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Encyclopedia > Neptune's natural satellites
Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby.
Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby.

Neptune has thirteen known moons. The largest by far is Triton, discovered by William Lassell just seventeen days after the discovery of Neptune itself. It took about one hundred years to discover the second, Nereid. Image File history File links Voyager_2_Neptune_and_Triton. ... Image File history File links Voyager_2_Neptune_and_Triton. ... Adjectives: Neptunian Atmosphere Surface pressure: (?)≫(?) 100 kPa : is asked the pressure at the cloud level. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... William Lassell (June 18, 1799 – October 5, 1880) was a British astronomer, born in Bolton, Lancashire, England. ... Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ...

Contents

Unusual orbits

Triton orbits Neptune on a circular but retrograde orbit. While retrograde orbits are common among distant irregular satellites, Triton is a unique case of retrograde moon so close to its planet. Direct motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called prograde motion. ...


The third largest moon of Neptune, Nereid follows a prograde but the most eccentric orbit among the moons of the solar system, being at its apocenter more than seven times further from the planet than at its pericenter. Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ... (This page refers to eccitricity in astrodynamics. ... A diagram of Keplerian orbital elements. ...


Two natural satellites discovered in 2002 and 2003, Psamathe and Neso, have the largest orbits of any natural satellites discovered in the Solar system to date. They take 25 years to orbit Neptune at an average of 125 times the distance between Earth and the Moon. For album titles with the same name, see 2002 (album). ... 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Psamathe (sam-a-thee, Greek Ψαμαθεια, Latin Psamathē) is an irregular natural satellite of Neptune. ... Neso, also known as Neptune XIII, is the outermost irregular natural satellite of Neptune. ...


Theories of origin

It is likely that Neptune's inner satellites are not the original bodies that formed with Neptune but accreted rubble from the havoc that was wreaked after Triton's capture. Triton's original captured orbit would have been highly eccentric, and caused chaotic perturbations in the orbits of the original inner Neptunian satellites, caussing them to collide and become reduced to a rubble disc. Only after Triton's orbit became circularised did some of the rubble disc re-accrete into the present-day satellites [1]. Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ...


The mechanism of the Triton’s capture have been the subject of a few theories over the years. The most recent postulates that Triton was captured in a three body encounter. In this scenario, Triton is the surviving member of a binary object1 disrupted by the encounter with Neptune.[2].


Numerical simulations show that another moon discovered in 2002, Halimede has had a high probability of collision with Nereid during the lifespan of the system.[3] As both moons appear to have similar (grey) colours, the satellite could be a fragment of Nereid.[4] Halimede is a retrograde irregular satellite of Neptune. ...


1Binary objects, gravitational association of two objects, are quite common among Trans-Neptunian Objects (>10%; the most known is Pluto -Charon) and less so among the asteroids (e.g. Ida and Dactyl). A trans-Neptunian object (TNO) is any object in the solar system with all or most of its orbit beyond that of Neptune. ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... Charon (shair-ən or kair-ən (key), IPA , Greek Χάρων), discovered in 1978, is, depending on the definition employed, either the largest moon of Pluto or one member of a double dwarf planet with Pluto being the other member. ... It has been suggested that minor planet be merged into this article or section. ... NASA image of 243 Ida. ... 243 Ida (left) and Dactyl (right), as photographed by the Galileo spacecraft. ...


The natural satellites

The Neptunian moons are listed here by orbital period, from shortest to longest. Triton, which is not only massive enough for its surface to have collapsed into a spheroid, but is comparable in size to our own moon, is highlighted in purple. Irregular (captured) moons are shown in grey; prograde in light grey and retrograde in dark grey. (Triton is also thought to be captured.) This article or section does not cite its references or sources. ... In mathematics, a spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ...

Order Name (spheroidal moon in bold)

(Pronunciation key) This chart shows concisely the most common way in which the International Phonetic Alphabet (IPA) is applied to represent the English language. ...

