια απόχρωση του Ποσειδώνα διαφέρει από την ηπιότερη, γαλαζοπράσινη του Ουρανού. Δεδομένου ότι η ατμοσφαιρική περιεκτικότητα σε μεθάνιο του Ποσειδώνα είναι παρόμοια με αυτή του Ουρανού, κάποιο άγνωστο ατμοσφαιρικό συστατικό θεωρείται ότι συμβάλλει στο χρώμα του Ποσειδώνα.
}}</ref>
although Neptune's vivid azure differs from Uranus's milder [[cyan]]. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.<ref name=bluecolour/>
 
Η ατμόσφαιρα Ποσειδώνα υποδιαιρείται σε δύο κύριες περιοχές: το χαμηλότερο στρώμα της [[τροπόσφαιρα]]ς, όπου θερμοκρασία μειώνεται με το υψόμετρο και τη [[στρατόσφαιρα]], όπου αυξάνεται η θερμοκρασία με το ύψος. Τα όρια μεταξύ των δύο, η τροπόπαυση, εμφανίζεται σε πίεση 0,1 bars (10 kPa).<ref name=atmo>{{cite web
Neptune's atmosphere is subdivided into two main regions; the lower [[troposphere]], where temperature decreases with altitude, and the [[stratosphere]], where temperature increases with altitude. The boundary between the two, the [[tropopause]], occurs at a pressure of {{convert|0.1|bar|kPa}}.<ref name="Lunine 1993" /> The stratosphere then gives way to the [[thermosphere]] at a pressure lower than 10<sup>−5</sup> to 10<sup>−4</sup> microbars (1 to 10&nbsp;Pa).<ref name="Lunine 1993" /> The thermosphere gradually transitions to the [[exosphere]].
|title=The Atmospheres of Uranus and Neptune
|last=Lunine|first=Jonathan I.
|publisher=Lunar and Planetary Observatory, University of Arizona
|year=1993|format=PDF
|url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1993ARA%26A..31..217L&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf
|accessdate=2008-03-10}}</ref> Η στρατόσφαιρα δίνει συνέχεια θέση για τη θερμόσφαιρα σε πίεση μικρότερη από 10<sup>−5</sup> με 10<sup>−4</sup> μικρομπάρ (1 έως 10 Pa ).<ref name=atmo /> Η θερμόσφαιρα βαθμιαία μεταβάλλεται στην εξώσφαιρα.
 
Τα μοντέλα δείχνουν ότι η τροπόσφαιρα του Ποσειδώνα είναι χωρισμένη σε σύννεφα διαφορετικών συνθέσεων ανάλογα με το υψόμετρο. Τα σύννεφα στο πάνω επίπεδο εμφανίζονται σε πιέσεις κάτω από ένα μπαρ, όπου η θερμοκρασία είναι κατάλληλη για να συμπυκνώσει το μεθάνιο. Για πιέσεις μεταξύ του ενός και πέντε ατμόσφαιρες (100 και 500 kPa), τα σύννεφα της αμμωνίας και του [[υδρόθειο|υδροθείου]] πιστεύεται ότι σχηματίζονται. Πάνω από μια πίεση των πέντε μπαρ, τα σύννεφα μπορεί να αποτελούνται από αμμωνία, θειούχο αμμώνιο, υδρόθειο και νερό. Βαθύτερη νέφη πάγου και νερού θα πρέπει να βρίσκονται σε πιέσεις περίπου 50 ατμοσφαιρών (5,0 MPa), όπου η θερμοκρασία φθάνει τους 0&nbsp;°C. Από κάτω, σύννεφα της [[αμμωνία]]ς και υδροθείου μπορεί να σχηματιστούν.
[[File:Neptune clouds.jpg|thumb|Bands of high-altitude clouds cast shadows on Neptune's lower cloud deck]]
 
Έχουν παρατηρηθεί στον Ποσειδώνα σύννεφα μεγάλου υψομέτρου να ρίχνουν σκιές στα αδιαφανή σύννεφα από κάτω. Υπάρχουν, επίσης, σε μεγάλο υψόμετρο λωρίδες νεφών που τυλίγονται γύρω από τον πλανήτη σε σταθερό γεωγραφικό πλάτος. Αυτές οι περιμετρικές ζώνες έχουν πλάτος της τάξης των 50-150 χλμ. και βρίσκονται περίπου 50-110 χλμ. πάνω από την επιφάνεια των νεφών.
Models suggest that Neptune's troposphere is banded by clouds of varying compositions depending on altitude. The upper-level clouds occur at pressures below one bar, where the temperature is suitable for methane to condense. For pressures between one and five bars (100 and 500 kPa), clouds of ammonia and [[hydrogen sulfide]] are believed to form. Above a pressure of five bars, the clouds may consist of ammonia, [[ammonium sulfide]], hydrogen sulfide and water. Deeper clouds of water ice should be found at pressures of about {{convert|50|bar|MPa}}, where the temperature reaches {{convert|273|K|C}}. Underneath, clouds of ammonia and hydrogen sulfide may be found.<ref name=elkins-tanton/>
 
To [[φάσμα]] του Ποσειδώνα δείχνει ότι η κατώτερη στρατόσφαιρα του είναι θολή λόγω της συμπύκνωσης των προϊόντων της υπεριώδους φωτόλυσης του μεθανίου, όπως το [[αιθάνιο]] και το [[ακετυλένιο]].<ref name= atmo /> Η στρατόσφαιρα είναι επίσης το σπίτι μικρών ποσοτήτων μονοξειδίου του άνθρακα και υδροκυάνιου.<ref name=atmo /><ref name=Encrenaz2003>{{cite journal|last=Encrenaz |first=Therese|title=ISO observations of the giant planets and Titan: what have we learnt?|journal=Planet. Space Sci.|volume=51|pages=89–103|year=2003|doi=10.1016/S0032-0633(02)00145-9| url=http://adsabs.harvard.edu/abs/2003P%26SS...51...89E}}</ref> Η στρατόσφαιρα του Ποσειδώνα είναι θερμότερη από ότι του Ουρανού, λόγω της αυξημένης συγκέντρωσης των υδρογονανθράκων.<ref name= atmo />
High-altitude clouds on Neptune have been observed casting shadows on the opaque cloud deck below. There are also high-altitude cloud bands that wrap around the planet at constant latitude. These circumferential bands have widths of 50–150&nbsp;km and lie about 50–110&nbsp;km above the cloud deck.<ref name=apj125/> These altitudes are in the layer where weather occurs, the troposphere. Weather does not occur in the higher stratosphere or thermosphere. Unlike Uranus, Neptune's composition has a higher volume of ocean, whereas Uranus has a smaller mantle.<ref>{{cite book|last=Frances|first=Peter|title=DK Universe|year=2008|publisher=DK Publishing|isbn=978-0-7566-3670-8|pages=196–201}}</ref>
 
Για λόγους που παραμένουν ασαφείς, η θερμόσφαιρα του Ποσειδώνα είναι σε ανώμαλα υψηλές θερμοκρασίες περίπου 750 Κ.<ref name=Broadfoot19989>{{cite journal|last=Broadfoot|first=A.L.|coauthors=Atreya, S.K.; Bertaux, J.L. et al.|title=Ultraviolet Spectrometer Observations of Neptune and Triton|journal=Science|volume=246|pages=1459–1456|year=1999| url=http://www-personal.umich.edu/~atreya/Articles/1989_Voyager_UV_Spectrometer.pdf|format=pdf|doi=10.1126/science.246.4936.1459|pmid=17756000|issue=4936}}</ref><ref name=Herbert1999>{{cite journal|last=Herbert|first=Floyd|coauthors=Sandel, Bill R. |title=Ultraviolet Observations of Uranus and Neptune|journal=Planet.Space Sci.|volume=47|pages=1119–1139|year=1999| url=http://adsabs.harvard.edu/abs/1999P%26SS...47.1119H |doi=10.1016/S0032-0633(98)00142-1}}</ref> Ο πλανήτης είναι πολύ μακριά από τον Ήλιο για να έχει παραχθεί αυτή η θερμότητα από την υπεριώδη ακτινοβολία. Ένας υποψήφιος μηχανισμός θέρμανσης είναι η ατμοσφαιρική αλληλεπίδραση με τα ιόντα του μαγνητικού πεδίου του πλανήτη. Άλλοι υποψήφιοι είναι κύματα βαρύτητας από το εσωτερικό τα οποία διαχέονται στην ατμόσφαιρα. Η θερμόσφαιρα περιέχει ίχνη διοξειδίου του άνθρακα και νερό, που μπορεί να έχουν κατατεθεί από εξωτερικές πηγές, όπως οι [[μετεωρίτης|μετεωρίτες]] και σκόνη.
Neptune's [[Visible spectrum|spectra]] suggest that its lower stratosphere is hazy due to condensation of products of ultraviolet [[photolysis]] of methane, such as ethane and acetylene.<ref name="Lunine 1993" /><ref name=hubbard/> The stratosphere is also home to trace amounts of [[carbon monoxide]] and [[hydrogen cyanide]].<ref name="Lunine 1993" /><ref name="Encrenaz 2003" /> The stratosphere of Neptune is warmer than that of Uranus due to the elevated concentration of hydrocarbons.<ref name="Lunine 1993" />
 
=== Μαγνητικό Πεδίο ===
For reasons that remain obscure, the planet's thermosphere is at an anomalously high temperature of about 750&nbsp;K.<ref name=Broadfoot19989>{{cite journal|last=Broadfoot|first=A.L.|coauthors=Atreya, S.K.; Bertaux, J.L. et al.|title=Ultraviolet Spectrometer Observations of Neptune and Triton|journal=Science|volume=246|pages=1459–1456|year=1999|url=http://www-personal.umich.edu/~atreya/Articles/1989_Voyager_UV_Spectrometer.pdf|format=PDF|doi=10.1126/science.246.4936.1459|pmid=17756000|issue=4936|bibcode=1989Sci...246.1459B}}</ref><ref name="Herbert & Sandel 1999" /> The planet is too far from the Sun for this heat to be generated by [[ultraviolet]] radiation. One candidate for a heating mechanism is atmospheric interaction with ions in the planet's [[Magnetosphere|magnetic field]]. Other candidates are [[gravity wave]]s from the interior that dissipate in the atmosphere. The thermosphere contains traces of [[carbon dioxide]] and water, which may have been deposited from external sources such as [[meteorite]]s and dust.<ref name=elkins-tanton/><ref name="Encrenaz 2003" />
Το [[μαγνητικό πεδίο]] του Ποσειδώνα μοιάζει με του [[Ουρανός (πλανήτης)|Ουρανού]] και έχει παράξενο προσανατολισμό. Ο άξονας του μαγνητικού πεδίου σχηματίζει γωνία περίπου 50° με τον άξονα περιστροφής του πλανήτη και το κέντρο απέχει περίπου 13.500 χιλιόμετρα από το κέντρο του Ποσειδώνα (0,55 ακτίνες). Ο λόγος της μεγάλης αυτής απόκλισης δεν είναι ακόμη γνωστός. Η ένταση του μαγνητικού πεδίου είναι περίπου ίση με το 1/5 της έντασης του γήινου μαγνητικού πεδίου. Το μαγνητικό πεδίο πιθανόν να δημιουργείται από κινήσεις αγώγιμου υλικού (ίσως ένας συνδυασμός αμμωνίας, μεθανίου και νερού) στα μεσαία στρώματά του.<ref name=elkins-tanton>Elkins-Tanton (2006):79–83.</ref>
 
===Magnetosphere Δακτύλιοι ===
[[Αρχείο:Neptune rings PIA02224.jpg|upright|thumb|right|Οι δακτύλιοι του Ποσειδώνα από το Βόγιατζερ 2]]
Neptune also resembles Uranus in its [[magnetosphere]], with a [[magnetic field]] strongly tilted relative to its [[rotation]]al axis at 47° and offset at least 0.55&nbsp;radii, or about 13500&nbsp;km from the planet's physical centre. Before ''Voyager 2'''s arrival at Neptune, it was hypothesised that Uranus's tilted magnetosphere was the result of its sideways rotation. In comparing the magnetic fields of the two planets, scientists now think the extreme orientation may be characteristic of flows in the planets' interiors. This field may be generated by [[convection|convective]] fluid motions in a thin spherical shell of
Στον Ποσειδώνα παρατηρήθηκαν πέντε δακτύλιοι, ανάλογοι με του [[Ουρανός (πλανήτης)|Ουρανού]] και του [[Κρόνος (πλανήτης)|Κρόνου]], οι οποίοι είναι αρκετά λεπτοί και αμυδροί. Αποτελούνται από παγωμένο μεθάνιο και από σωματίδια σκόνης που προέρχονται από θραύσματα συγκρούσεων. Επειδή τα υλικά αυτά δεν είναι ομοιόμορφα κατανεμημένα, μερικά τμήματα των δακτυλίων φαίνονται πιο λαμπερά από άλλα. Εκτείνονται σε απόσταση από 40.000 χιλιόμετρα πάνω από τα σύννεφα του πλανήτη και μέχρι τα 63.000 χιλιόμετρα, ενώ το πλάτος τους δεν ξεπερνάει τα 15 με 20 χιλιόμετρα. Ο εξωτερικός δακτύλιος ονομάζεται ''Δακτύλιος [[Άνταμς (δακτύλιος)|Άνταμς]]'' και περιέχει τρία ανεξάρτητα ''τόξα'': την Ελευθερία, την Ισότητα και την Αδελφότητα. Ο αμέσως επόμενος ονομάζεται [[Λεβεριέ (δακτύλιος)|Λεβεριέ]], ενώ στη συνέχεια βρίσκονται ο [[Λάσελ (δακτύλιος)|Λάσελ]] και ο [[Αραγκό (δακτύλιος)|Αραγκό]] και τέλος ο αμυδρός αλλά πλατύς δακτύλιος [[Γκάλε (δακτύλιος)|Γκάλε]].
[[Electrical conductor|electrically conducting]] liquids (probably a combination of ammonia, methane and water)<ref name=elkins-tanton>{{cite book
| last = Elkins-Tanton|first=Linda T.|year=2006
| title = Uranus, Neptune, Pluto, and the Outer Solar System
| publisher = Chelsea House|location=New York
| isbn = 978-0-8160-5197-7|pages=79–83}}</ref> resulting in a [[dynamo]] action.<ref>{{cite journal
|last=Stanley|first=Sabine|coauthors=Bloxham, Jeremy
|title=Convective-region geometry as the cause of Uranus' and Neptune's unusual magnetic fields
|journal=Nature|date=11 March 2004
|volume=428|pages=151–153
|doi=10.1038/nature02376
|pmid=15014493
|issue=6979|bibcode = 2004Natur.428..151S}}</ref>
 
== Κλίμα ==
The dipole component of the magnetic field at the magnetic equator of Neptune is about 14&nbsp;[[Tesla (unit)|microteslas]] (0.14&nbsp;[[Gauss (unit)|G]]).<ref name=Connerney1991>{{cite journal|last=Connerney|first=J.E.P.|coauthors=Acuna, Mario H.; Ness, Norman F.|title=The magnetic field of Neptune|year=1991|journal=Journal of Geophysics Research|volume=96|pages=19,023–42|bibcode=1991JGR....9619023C|last2=Acuna|last3=Ness|doi=10.1029/91JA01165}}</ref> The dipole [[magnetic moment]] of Neptune is about 2.2{{Esp|17}}&nbsp;T·m<sup>3</sup> (14&nbsp;μT·''R''<sub>''N''</sub><sup>3</sup>, where ''R''<sub>''N''</sub> is the radius of Neptune). Neptune's magnetic field has a complex geometry that includes relatively large contributions from non-dipolar components, including a strong [[quadrupole]] moment that may exceed the [[Magnetic dipole moment|dipole moment]] in strength. By contrast, Earth, Jupiter and Saturn have only relatively small quadrupole moments, and their fields are less tilted from the polar axis. The large quadrupole moment of Neptune may be the result of offset from the planet's centre and geometrical constraints of the field's dynamo generator.<ref name=science4936>{{cite journal
[[Αρχείο:Neptune storms.jpg|thumb|upright|right|Η μεγάλη Σκοτεινή Κηλίδα (επάνω), το Σκούτερ (μεσαίο λευκό νέφος),<ref name=scooter>{{cite web
|last=Ness|first=N. F.
|first=Sue|last=Lavoie|date=January 8, 1998
|coauthors=Acuña, M. H.; Burlaga, L. F.; Connerney, J. E. P.; Lepping, R. P.; Neubauer, F. M.
|title=Magnetic Fields at Neptune
|journal=Science|year=1989|volume=246
|issue=4936|pages=1473–1478
|doi=10.1126/science.246.4936.1473
|pmid=17756002|bibcode = 1989Sci...246.1473N}}
</ref><ref>{{cite web
|last=Russell|first=C. T.|coauthors=Luhmann, J. G.|year=1997
|url=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/nep_mag.html
|title=Neptune: Magnetic Field and Magnetosphere
|publisher=University of California, Los Angeles
|accessdate=10 August 2006
}}</ref>
 
Neptune's [[bow shock]], where the magnetosphere begins to slow the [[solar wind]], occurs at a distance of 34.9 times the radius of the planet. The [[magnetopause]], where the pressure of the magnetosphere counterbalances the solar wind, lies at a distance of 23–26.5 times the radius of Neptune. The tail of the magnetosphere extends out to at least 72 times the radius of Neptune, and very likely much farther.<ref name=science4936/>
 
===Planetary rings===
{{main|Rings of Neptune}}
[[File:neptunerings.jpg|upright|thumb|Neptune's rings, taken by ''Voyager 2'']]
Neptune has a [[planetary ring]] system, though one much less substantial than that of [[Rings of Saturn|Saturn]]. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue.<ref>{{cite book
| last = Cruikshank|first=Dale P.|title=Neptune and Triton
| publisher = [[University of Arizona Press]]|year=1996
| isbn = 978-0-8165-1525-7|pages=703–804}}</ref> The three main rings are the narrow Adams Ring, 63,000&nbsp;km from the centre of Neptune, the Le Verrier Ring, at 53,000&nbsp;km, and the broader, fainter Galle Ring, at 42,000&nbsp;km. A faint outward extension to the Le Verrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000&nbsp;km.<ref>{{cite web
|last=Blue|first=Jennifer|date=8 December 2004
|url=http://planetarynames.wr.usgs.gov/Page/Rings
|title=Nomenclature Ring and Ring Gap Nomenclature
|work=Gazetteer of Planetary|publisher=USGS
|accessdate=28 February 2008}}</ref>
 