Image Diameter (km) Mass
(1016 kg)
Semi-major axis (km) Orbital period (d) Inclination (°) to Neptune's Equator Discovery Date
1 Neptune III Naiad ˈnaɪ.əd 67 (96×60×52) ~19 48,227 0.294 4.7° 1989
2 Neptune IV Thalassa θəˈlæs.ə 83 (108×100×52) ~35 50,075 0.311 0.2° 1989
3 Neptune V Despina dɛsˈpi.nə 152 (180×150×130) ~210 52,526 0.335 0.1° 1989
4 Neptune VI Galatea ˌgæl.əˈti.ə 175 (204×184×144) 212 61,953 0.429 0.1° 1989
5 Neptune VII Larissa ləˈrɪs.ə 195 (216×204×164) ~420 73,548 0.555 0.2° 1989
6 Neptune VIII Proteus ˈproʊ.ti.əs 418 (436 × 416 × 402) ~5,000 117,647 1.122 0.6° 1989
7 Neptune I Triton ˈtraɪ.tən 2707 2,140,000 354,800 −5.877 156.8° 1846
8 Neptune II Nereid ˈnɪr.i.ɨd
340 ~3,100 5,513,400 360.14 27.6° 1949
9 Neptune IX Halimede ˌhæl.əˈmi.di 60 ~9 15,728,000 −1879.71 2002
10 Neptune XI Sao ˈseɪ.oʊ 38 ~9 22,422,000 2914.07 2002
11 Neptune XII Laomedeia ˌleɪ.ə.məˈdi.ə 38 ~9 23,571,000 3167.85 2002
12 Neptune X Psamathe ˈsæm.ə.θi 28 ~1.5 46,695,000 −9115.91 2002
13 Neptune XIII Neso ˈni.soʊ 60 ~9 48,387,000
(0.32 AU)
−9373.99 2003

Negative orbital periods indicate a retrograde orbit around Neptune (opposite to the planet's rotation) A simulated view of Naiad orbiting Neptune with The Sun in the distance. ... A simulated view of Thalassa orbiting Neptune. ... A simulated view of Despina orbiting Neptune Despina (des-pee-na or des-pye-na; Latin DespÅ“na from Greek Δεσποίνη) is the third known moon of Neptune. ... Image File history File links No higher resolution available. ... A simulated view of Galatea orbiting Neptune Galatea (gal-a-tee-a, Greek Γαλατεία) is the fourth known moon of Neptune, named after Galatea, one of the Nereids of Greek legend. ... A simulated view of Larissa orbiting Neptune Larissa (la-ris-a, Greek Λάρῑσα) is the fifth of Neptunes known moons. ... Image File history File links Larissa_1. ... Atmospheric pressure 0 kPa Proteus (proe-tee-us, Greek Πρωτέας) is one of Neptunes moons. ... Download high resolution version (727x726, 31 KB)Photo of Netptunes satellite Proteus taken by Voyager 2 (large version). ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Download high resolution version (1024x796, 150 KB)A color mosaic of Triton, Neptunes moon (large). ... Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ... Original caption: Nereid, the last satellite of Neptune to be discovered before Voyagers recent discoveries, was first seen by Gerard Kuiper in 1949. ... Halimede is a retrograde irregular satellite of Neptune. ... Sao is a prograde irregular satellite of Neptune. ... Laomedeia, or Neptune XII, is a prograde irregular satellite of Neptune. ... Psamathe (sam-a-thee, Greek Ψαμαθεια, Latin PsamathÄ“) is an irregular natural satellite of Neptune. ... Neso, also known as Neptune XIII, is the outermost irregular natural satellite of Neptune. ... The astronomical unit (AU or au or a. ... This article is about retrograde motion. ...


Irregular satellites

Neptune's irregular satellites.
Neptune's irregular satellites.

The diagram illustrates the orbits of Neptune’s irregular satellites discovered so far. The eccentricity of the orbits is represented by the yellow segments (extending from the pericentre to the apocentre) with the inclination represented on Y axis. The satellites above the X axis are prograde, the satellites beneath are retrograde. The X axis is labelled in Gm (million km) and the fraction of the Hill sphere's (gravitational influence) radius (~116 Gm for Neptune). Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... This diagram shows the orbits of Saturns irregular satellites surrounding the planet like a swarm. ... A diagram of Keplerian orbital elements. ... This article is about retrograde motion. ... Prograde motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called direct motion, especially in astrology. ... A gigametre (American spelling: gigameter) (symbol: Gm) is a unit of length equal to 109 metres. ... A Hill sphere approximates the gravitational sphere of influence of one astronomical body in the face of perturbations from another heavier body around which it orbits. ...