The first of these planetary rings was discovered in 1968 by a team led by [[Edward Guinan]],<ref name=ring1>{{cite news
|last=Wilford|first=John N.|date=10 June 1982
|title=Data Shows 2 Rings Circling Neptune
|work=The New York Times
|url=http://query.nytimes.com/gst/fullpage.html?sec=technology&res=950DE3D71F38F933A25755C0A964948260&n=Top/News/Science/Topics/Space
|accessdate=29 February 2008}}</ref><ref>{{cite journal
|last=Guinan|first=E. F.
|coauthors=Harris, C. C.; Maloney, F. P.
|title=Evidence for a Ring System of Neptune
|journal=Bulletin of the American Astronomical Society
|year=1982|volume=14|page=658
|bibcode=1982BAAS...14..658G
|last2=Harris
|last3=Maloney
}}</ref> but it was later thought that this ring might be incomplete.<ref>{{cite journal
|last=Goldreich|first=P.
|coauthors=Tremaine, S.; Borderies, N. E. F.
|title=Towards a theory for Neptune's arc rings
|journal=Astronomical Journal
|year=1986|volume=92|pages=490–494
|bibcode=1986AJ.....92..490G
|doi=10.1086/114178
}}</ref> Evidence that the rings might have gaps first arose during a [[occultation|stellar occultation]] in 1984 when the rings obscured a star on immersion but not on emersion.<ref name="Nicholson90">{{cite journal
|author=Nicholson, P. D. et al.
|title=Five Stellar Occultations by Neptune: Further Observations of Ring Arcs
|journal= Icarus|year= 1990|volume= 87
|issue=1|page=1
|bibcode= 1990Icar...87....1N
|doi=10.1016/0019-1035(90)90020-A}}</ref> Images by ''Voyager 2'' in 1989 settled the issue by showing several faint rings. These rings have a clumpy structure,<ref name="Planetary Society">{{cite web
|url=http://www.planetary.org/explore/topics/our_solar_system/neptune/missions.html
|archiveurl=http://web.archive.org/web/20100211211122/http://www.planetary.org/explore/topics/our_solar_system/neptune/missions.html
|archivedate=2010-02-11
|title=Missions to Neptune|year=2007
|publisher=The Planetary Society|accessdate=11 October 2007}}</ref> the cause of which is not currently understood but which may be due to the gravitational interaction with small moons in orbit near them.<ref>{{cite news
|last=Wilford|first=John Noble
|date=15 December 1989
|title=Scientists Puzzled by Unusual Neptune Rings
|publisher=Hubble News Desk
|url=http://query.nytimes.com/gst/fullpage.html?res=950DE7DA1030F936A25751C1A96F948260
|accessdate=29 February 2008}}</ref>
 
The outermost ring, Adams, contains five prominent arcs now named ''Courage'', ''Liberté'', ''Egalité&nbsp;1'', ''Egalité&nbsp;2'' and ''Fraternité'' (Courage, Liberty, Equality and Fraternity).<ref>{{cite book
|first=Arthur N.|last=Cox|year=2001
|title=[[Clabon Allen|Allen]]'s Astrophysical Quantities
|publisher=Springer|isbn = 0-387-98746-0}}</ref> The existence of arcs was difficult to explain because the laws of motion would predict that arcs would spread out into a uniform ring over very short timescales. Astronomers now believe that the arcs are corralled into their current form by the gravitational effects of [[Galatea (moon)|Galatea]], a moon just inward from the ring.<ref>{{cite web
|last=Munsell|first=Kirk|date=13 November 2007
|coauthors=Smith, Harman; Harvey, Samantha
|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune&Display=Rings
|title=Planets: Neptune: Rings
|work=Solar System Exploration|publisher=NASA
|accessdate=29 February 2008
}}</ref><ref>{{cite journal
|last=Salo|first=Heikki|coauthors=Hänninen, Jyrki
|title=Neptune's Partial Rings: Action of Galatea on Self-Gravitating Arc Particles
|journal=Science|year=1998|volume=282
|issue=5391|pages=1102–1104
|doi=10.1126/science.282.5391.1102
|pmid=9804544|bibcode=1998Sci...282.1102S}}</ref>
 
Earth-based observations announced in 2005 appeared to show that Neptune's rings are much more unstable than previously thought. Images taken from the [[W. M. Keck Observatory]] in 2002 and 2003 show considerable decay in the rings when compared to images by ''Voyager 2''. In particular, it seems that the ''Liberté'' arc might disappear in as little as one century.<ref>{{cite web
|url=http://www.newscientist.com/article/mg18524925.900
|title=Neptune's rings are fading away
|date=26 March 2005|work=New Scientist|accessdate=6 August 2007}}</ref>
 
==Climate==
One difference between Neptune and Uranus is the typical level of meteorological activity. When the ''Voyager 2'' spacecraft flew by Uranus in 1986, that planet was visually quite bland. In contrast Neptune exhibited notable weather phenomena during the 1989 ''Voyager 2'' fly-by.<ref name=spot />
[[File:Neptune storms.jpg|thumb|upright|The [[Great Dark Spot]] (top), Scooter (middle white cloud),<ref name=scooter>{{cite web
|first=Sue|last=Lavoie|date=8 January 1998
|title=PIA01142: Neptune Scooter
|url=http://photojournal.jpl.nasa.gov/catalog/PIA01142
|publisher=NASA|accessdate=2006-03-26 March 2006}}</ref> andκαι theη [[SmallΜικρή DarkΣκοτεινή Spot]]Κηλίδα (bottomκάτω), withμε την contrastαντίθεση exaggeratedτονισμένη.]]
Μία διαφορά μεταξύ Ποσειδώνα και του Ουρανού είναι το τυπικό επίπεδο της μετεωρολογικής δραστηριότητας τους. Όταν το διαστημόπλοιο Βόγιατζερ 2 πέταξε πάνω από τον Ουρανό, το 1986, ο πλανήτης ήταν οπτικά πολύ ήπιος. Αντίθετα, ο Ποσειδώνας παρουσίασε αξιοσημείωτα καιρικά φαινόμενα κατά τη διάρκεια του 1989, όταν το Βόγιατζερ 2 τον προσέγγισε.<ref name=spot>{{cite web
|last=Lavoie|first=Sue|date=February 16, 2000
|url=http://photojournal.jpl.nasa.gov/catalog/PIA02245
|title=PIA02245: Neptune's blue-green atmosphere
|publisher=NASA JPL|accessdate=2008-02-28}}</ref>
 
Ο καιρός στον Ποσειδώνα χαρακτηρίζεται από εξαιρετικά δυναμικά συστήματα καταιγίδων, με ανέμους που αναπτύσσουν ταχύτητα περίπου 600 m / s -σχεδόν επίτευξη [[υπερηχητικός|υπερηχητικής]] ροής. Πιο τυπικά, με τον εντοπισμό της κίνησης των μόνιμων νεφών, η ταχύτητα του ανέμου έχει αποδειχθεί ότι κυμαίνεται από 20 m / s στην ανατολική κατεύθυνση έως 325 m / s προς τα δυτικά.<ref name="Hammel1989">{{cite journal
Neptune's weather is characterised by extremely dynamic storm systems, with winds reaching speeds of almost 600&nbsp;m/s (1340&nbsp;mph)—nearly attaining [[supersonic]] flow.<ref name="Suomi1991" /> More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20&nbsp;m/s in the easterly direction to 325&nbsp;m/s westward.<ref name="Hammel1989">{{cite journal
|last=Hammel|first=H. B.
|coauthors=Beebe, R. F.; De Jong, E. M.; Hansen, C. J.; Howell, C. D.; Ingersoll, A. P.; Johnson, T. V.; Limaye, S. S.; Magalhaes, J. A.; Pollack, J. B.; Sromovsky, L. A.; Suomi, V. E.; Swift, C. E.
Γραμμή 569 ⟶ 243 :
|journal=Science|year=1989|volume=245
|pages=1367–1369
|bibcodeurl=http://adsabs.harvard.edu/abs/1989Sci...245.1367H
|accessdate=2008-02-27
|doi=10.1126/science.245.4924.1367
|pmid=17798743
|issue=4924}}</ref> Στις κορυφές των νεφών, οι επικρατούντες άνεμοι πνέουν με εύρος ταχύτητας από τα 400 m / s κατά μήκος του ισημερινού έως 250 m / s στους πόλους. Οι περισσότεροι από τους άνεμους του Ποσειδώνα πνέουν σε μια κατεύθυνση αντίθετη με τη περιστροφή του πλανήτη.<ref name=burgess2>Burgess (1991):64–70.</ref> Η γενική εικόνα των ανέμων έδειξε ότι πνέουν σε ορθή φορά στα μεγάλα γεωγραφικά πλάτη έναντι ανάδρομης φοράς σε χαμηλότερα γεωγραφικά πλάτη. Η διαφορά στην κατεύθυνση της ροής, πιστεύεται ότι είναι ένα "επιφανειακό φαινόμενο» και δεν οφείλεται σε βαθύτερες ατμοσφαιρικές διεργασίες. Στον 70 ° νότιο γεωγραφικό παράλληλο, ένας πίδακας υψηλής ταχύτητας ταξιδεύει με ταχύτητα 300 m / s.<ref name=atmo />
|issue=4924}}</ref> At the cloud tops, the prevailing winds range in speed from 400&nbsp;m/s along the equator to 250&nbsp;m/s at the poles.<ref name=elkins-tanton/> Most of the winds on Neptune move in a direction opposite the planet's rotation.<ref name=burgess2>[[#Burgess|Burgess]] (1991):64–70.</ref> The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is believed to be a "skin effect" and not due to any deeper atmospheric processes.<ref name="Lunine 1993" /> At 70° S latitude, a high-speed jet travels at a speed of 300&nbsp;m/s.<ref name="Lunine 1993" />
 
To 2007 ανακαλύφθηκε ότι η ανώτερη τροπόσφαιρα του νότιου πόλου του Ποσειδώνα ήταν περίπου 10&nbsp;°C θερμότερη από τον υπόλοιπο Ποσειδώνα, έχει μέση τιμή περίπου -200&nbsp;°C (70 Κ).<ref>{{cite web
The abundance of methane, ethane and [[ethyne]] at Neptune's equator is 10–100 times greater than at the poles. This is interpreted as evidence for upwelling at the equator and subsidence near the poles.<ref name="Lunine 1993" />{{Clarify|date=March 2010}}<!-- Please clarify why this is evidence. -->
|title=Evidence for methane escape and strong seasonal and dynamical perturbations of Neptune's atmospheric temperatures
 
|author=Orton, G. S., Encrenaz T., Leyrat C., Puetter, R. and Friedson, A. J.|work=Astronomy and Astrophysics
In 2007, it was discovered that the upper troposphere of Neptune's south pole was about 10 K warmer than the rest of Neptune, which averages approximately {{convert|73|K|C|-1|abbr=on}}.<ref>{{cite journal|title=Evidence for methane escape and strong seasonal and dynamical perturbations of Neptune's atmospheric temperatures|author=Orton, G. S., Encrenaz T., Leyrat C., Puetter, R. and Friedson, A. J.|doi=10.1051/0004-6361:20078277|year=2007|journal=Astronomy and Astrophysics|volume=473|pages=L5–L8|bibcode=2007A&A...473L...5O}}</ref> The warmth differential is enough to let methane, which elsewhere lies frozen in Neptune's upper atmosphere, leak out as gas through the south pole and into space. The relative "hot spot" is due to Neptune's [[axial tilt]], which has exposed the south pole to the [[Sun]] for the last quarter of Neptune's year, or roughly 40 Earth years. As Neptune slowly moves towards the opposite side of the Sun, the south pole will be darkened and the north pole illuminated, causing the methane release to shift to the north pole.<ref>{{cite news
|url=http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361:20078277
|year=2007|accessdate=2008-03-10}}</ref> Η διαφορά θερμοκρασίας είναι αρκετή για να αφήσει το μεθάνιο, το οποίο αλλού βρίσκεται κατεψυγμένο στην ανώτερη ατμόσφαιρα του Ποσειδώνα, να διαρρεύσει ως αέριο μέσω του νότιου πόλου στο διάστημα. Το σχετικό "θερμό σημείο" οφείλεται στην κλίση του άξονα του Ποσειδώνα, με αποτέλεσμα να εκτίθεται ο νότιος πόλος προς τον Ήλιο για το τελευταίο τρίμηνο του έτους του Ποσειδώνα, ή περίπου 40 γήινα χρόνια. Καθώς ο Ποσειδώνας κινείται αργά προς την αντίθετη πλευρά του Ήλιου, ο νότιος πόλος θα σκοτεινιάσει και ο βόρειος πόλος θα φωτιστεί, προκαλώντας την απελευθέρωση μεθανίου να στραφεί στο βόρειο πόλο.<ref>{{cite news
|first=Glenn|last=Orton|coauthors=Encrenaz, Thérèse
|url=http://www.eso.org/public/newsoutreach/eso0741press-rel/pr-2007/pr-41-07.html
|title=A Warm South Pole? Yes, On Neptune!
|publisher=ESO|date=18 September 18, 2007
|accessdate=20 September 2007-09-20}}</ref>
 
Ο εντυπωσιακότερος σχηματισμός στην επιφάνεια του πλανήτη είναι η [[Μεγάλη Σκοτεινή Κηλίδα]] στο νότιο ημισφαίριο. Η Μεγάλη Σκοτεινή Κηλίδα είναι περίπου η μισή της Μεγάλης Ερυθρής Κηλίδας του Δία, με διάμετρο ίση με της Γης.
Because of seasonal changes, the cloud bands in the southern hemisphere of Neptune have been observed to increase in size and albedo. This trend was first seen in 1980 and is expected to last until about 2020. The long orbital period of Neptune results in seasons lasting forty years.<ref name=villard>{{cite news
|last=Villard|first=Ray|coauthors=Devitt, Terry
|date=15 May 2003
|title=Brighter Neptune Suggests A Planetary Change Of Seasons
|publisher=Hubble News Center
|url=http://hubblesite.org/newscenter/archive/releases/2003/17/text/
|accessdate=26 February 2008}}</ref>
 
===Storms= Τροχιά ==
Η μέση απόσταση μεταξύ Ποσειδώνα και του Ήλιου είναι 4,5 δισεκατομμύρια χιλιόμετρα (περίπου 30,1 AU), και ολοκληρώνει μια τροχιά κάθε 164,79 χρόνια. Στις 12 Ιουλίου 2011, ο Ποσειδώνας ολοκλήρωσε την πρώτη πλήρη τροχιά μετά την ανακάλυψή του, το 1846,<ref name="fact2">{{cite web
[[File:Neptune's Great Dark Spot.jpg|thumb|left|The Great Dark Spot, as imaged by ''Voyager 2'']]
In 1989, the [[Great Dark Spot]], an [[anticyclone|anti-cyclonic]] storm system spanning 13000×6600&nbsp;km,<ref name=spot>{{cite web
|last=Lavoie|first=Sue|date=16 February 2000
|url=http://photojournal.jpl.nasa.gov/catalog/PIA02245
|title=PIA02245: Neptune's blue-green atmosphere
|publisher=NASA JPL|accessdate=28 February 2008}}</ref> was discovered by [[NASA]]'s ''Voyager 2'' spacecraft. The storm resembled the [[Great Red Spot]] of Jupiter. Some five years later, on 2 November 1994, the [[Hubble Space Telescope]] did not see the Great Dark Spot on the planet. Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere.<ref>{{cite journal
|last=Hammel|first=H. B.
|coauthors=Lockwood, G. W.; Mills, J. R.; Barnet, C. D.
|title=Hubble Space Telescope Imaging of Neptune's Cloud Structure in 1994
|journal=Science|year=1995|volume=268
|issue=5218|pages=1740–1742
|doi=10.1126/science.268.5218.1740
|pmid=17834994
|bibcode=1995Sci...268.1740H
}}</ref>
 
The Scooter is another storm, a white cloud group farther south than the Great Dark Spot. Its nickname is due to the fact that when first detected in the months before the 1989 ''Voyager 2'' encounter it moved faster than the Great Dark Spot.<ref name=burgess2/> Subsequent images revealed even faster clouds. The [[Small Dark Spot]] is a southern cyclonic storm, the second-most-intense storm observed during the 1989 encounter. It initially was completely dark, but as ''Voyager 2'' approached the planet, a bright core developed and can be seen in most of the highest-resolution images.<ref>{{cite web
|last=Lavoie|first=Sue|date=29 January 1996
|url=http://photojournal.jpl.nasa.gov/catalog/PIA00064
|title=PIA00064: Neptune's Dark Spot (D2) at High Resolution
|publisher=NASA JPL|accessdate=28 February 2008}}</ref>
 
Neptune's dark spots are thought to occur in the [[troposphere]] at lower altitudes than the brighter cloud features,<ref>{{cite journal
|last=S. G.|first=Gibbard
|coauthors=de Pater, I.; Roe, H. G.; Martin, S.; Macintosh, B. A.; Max, C. E.
|title=The altitude of Neptune cloud features from high-spatial-resolution near-infrared spectra
|journal=Icarus|year=2003|volume=166
|issue=2|pages=359–374
|doi=10.1016/j.icarus.2003.07.006
|url=http://cips.berkeley.edu/research/depater_altitude.pdf
|format=PDF|accessdate=26 February 2008|bibcode=2003Icar..166..359G}}</ref> so they appear as holes in the upper cloud decks. As they are stable features that can persist for several months, they are thought to be [[vortex]] structures.<ref name=apj125/> Often associated with dark spots are brighter, persistent methane clouds that form around the [[tropopause]] layer.<ref>{{cite journal
|last=Stratman|first=P. W.
|coauthors=Showman, A. P.; Dowling, T. E.; Sromovsky, L. A.
|title=EPIC Simulations of Bright Companions to Neptune's Great Dark Spots
|journal=Icarus|year=2001|volume=151
|issue=2|pages=275–285|doi=10.1006/icar.1998.5918
|url=http://www.lpl.arizona.edu/~showman/publications/stratman-etal-2001.pdf
|format=PDF|accessdate=26 February 2008|bibcode=1998Icar..132..239L}}</ref> The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature. Dark spots may dissipate when they migrate too close to the equator or possibly through some other unknown mechanism.<ref>{{cite journal
|last=Sromovsky|first=L. A.
|coauthors=Fry, P. M.; Dowling, T. E.; Baines, K. H.
|title=The unusual dynamics of new dark spots on Neptune
|journal=Bulletin of the American Astronomical Society
|year=2000|volume=32|page=1005
|bibcode=2000DPS....32.0903S
|last2=Fry
|last3=Dowling
|last4=Baines}}</ref>
 
===Internal heating===
[[File:Different Faces Neptune.jpg|thumb|Four images taken a few hours apart with the NASA/ESA Hubble Space Telescope's Wide Field Camera 3<ref>{{cite web|url=http://www.spacetelescope.org/images/ann1115a/|title=Happy birthday Neptune|publisher=ESA/Hubble|accessdate=13 July 2011}}</ref>]]
 
Neptune's more varied weather when compared to Uranus is believed to be due in part to its higher [[internal heating]]. Although Neptune lies half again as far from the Sun as Uranus, and receives only 40% its amount of sunlight,<ref name="Lunine 1993" /> the two planets' surface temperatures are roughly equal.<ref name=williams>{{cite journal
|last=Williams|first=Sam
|title=Heat Sources Within the Giant Planets
|date=24 November 2004|publisher=UC Berkeley
|url=http://www.cs.berkeley.edu/~samw/research/projects/ay249/z_heat_sources/Paper_small.doc
|format=[[DOC (computing)|DOC]]|accessdate=20 February 2008}}</ref> The upper regions of Neptune's troposphere reach a low temperature of {{convert|51.8|K|C|abbr=on}}. At a depth where the atmospheric [[pressure]] equals {{convert|1|bar|kPa|lk=on}}, the temperature is {{convert|72.00|K|C|abbr=on}}.<ref>{{cite journal
|last=Lindal|first=Gunnar F.
|title=The atmosphere of Neptune&nbsp;– an analysis of radio occultation data acquired with Voyager 2
|journal=Astronomical Journal
|year=1992|volume=103|pages=967–982
|bibcode=1992AJ....103..967L
|doi=10.1086/116119}}</ref> Deeper inside the layers of gas, the temperature rises steadily. As with Uranus, the source of this heating is unknown, but the discrepancy is larger: Uranus only radiates 1.1 times as much energy as it receives from the Sun;<ref>{{cite web
|title=Class 12&nbsp;– Giant Planets&nbsp;– Heat and Formation
|work=3750&nbsp;– Planets, Moons & Rings|year=2004
|publisher=Colorado University, Boulder
|url=http://lasp.colorado.edu/~bagenal/3750/ClassNotes/Class12/Class12.html
|accessdate=13 March 2008}}</ref> while Neptune radiates about 2.61 times as much energy as it receives from the Sun.<ref>{{cite journal
|last=Pearl|first=J. C.|coauthors=Conrath, B. J.
|title=The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data
|journal=Journal of Geophysical Research Supplement|year=1991
|volume=96|pages=18,921–18,930
|bibcode=1991JGR....9618921P
|last2=Conrath|doi=10.1029/91ja01087}}</ref> Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. Depending on the thermal properties of its interior, the heat left over from Neptune's formation may be sufficient to explain its current heat flow, though it is more difficult to simultaneously explain [[Uranus]]'s lack of internal heat while preserving the apparent similarity between the two planets.<ref>Imke de Pater and Jack J. Lissauer (2001), ''[http://books.google.com/books?id=RaJdy3_VINQC&pg=PA224&lpg=PA224&dq=planet+neptune+heat+flow&source=bl&ots=ooEcNyQWA0&sig=nuZj0fnt86EkQM2YE1c9xKScQyU&hl=en&sa=X&ei=6e_3UZ-mIo_j4APV04HIDg&ved=0CEUQ6AEwAw#v=onepage&q=planet%20neptune%20heat%20flow&f=false Planetary Sciences]'', 1st edition, page 224.</ref>
 