Given the similarity of their orbits, it was suggested that Neso and Psamathe could have a common origin in the break-up of a larger moon.[5] Neso, also known as Neptune XIII, is the outermost irregular natural satellite of Neptune. ... Psamathe (sam-a-thee, Greek Ψαμαθεια, Latin Psamathē) is an irregular natural satellite of Neptune. ...


Triton, the biggest moon following a retrograde but a quasi-circular orbit, also conjectured to be a captured satellite, is not shown. Nereid, on a prograde but very eccentric orbit is believed to be scattered during Triton's capture.[6]


Naming notes

Some asteroids share the same names as moons of Neptune: 74 Galatea, 1162 Larissa. See also Name conflicts of solar system objects. It has been suggested that minor planet be merged into this article or section. ... 74 Galatea (gal-a-tee-a) is a large Main belt asteroid. ... Although in principle every named body in the Solar system ought to have a distinct name, due to a variety of circumstances, there are several real or apparent name conflicts between different solar system bodies. ...


Note that Triton did not have an official name until the twentieth century. Although the name was suggested in 1880 by Camille Flammarion, it did not come into common use until at least the 1930s. Usually, it was simply known as "the satellite of Neptune" (the second satellite, Nereid, was not discovered until 1949). (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999... Year 1880 (MDCCCLXXX) was a leap year starting on Thursday (link will display the full calendar). ... Camille Flammarion Camille Flammarion (February 26, 1842 – June 3, 1925) was a French astronomer and author. ... 1930 (MCMXXX) was a common year starting on Wednesday (link is to a full 1930 calendar). ... Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ... 1949 (MCMXLIX) was a common year starting on Saturday (the link is to a full 1949 calendar). ...


References

  1. ^ D. Banfield and N. Murray (1992). "A dynamical history of the inner Neptunian satellites". Icarus 99: 390. 
  2. ^ C.B. Agnor & D.P. Hamilton Neptune's capture of its moon Triton in a binary-planet gravitational encounter, Nature, 441 (2006), pp. 192. (pdf)
  3. ^ M.Holman, JJ Kavelaars, B.Gladman, T.Grav, W.Fraser, D.Milisavljevic, P.Nicholson, J.Burns, V.Carruba, J-M.Petit, P.Rousselot, O.Mousis, B.Marsden, R.Jacobson Discovery of five irregular moons of Neptune, Nature, 430 (2004), pp. 865-867. Final preprint(pdf)
  4. ^ T.Grav, M.Holman and W.Fraser, Photometry of Irregular Satellites of Uranus and Neptune, The Astrophysical Journal, 613 (2004), pp.L77–L80 (preprint)
  5. ^ Scott S. Sheppard, David C. Jewitt, Jan Kleyna, A Survey for "Normal" Irregular Satellites Around Neptune: Limits to Completeness (preprint)
  6. ^ Goldreich, P.; Murray, N.; Longaretti, P. Y.; Banfield, D. Neptune's story, Science, 245, (1989), p. 500-504.
 v  d  e The Solar System
The Sun Mercury Venus The Moon Earth Phobos and Deimos Mars Ceres The asteroid belt Jupiter Jupiter's natural satellites Saturn Saturn's natural satellites Uranus Uranus' natural satellites Neptune's natural satellites Neptune Charon, Nix, and Hydra Pluto The Kuiper belt Dysnomia Eris The scattered disc The Oort cloud
The Sun · Mercury · Venus · Earth · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Eris
Planets · Dwarf planets · Moons: Terrestrial · Martian · Asteroidal · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian
Small bodies:   Meteoroids · Asteroids (Asteroid belt) · Centaurs · TNOs (Kuiper belt/Scattered disc) · Comets (Oort cloud)
See also astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Solar System Portal

  Results from FactBites:
 
NationMaster - Encyclopedia: Triton (moon) (6369 words)
Halimede is a retrograde irregular satellite of Neptune.
Sao is a prograde irregular satellite of Neptune.
Laomedeia, or Neptune XII, is a prograde irregular satellite of Neptune.
  More results at FactBites »

 
 

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