==Orbit and rotation==
[[File:Neptune Orbit.gif|thumb|Neptune (red arc) completes one revolution around the Sun (center) for every 164.79 orbits of the Earth. The light blue object represents Uranus.]]
The average distance between Neptune and the Sun is {{nowrap|4.50 billion km}} (about 30.1&nbsp;AU), and it completes an orbit on average every 164.79&nbsp;years, subject to a variability of around ±0.1&nbsp;years.
 
On 11 July 2011, Neptune completed its first full [[Barycentric coordinates (astronomy)|barycentric]] orbit since its discovery in 1846,<ref name="obsjul711">{{cite news
|first=Robin| last=McKie
|url=http://www.guardian.co.uk/science/2011/jul/10/neptune-orbit-anniversary-astronomy
|title = Neptune's first orbit: a turning point in astronomy
|date = 9 July 2011
|work = The Guardian}}</ref><ref name=azureworld>{{cite web
|date=1 July 2011
|url=http://azureworld.blogspot.com/2011/07/neptune-completes-first-orbit-since.html
|title=Neptune Completes First Orbit Since Discovery: 11th July 2011 (at 21:48 U.T.±15min)
|accessdate=10 July 2011}}</ref> although it did not appear at its exact discovery position in our sky, because the Earth was in a different location in its 365.25-day orbit. Because of the motion of the Sun in relation to the [[Barycentre#Barycenter in astronomy|barycentre]] of the Solar System, on 11 July Neptune was also not at its exact discovery position in relation to the Sun; if the more common [[heliocentric]] coordinate system is used, the discovery longitude was reached on 12 July 2011.<ref name="fact2">{{cite web
|first=K.| last=Munsell|coauthors=Smith, H.; Harvey, S.
|url = http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune&Display=Facts
|title = Neptune: Facts & Figures
|date =13 November 13, 2007
|publisher = NASA|accessdate = 2007-08-14 August 2007}}</ref><ref name="UT2010-08"Horizons2011>{{cite web
|author=Anonymous|date=February 9, 2007
|date=26 August 2010
|url=http://home.comcast.net/~kpheider/nept2011.txt
|title=Clearing the Confusion on Neptune’s Orbit
|publisher=Universe Today
|author=Nancy Atkinson
|url=http://www.universetoday.com/72088/clearing-the-confusion-on-neptune%E2%80%99s-orbit/
|accessdate=2011-07-10}} [http://twitter.com/#!/elakdawalla/status/21525820626 (Bill Folkner at JPL)]</ref><ref name=Horizons2011>{{cite web
|author=Anonymous|date=16 November 2007
|url=http://home.surewest.net/kheider/astro/nept2011.txt
|title=Horizons Output for Neptune 2010–2011
|accessdate=2008-02-25|archiveurl=http://web.archive.org/20081210085807/home.comcast.net/~kpheider/nept2011.txt|archivedate=2008-12-10}}</ref> αν και δεν εμφανίστηκε στην ακριβή θέση του ουρανού που ανακαλύφθηκε επειδή η Γη ήταν σε διαφορετική θέση στις 365,25 ημέρες τροχιά της.
|accessdate=25 February 2008}}—Numbers generated using the Solar System Dynamics Group, Horizons On-Line Ephemeris System.</ref>
 
Η ελλειπτική τροχιά του Ποσειδώνα έχει κλίση 1,77 μοιρών σε σχέση με τη Γη. Λόγω της [[εκκεντρότητα]]ς 0,011, η απόσταση μεταξύ Ποσειδώνα και του Ήλιου ποικίλλει κατά 101 εκατομμύρια χιλιόμετρα μεταξύ [[περιήλιο|περιηλίου]] και [[αφήλιο|αφηλίου]], το εγγύτερο και το πιο απομακρυσμένο σημείο της τροχιάς του πλανήτη γύρω από τον Ήλιο κατά μήκος της τροχιάς του, αντίστοιχα.<ref name=horizons/>
The elliptical orbit of Neptune is inclined 1.77° compared to the Earth. Because of an [[orbital eccentricity|eccentricity]] of 0.011, the distance between Neptune and the Sun varies by 101&nbsp;million&nbsp;km between [[perihelion]] and [[aphelion]], the nearest and most distant points of the planet from the Sun along the orbital path, respectively.<ref name=horizons/>
 
TheΗ axialκλίση tiltτου ofάξονα Neptuneπεριστροφής isτου Ποσειδώνα είναι 28.,32 °,<ref>{{cite web
|last=Williams|first=David R.|date=6 January 6, 2005
|url=http://nssdc.gsfc.nasa.gov/planetary/planetfact.html
|title=Planetary Fact Sheets|publisher=NASA
|accessdate=2008-02-28}}</ref> κλίση παρόμοια με αυτή της Γης (23 °) και του Άρη (25 °). Ως αποτέλεσμα, αυτός ο πλανήτης έχει παρόμοιες εποχικές αλλαγές. Ωστόσο, η μεγάλη τροχιακή περίοδος του Ποσειδώνα σημαίνει ότι οι εποχές διαρκούν σαράντα γήινα χρόνια. Η περίοδος περιστροφής (ημέρα) είναι περίπου 16,11 ώρες.<ref name="fact2" /> Η κλίση του άξονά του είναι συγκρίσιμη με της Γης, η μεταβολή της διάρκειας της μέρας κατά τη διάρκεια του μακρού έτος δεν είναι περισσότερο ακραία.
|accessdate=28 February 2008}}</ref> which is similar to the tilts of Earth (23°) and Mars (25°). As a result, this planet experiences similar seasonal changes. The long orbital period of Neptune means that the seasons last for forty Earth years.<ref name=villard/> Its sidereal rotation period (day) is roughly 16.11&nbsp;hours.<ref name="fact2" /> Since its axial tilt is comparable to the Earth's, the variation in the length of its day over the course of its long year is not any more extreme.
 
== Δορυφόροι ==
Because Neptune is not a solid body, its atmosphere undergoes [[differential rotation]]. The wide equatorial zone rotates with a period of about 18&nbsp;hours, which is slower than the 16.1-hour rotation of the planet's magnetic field. By contrast, the reverse is true for the polar regions where the rotation period is 12&nbsp;hours. This differential rotation is the most pronounced of any planet in the Solar System,<ref>{{cite journal
Ο Ποσειδώνας έχει 14 γνωστούς δορυφόρους, εκ των οποίων τον κατά πολύ μεγαλύτερο από τους υπόλοιπους Τρίτωνα, που αποτελεί το 99,5% μάζας των δορυφόρων του Ποσειδώνα και είναι ο μόνος με σφαιρικό σχήμα, και ανακαλύφθηκε μόλις 17 μέρες μετά τον Ποσειδώνα. Επίσης, ο Τρίτωνας είναι ο μόνος μεγάλος δορυφόρος που περιστρέφεται ανάδρομα, υποδεικνύοντας ότι πιθανόν ήταν ένας [[πλανήτης νάνος]] της ζώνης του Κάιπερ που αιχμαλωτίστηκε από τη βαρύτητα του Ποσειδώνα.<ref>{{cite journal
|last=Hubbard|first=W. B.
|coauthors=Nellis, W. J.; Mitchell, A. C.; Holmes, N. C.; McCandless, P. C.; Limaye, S. S.
|title=Interior Structure of Neptune: Comparison with Uranus
|journal=Science|year=1991|volume=253
|issue=5020|pages=648–651
|doi=10.1126/science.253.5020.648
|pmid=17772369|bibcode = 1991Sci...253..648H}}</ref> and it results in strong latitudinal wind shear.<ref name=apj125>{{cite journal
|last=Max|first=C. E.
|coauthors=Macintosh, B. A.; Gibbard, S. G.; Gavel, D. T.; Roe, H. G.; de Pater, I.; [[Andrea Ghez|Ghez, A. M.]]; Acton, D. S.; Lai, O.; Stomski, P.; Wizinowich, P. L.
|title=Cloud Structures on Neptune Observed with Keck Telescope Adaptive Optics
|journal=The Astronomical Journal,
|year=2003|volume=125|issue=1|pages=364–375
|bibcode=2003AJ....125..364M
|doi=10.1086/344943
}}</ref>
 
===Orbital resonances===
{{main|Kuiper belt|Resonant trans-Neptunian object|Neptune trojan}}
[[File:TheKuiperBelt classes-en.svg|thumb|250px| A diagram showing the major orbital resonances in the Kuiper belt caused by Neptune: the highlighted regions are the 2:3 resonance (plutinos), the nonresonant [[Classical Kuiper belt object|"classical belt"]] (cubewanos), and the 1:2 resonance ([[twotino]]s).]]
Neptune's orbit has a profound impact on the region directly beyond it, known as the Kuiper belt. The Kuiper belt is a ring of small icy worlds, similar to the [[asteroid belt]] but far larger, extending from Neptune's orbit at 30&nbsp;AU out to about 55&nbsp;AU from the Sun.<ref>{{cite journal
|title=Collisional Erosion in the Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU Kuiper Gap
|first=S. Alan|last=Stern
|publisher=Geophysical, Astrophysical, and Planetary Sciences, Space Science Department, Southwest Research Institute
|doi=10.1086/304912
|year=1997
|last2=Colwell
|first2=Joshua E.
|journal=The Astrophysical Journal
|volume=490
|issue=2
|pages=879–882
|bibcode=1997ApJ...490..879S
}}</ref> Much in the same way that Jupiter's gravity dominates the [[asteroid belt]], shaping its structure, so Neptune's gravity dominates the [[Kuiper belt]]. Over the age of the Solar System, certain regions of the Kuiper belt became destabilised by Neptune's gravity, creating gaps in the Kuiper belt's structure. The region between 40 and 42&nbsp;AU is an example.<ref>{{cite journal
|title=Large Scattered Planetesimals and the Excitation of the Small Body Belts
|first=Jean-Marc|last=Petit|coauthors=Morbidelli, Alessandro; Valsecchi, Giovanni B.
|url=https://www.oca.eu/morby/papers/6166a.pdf|doi=10.1006/icar.1999.6166
|year=1999|accessdate=23 June 2007|format=PDF
|journal=Icarus
|volume=141
|issue=2
|page=367|bibcode = 1999Icar..141..367P }}</ref>
 
There do exist orbits within these empty regions where objects can survive for the age of the Solar System. These [[Orbital resonance|resonances]] occur when Neptune's orbital period is a precise fraction of that of the object, such as 1:2, or 3:4. If, say, an object orbits the Sun once for every two Neptune orbits, it will only complete half an orbit by the time Neptune returns to its original position. The most heavily populated resonance in the Kuiper belt, with over 200 known objects,<ref>{{cite web
|title=List Of Transneptunian Objects
|publisher=Minor Planet Center
|url=http://www.minorplanetcenter.org/iau/lists/TNOs.html
|accessdate=25 October 2010}}</ref> is the 2:3 resonance. Objects in this resonance complete 2 orbits for every 3 of Neptune, and are known as [[plutino]]s because the largest of the known Kuiper belt objects, [[Pluto]], is among them.<ref>{{cite web
|last=Jewitt|first=David|year=2004
|url=http://www2.ess.ucla.edu/~jewitt/kb/plutino.html
|title=The Plutinos|publisher=UCLA
|accessdate=28 February 2008}}</ref> Although Pluto crosses Neptune's orbit regularly, the 2:3 resonance ensures they can never collide.<ref>{{cite journal
|last=Varadi|first=F.
|title=Periodic Orbits in the 3:2 Orbital Resonance and Their Stability
|journal=The Astronomical Journal
|year=1999|volume=118
|issue=5|pages=2526–2531
|bibcode=1999AJ....118.2526V
|doi=10.1086/301088}}</ref> The 3:4, 3:5, 4:7 and 2:5 resonances are less populated.<ref>{{cite book|title=Beyond Pluto: Exploring the outer limits of the solar system |author=John Davies|publisher=Cambridge University Press|year=2001|page=104|isbn = 0-521-80019-6}}</ref>
 
Neptune possesses a number of [[Trojan (astronomy)|trojan objects]] occupying the [[Sun]]-Neptune {{L4}} [[Lagrangian point]]—a gravitationally stable region leading it in its orbit.<ref>{{cite journal |title=Resonance Occupation in the Kuiper Belt: Case Examples of the 5 : 2 and Trojan Resonances |first=E. I.|last=Chiang|coauthors=Jordan, A. B.; Millis, R. L.; M. W. Buie; Wasserman, L. H.; Elliot, J. L.; Kern, S. D.; Trilling, D. E.; Meech, K. J.; Wagner, R. M. |year=2003 |doi=10.1086/375207 |journal=The Astronomical Journal |volume=126 |pages=430–443 |bibcode=2003AJ....126..430C|arxiv = astro-ph/0301458}}</ref> [[Neptune trojan]]s can be viewed as being in a 1:1 resonance with Neptune. Some Neptune trojans are remarkably stable in their orbits, and are likely to have formed alongside Neptune rather than being captured. The first and so far only object identified as associated with Neptune's trailing {{L5}} [[Lagrangian point]] is [[2008 LC18]].<ref name="Sheppard">{{Cite journal|last = Sheppard|first = Scott S.|authorlink = Scott S. Sheppard|coauthors = Trujillo, Chadwick A.|title = Detection of a Trailing (L5) Neptune Trojan|journal = [[Science (journal)|Science]]|volume = 329|issue = 5997|page = 1304|date = 10 September 2010|doi = 10.1126/science.1189666|pmid=20705814|bibcode = 2010Sci...329.1304S}}</ref> Neptune also has a temporary [[quasi-satellite]], {{mpl|(309239) 2007 RW|10}}.<ref name="quasi">{{cite journal |last=de la Fuente Marcos & de la Fuente Marcos |title=(309239) 2007 RW10: a large temporary quasi-satellite of Neptune |journal=Astronomy and Astrophysics Letters |volume=545 |pages=L9 |year=2012 |arxiv=1209.1577 |bibcode=2012A%26A...545L...9D |doi=10.1051/0004-6361/201219931 |first1=C. |last2=De La Fuente Marcos |first2=R.}}</ref> The object has been a quasi-satellite of Neptune for about 12,500 years and it will remain in that dynamical state for another 12,500 years. It is likely a captured object.<ref name=quasi/>
 
==Formation and migration==
{{main|Formation and evolution of the Solar System|Nice model}}
 
[[File:Lhborbits.png|thumb|400px|A simulation showing the outer planets and Kuiper belt: a) before Jupiter and Saturn reached a 2:1 resonance; b) after inward scattering of Kuiper belt objects following the orbital shift of Neptune; c) after ejection of scattered Kuiper belt bodies by Jupiter]]
 
The formation of the ice giants, Neptune and Uranus, has proven difficult to model precisely. Current models suggest that the matter density in the outer regions of the Solar System was too low to account for the formation of such large bodies from the traditionally accepted method of core [[Accretion (astrophysics)|accretion]], and various hypotheses have been advanced to explain their creation. One is that the ice giants were not created by core accretion but from instabilities within the original [[protoplanetary disc]] and later had their atmospheres blasted away by radiation from a nearby massive [[OB star]].<ref name=Boss/>
 
An alternative concept is that they formed closer to the Sun, where the matter density was higher, and then subsequently [[Planetary migration|migrated]] to their current orbits after the removal of the gaseous protoplanetary disc.<ref>{{cite journal
|title=The formation of Uranus and Neptune among Jupiter and Saturn
|first=Edward W. |last=Thommes
|coauthors=Duncan, Martin J.; Levison, Harold F.
|year=2001
|doi=10.1086/339975
|journal=The Astronomical Journal
|volume=123
|issue=5
|pages=2862–2883
|arxiv=astro-ph/0111290
|bibcode=2002AJ....123.2862T
}}</ref> This hypothesis of migration after formation is currently favoured, due to its ability to better explain the occupancy of the populations of small objects observed in the trans-Neptunian region.<ref>{{cite web
|title=Orbital shuffle for early solar system
|first=Kathryn|last= Hansen|publisher=Geotimes
|url=http://www.geotimes.org/june05/WebExtra060705.html
|date=7 June 2005|accessdate=26 August 2007}}</ref> The current most widely accepted<ref name="Crida2009">
{{cite journal
|last=Crida |first=A.
|year=2009
|title=Solar System formation
|journal=Reviews in Modern Astronomy
|volume=21 |arxiv=0903.3008
|bibcode = 2009arXiv0903.3008C
|doi=10.1002/9783527629190.ch12
|page=3008}}</ref><ref name="Desch07">{{cite journal|last=Desch|first=S. J.|year=2007|title=Mass Distribution and Planet Formation in the Solar Nebula|journal=The Astrophysical Journal|volume=671|issue=1|pages=878–893 |doi=10.1086/522825|bibcode=2007ApJ...671..878D}}</ref><ref name="Smith2009">{{cite journal|last=Smith|first=R.|coauthors=L. J. Churcher; M. C. Wyatt; M. M. Moerchen; C. M. Telesco|year=2009|title=Resolved debris disc emission around η Telescopii: a young solar system or ongoing planet formation?|journal=Astronomy and Astrophysics|volume=493|issue=1|pages=299–308|doi=10.1051/0004-6361:200810706|bibcode=2009A&A...493..299S|arxiv = 0810.5087 }}</ref> explanation of the details of this hypothesis is known as the [[Nice model]], which explores the effect of a migrating Neptune and the other giant planets on the structure of the Kuiper belt.
 
==Moons==
{{main|Moons of Neptune}}
{{For|a timeline of discovery dates|Timeline of discovery of Solar System planets and their moons}}
[[File:Neptune-visible.jpg|thumb|Natural-colour view of Neptune with Proteus (top), Larissa (lower right) and Despina (left), from the Hubble Space Telescope]]
 
Neptune has 14 known [[natural satellite|moons]].<ref name="fact" /><ref>[http://www.news.com.au/technology/sci-tech/hubble-space-telescope-discovers-fourteenth-tiny-moon-orbiting-neptune/story-fn5fsgyc-1226679913807 Hubble Space Telescope discovers fourteenth tiny moon orbiting Neptune | Space, Military and Medicine]. News.com.au (2013-07-16). Retrieved on 2013-07-28.</ref> The largest by far, comprising more than 99.5% of the mass in orbit around Neptune<ref group=lower-alpha>Mass of Triton: 2.14{{e|22}}&nbsp;kg. Combined mass of 12 other known moons of Neptune: 7.53{{e|19}} kg, or 0.35%. The mass of the rings is negligible.</ref> and the only one massive enough to be [[spheroid]]al, is [[Triton (moon)|Triton]], discovered by [[William Lassell]] just 17&nbsp;days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a [[retrograde orbit]], indicating that it was captured rather than forming in place; it was probably once a [[dwarf planet]] in the Kuiper belt.<ref>{{cite journal
|first=Craig B.|last=Agnor|coauthors=Hamilton, Douglas P.
|title=Neptune's capture of its moon Triton in a binary–planet gravitational encounter
Γραμμή 812 ⟶ 289 :
|volume=441|issue=7090|pages=192–194
|doi=10.1038/nature04792
|url= http://www.nature.com/nature/journal/v441/n7090/abs/nature04792.html
|accessdate=2008-02-28
|publisher=Nature Publishing Group
|pmid=16688170}}</ref>
|pmid=16688170|bibcode=2006Natur.441..192A}}</ref> It is close enough to Neptune to be locked into a [[synchronous rotation]], and it is slowly spiralling inward because of [[tidal acceleration]]. It will eventually be torn apart, in about 3.6&nbsp;billion years, when it reaches the [[Roche limit]].<ref>{{cite journal
|first= Christopher F.|last=Chyba
|coauthors=Jankowski, D. G.; Nicholson, P. D.
|title = Tidal evolution in the Neptune-Triton system
|journal = Astronomy and Astrophysics
|year = 1989|volume = 219
|issue = 1–2|pages=L23–L26
|bibcode = 1989A&A...219L..23C
|publisher=EDP Sciences
|last2= Jankowski
|last3= Nicholson}}</ref> In 1989, Triton was the coldest object that had yet been measured in the solar system,<ref>{{cite news
|last=Wilford|first=John N.|work=The New York Times
|date=29 August 1989
|title=Triton May Be Coldest Spot in Solar System
|url=http://query.nytimes.com/gst/fullpage.html?res=950DE4DC1138F93AA1575BC0A96F948260
|accessdate=29 February 2008}}</ref> with estimated temperatures of {{convert|38|K|C|0}}.<ref>{{cite journal
|author=Nelson, R. M.; Smythe, W. D.; Wallis, B. D.; Horn, L. J.; Lane, A. L.; Mayo, M. J.
|title=Temperature and Thermal Emissivity of the Surface of Neptune's Satellite Triton
|journal=Science|year=1990|volume=250
|issue=4979|pages=429–431
|doi=10.1126/science.250.4979.429
|pmid=17793020|bibcode = 1990Sci...250..429N|last2=Smythe
|last3=Wallis
|last4=Horn
|last5=Lane
|last6=Mayo
}}</ref>
 
Neptune's second known satellite (by order of discovery), the irregular moon [[Nereid (moon)|Nereid]], has one of the most eccentric orbits of any satellite in the solar system. The eccentricity of 0.7512 gives it an [[apoapsis]] that is seven times its [[periapsis]] distance from Neptune.<ref group=lower-alpha><math>\begin{smallmatrix}\frac{r_{a}}{r_{p}} = \frac{2}{1-e}-1 = 2/0.2488-1=7.039.\end{smallmatrix}</math></ref>
 
[[File:Proteus (Voyager 2).jpg|thumb|upright|left|Neptune's moon [[Proteus (moon)|Proteus]]]]
From July to September 1989, ''Voyager 2'' discovered six new Neptunian moons.<ref name="science4936">{{cite journal
|last=Stone|first=E. C.|coauthors=Miner, E. D.
|title=The Voyager 2 Encounter with the Neptunian System
|journal=Science|year=1989|volume=246
|issue=4936|pages=1417–1421
|doi=10.1126/science.246.4936.1417
|pmid=17755996|bibcode=1989Sci...246.1417S}}</ref> Of these, the irregularly shaped [[Proteus (moon)|Proteus]] is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity.<ref name=Brown>{{cite web
|url=http://web.gps.caltech.edu/~mbrown/dwarfplanets/
|title=The Dwarf Planets
|first=Michael E.|last=Brown|authorlink=Michael E. Brown
|publisher=California Institute of Technology, Department of Geological Sciences
|accessdate=9 February 2008}}</ref> Although the second-most-massive Neptunian moon, it is only 0.25% the mass of Triton. Neptune's innermost four moons—[[Naiad (moon)|Naiad]], [[Thalassa (moon)|Thalassa]], [[Despina (moon)|Despina]] and [[Galatea (moon)|Galatea]]—orbit close enough to be within Neptune's rings. The next-farthest out, [[Larissa (moon)|Larissa]], was originally discovered in 1981 when it had occulted a star. This occultation had been attributed to ring arcs, but when ''Voyager 2'' observed Neptune in 1989, it was found to have been caused by the moon. Five new irregular moons discovered between 2002 and 2003 were announced in 2004.<ref name="HolmanKavelaarsGrav2004">
{{cite doi|10.1038/nature02832}}
</ref><ref>{{cite news
|url=http://news.bbc.co.uk/2/hi/science/nature/3578210.stm
|title=Five new moons for planet Neptune
|date=18 August 2004
|publisher=BBC News |accessdate=6 August 2007}}</ref> A new moon and the smallest yet, [[S/2004 N 1]], was found in 2013. Since Neptune was the Roman god of the sea, the planet's moons have been named after lesser sea gods.<ref name=USGS/>
 
==Observation==
Neptune is never visible to the [[naked eye]], having a brightness between [[Apparent magnitude|magnitudes]] +7.7 and +8.0,<ref name="fact" /><ref name=ephemeris>{{cite web
|last=Espenak|first=Fred|date=20 July 2005
|url=http://eclipse.gsfc.nasa.gov/TYPE/TYPE.html
|title=Twelve Year Planetary Ephemeris: 1995–2006
|publisher=NASA|accessdate=1 March 2008}}</ref> which can be outshone by Jupiter's [[Galilean moons]], the [[dwarf planet]] [[Ceres (dwarf planet)|Ceres]] and the [[asteroid]]s [[4 Vesta]], [[2 Pallas]], [[7 Iris]], [[3 Juno]] and [[6 Hebe]].<ref>See the respective articles for magnitude data.</ref> A telescope or strong binoculars will resolve Neptune as a small blue disk, similar in appearance to Uranus.<ref>[[#Moore|Moore]] (2000):207.</ref>
 
Because of the distance of Neptune from the Earth, the [[angular diameter]] of the planet only ranges from 2.2 to 2.4&nbsp;[[arcsecond]]s,<ref name="fact" /><ref name=ephemeris/> the smallest of the Solar System planets. Its small apparent size has made it challenging to study visually. Most telescopic data was fairly limited until the advent of [[Hubble Space Telescope]] and large ground-based telescopes with [[adaptive optics]].<ref>In 1977, for example, even the rotation period of Neptune remained uncertain. {{cite journal
|last=Cruikshank|first=D. P.
|title=On the rotation period of Neptune
|journal=Astrophysical Journal, Part 2&nbsp;– Letters to the Editor
|date=1 March 1978|volume=220
|pages=L57–L59
|bibcode=1978ApJ...220L..57C
|publisher=University of Chicago Press
|doi=10.1086/182636}}</ref><ref>{{cite journal
|last=Max|first=C.
|title=Adaptive Optics Imaging of Neptune and Titan with the W.M. Keck Telescope
|journal=Bulletin of the American Astronomical Society
|year=1999|volume=31|page=1512
|bibcode=1999BAAS...31.1512M
|last2=MacIntosh
|first2=B.
|last3=Gibbard
|first3=S.
|last4=Roe
|first4=H.
|last5=De Pater
|first5=I.
|last6=Ghez
|first6=A.
|last7=Acton
|first7=S.
|last8=Wizinowich
|first8=P.
|last9=Lai
|first9=O.
|display-authors=9
}}</ref>
 
From the Earth, Neptune goes through apparent [[Retrograde and direct motion|retrograde motion]] every 367&nbsp;days, resulting in a looping motion against the background stars during each [[Opposition (astronomy and astrology)|opposition]]. These loops carried it close to the 1846 discovery coordinates in April and July 2010 and again in October and November 2011.<ref name=Horizons2011/>
 
Observation of Neptune in the radio-frequency band shows that the planet is a source of both continuous emission and irregular bursts. Both sources are believed to originate from the planet's rotating magnetic field.<ref name=elkins-tanton/> In the [[infrared]] part of the spectrum, Neptune's storms appear bright against the cooler background, allowing the size and shape of these features to be readily tracked.<ref>{{cite journal
|last= Gibbard|first=S. G.
|coauthors=Roe, H.; de Pater, I.; Macintosh, B.; Gavel, D.; Max, C. E.; Baines, K. H.; Ghez, A.
|title=High-Resolution Infrared Imaging of Neptune from the Keck Telescope
|journal=Icarus|year=1999|volume=156
|issue= 1|pages=1–15
|doi=10.1006/icar.2001.6766|bibcode=2002Icar..156....1G}}</ref>
 
==Exploration==
{{main|Exploration of Neptune}}
[[File:Triton moon mosaic Voyager 2 (large).jpg|thumb|A ''Voyager 2'' mosaic of Triton]]
''[[Voyager 2]]''<nowiki>'</nowiki>s closest approach to Neptune occurred on 25 August 1989. Because this was the last major planet the spacecraft could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, similarly to what was done for ''[[Voyager 1]]''<nowiki>'</nowiki>s encounter with [[Saturn]] and its moon [[Titan (moon)|Titan]]. The images relayed back to Earth from ''Voyager 2'' became the basis of a 1989 [[Public Broadcasting Service|PBS]] all-night program, ''Neptune All Night''.<ref>{{cite web
|last=Phillips|first=Cynthia|date=5 August 2003
|url=http://www.seti.org/about-us/voices/phillips-080503.php
|title=Fascination with Distant Worlds
|accessdate=3 October 2007|publisher=[[SETI Institute]]| archiveurl=http://web.archive.org/web/20071103094424/http://www.seti.org/about-us/voices/phillips-080503.php| archivedate = 3 November 2007}}</ref>
 
During the encounter, signals from the spacecraft required 246&nbsp;minutes to reach Earth. Hence, for the most part, the ''Voyager 2'' mission relied on preloaded commands for the Neptune encounter. The spacecraft performed a near-encounter with the moon [[Nereid (moon)|Nereid]] before it came within 4400&nbsp;km of Neptune's atmosphere on 25 August, then passed close to the planet's largest moon [[Triton (moon)|Triton]] later the same day.<ref name=burgess>[[#Burgess|Burgess]] (1991):46–55.</ref>
 
The spacecraft verified the existence of a magnetic field surrounding the planet and discovered that the field was offset from the centre and tilted in a manner similar to the field around Uranus. The question of the planet's rotation period was settled using measurements of radio emissions. ''Voyager 2'' also showed that Neptune had a surprisingly active weather system. Six new moons were discovered, and the planet was shown to have more than one ring.<ref name="science4936" /><ref name=burgess/>
 
In 2003, there was a proposal in [[NASA]]'s "Vision Missions Studies" for a "[[Neptune Orbiter|Neptune Orbiter with Probes]]" mission that does ''[[Cassini–Huygens|Cassini]]''-level science. The work is being done in conjunction with [[Jet Propulsion Laboratory|JPL]] and the [[California Institute of Technology]].<ref>{{cite journal
|last=Spilker|first=T. R.|coauthors=Ingersoll, A. P.
|title=Outstanding Science in the Neptune System From an Aerocaptured Vision Mission
|journal=Bulletin of the American Astronomical Society
|year=2004|volume=36|page=1094
|bibcode=2004DPS....36.1412S
|last2=Ingersoll}}</ref> Another, more recent proposal was for [[Argo (spacecraft)|Argo]], a flyby spacecraft that would visit [[Jupiter]], [[Saturn]], Neptune, and a [[Kuiper belt object]].<ref name=argho1/> However, the focus would be on Neptune and its largest moon [[Triton (moon)|Triton]] to help plug a predicted 50-year gap in exploration of the system.<ref name=argho1/><ref name=argho1>[http://www.spacepolicyonline.com/pages/images/stories/PSDS%20GP1%20Hansen_Argo_Neptune%20Mission%20Concept.pdf Argo - A Voyage Through the Outer Solar System ]</ref> [[New Horizons 2]] might have also done a flyby.
{{-}}
-->
 
==Βλέπε επίσης==
{{Portal|Solar System}}
{{Wikipedia books
| 1 = Neptune
| 3 = Solar System
}}
* [[Hot Neptune]]
* [[Planets in astrology#Neptune|Neptune in astrology]]
* [[Neptune in fiction]]
* [[Neptunium]]
* ''[[The Planets|Neptune, the Mystic]]'' – one of the seven movements in [[Gustav Holst]]'s ''Planets'' suite
 
==Notes==
{{reflist|group=lower-alpha}}
 
==References==
{{reflist
| colwidth = 30em
| refs =
<ref name="Encrenaz 2003">
{{cite doi|10.1016/S0032-0633(02)00145-9}}
</ref>
 
<ref name="Herbert & Sandel 1999">
{{cite doi|10.1016/S0032-0633(98)00142-1}}
</ref>
 
<ref name="Lunine 1993">
{{cite doi|10.1146/annurev.aa.31.090193.001245}}
</ref>
 
<ref name="Podolak Weizman et al. 1995">
{{cite doi|10.1016/0032-0633(95)00061-5}}
</ref>
 
<ref name="Seidelmann Archinal A'hearn et al. 2007">
{{cite doi|10.1007/s10569-007-9072-y}}
</ref>
 
<ref name="Unsöld & Baschek 2001">
{{cite book
| last1 = Unsöld
| first1 = Albrecht
| last2 = Baschek
| first2 = Bodo
| year = 2001
| title = The New Cosmos: An Introduction to Astronomy and Astrophysics
| edition = 5th
| publisher = Springer
| page = 47
| isbn = 978-3-540-67877-9
}} See Table 3.1.
</ref>
}}
 
==Bibliography==
* {{cite book|ref=Burgess
| last = Burgess|first=Eric|year=1991
| title = Far Encounter: The Neptune System
| publisher = [[Columbia University Press]]|isbn = 978-0-231-07412-4}}
* {{cite book|ref=Moore
| last = Moore|first=Patrick|authorlink=Patrick Moore
| title = The Data Book of Astronomy|year=2000
| publisher = [[CRC Press]]|isbn = 978-0-7503-0620-1}}
 
==Further reading==
* {{cite book
| last = Miner|first=Ellis D.|coauthors=Wessen, Randii R.
| title = Neptune: The Planet, Rings, and Satellites
| year = 2002|publisher=Springer-Verlag
| isbn = 978-1-85233-216-7}}
* {{cite book
| last = Standage|first=Tom
| title = The Neptune File|year=2001
| publisher = Penguin
| isbn = 978-0-8027-1363-6}}
 
Τα ονόματα των δορυφόρων είναι τα εξής: [[Ναϊάδα (δορυφόρος)|Ναϊάδα]], [[Θάλασσα (δορυφόρος)|Θάλασσα]], [[Δέσποινα (δορυφόρος)|Δέσποινα]], [[Γαλάτεια (δορυφόρος)|Γαλάτεια]], [[Λάρισσα (δορυφόρος)|Λάρισσα]], [[Πρωτέας (δορυφόρος)|Πρωτέας]], [[Τρίτωνας (δορυφόρος)|Τρίτωνας]], [[Νηρηίδα (δορυφόρος)|Νηρηίδα]], [[Αλιμήδη (δορυφόρος)|Αλιμήδη]], [[Σαώ (δορυφόρος)|Σαώ]], [[Λαομέδεια (δορυφόρος)|Λαομέδεια]], [[Ψαμάθη (δορυφόρος)|Ψαμάθη]], [[Νησώ (δορυφόρος)|Νησώ]] και [[S/2004 N 1]].
==External links==
{{Sister project links|Neptune}}
* [http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html NASA's Neptune fact sheet]
* [http://www.nineplanets.org/neptune.html Neptune] from Bill Arnett's nineplanets.org
* [http://www.astronomycast.com/astronomy/episode-63-neptune/ Neptune] [[Astronomy Cast]] episode No. 63, includes full transcript.
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune Neptune Profile] at [http://solarsystem.nasa.gov NASA's Solar System Exploration site]
* [http://www.projectshum.org/Planets/neptune.html Planets&nbsp;– Neptune] A children's guide to Neptune.
* {{cite web|last=Merrifield|first=Michael|title=Neptune|url=http://www.sixtysymbols.com/videos/neptune.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]|coauthors=Bauer, Amanda|year=2010}}
*[http://www.planetary.org/blogs/guest-blogs/2013/neptune-the-new-amateur-boundary.html Neptune by amateur] (The Planetary Society)
 
== Εξερεύνηση ==
Ο Ποσειδώνας έχει εξερευνηθεί έως σήμερα μόνο από μία διαστημική αποστολή, το [[Βόγιατζερ 2]], που πέρασε σε απόσταση 4.500 περίπου χιλιομέτρων από τις κορυφές των νεφών του πλανήτη στις [[25 Αυγούστου]] [[1989]].<ref name=burgess>Burgess (1991):46–55.</ref> Ενώ οι επιστήμονες περίμεναν ότι θα συναντούσαν έναν πλανήτη με ήρεμη ατμόσφαιρα, όπως ο [[Ουρανός (πλανήτης)|Ουρανός]], επειδή η [[ηλιακή ακτινοβολία]] που φτάνει στο εξωτερικό ηλιακό σύστημα είναι ελάχιστη, το Βόγιατζερ τους διέψευσε, αποκαλύπτοντας έναν πλανήτη με τους πιο γρήγορους ανέμους στο ηλιακό σύστημα, μα και με μια [[Μεγάλη Σκοτεινή Κηλίδα|κηλίδα]] στην ατμόσφαιρα, μία μεγάλη ατμοσφαιρική [[καταιγίδα]] δηλαδή, αντάξια του μεγέθους της Μεγάλης Κόκκινης Κηλίδας του Δία, κατ' αναλογία με το μικρότερο μέγεθος του Ποσειδώνα. Το Βόγιατζερ επιβεβαίωσε επίσης την ύπαρξη των δακτυλίων του πλανήτη και φωτογράφισε τους δορυφόρους του και ιδιαίτερα τον [[Τρίτωνας (δορυφόρος)|Τρίτωνα]], ανακαλύπτοντας στην επιφάνειά του [[κρυοηφαίστειο|κρυοηφαίστεια]] που εκτινάσσουν πίδακες παγωμένου [[άζωτο|αζώτου]].
 
Κατά τη δεκαετία του '90 υπήρχαν θεωρητικά σχέδια για επιπλέον αποστολές στον Ποσειδώνα, όμως ακυρώθηκαν. Σήμερα (2012) δεν υπάρχουν άμεσα σχέδια για την αποστολή κάποιας διαστημοσυσκευής στον πλανήτη.
 
== Παραπομπές ==
{{reflist|2}}
 
== Εξωτερικοί σύνδεσμοι ==
{{commonscat|Neptune (planet)}}
* [http://www.astronomy.gr/main.cfm?module=educational&section=enc_as&en_id=24&do=detail Ποσειδώνας:ο πιο μακρινός γίγαντας πλανήτης], Πλανητάριο Θεσσαλονίκης.
* [http://www.kathimerini.gr/4dcgi/_w_articles_kathglobal_2_20/02/2005_1283790 Ο άλλος γαλάζιος πλανήτης], Π. Νιάρχος, ''Καθημερινή'' 20 Φεβρουαρίου 2005.
 
{{Πύλη|Αστρονομία|P space.png}}
Ανακτήθηκε από "https://el.wikipedia.org/wiki/Ποσειδώνας_(πλανήτης)"