Triton (moon)

William Lassell, the discoverer of Triton
The orbit of Triton (red) is opposite in direction and tilted −23° compared to a typical moon's orbit (green) in the plane of Neptune's equator.
Animation of Triton
The Kuiper belt (green), in the Solar System's outskirts, is where Triton is thought to have originated.
Artist's impression of Triton, showing its tenuous atmosphere just over the limb.
Clouds observed above Triton's limb by Voyager 2.
Interpretative geomorphological map of Triton
Triton's bright south polar cap above a region of cantaloupe terrain
Cantaloupe terrain viewed from 130,000 km by Voyager 2, with crosscutting Europa-like double ridges. Slidr Sulci (vertical) and Tano Sulci form the prominent "X".
Tuonela Planitia (left) and Ruach Planitia (center) are two of Triton's cryovolcanic "walled plains". The paucity of craters is evidence of extensive, relatively recent, geologic activity.
NASA illustration detailing the studies of the proposed Trident mission
Neptune (top) and Triton (bottom) three days after flyby of Voyager 2
thumb|Close up of the volcanic province of Leviathan Patera, the caldera in the center of the image. Several pit chains extend radially from the caldera to the right of the image, while the smaller of the two cryolava lakes is seen to the upper left. Just off-screen to the lower left is a fault zone aligned radially with the caldera, indicating a close connection between the tectonics and volcanology of this geologic unit.
thumb|Dark streaks across Triton's south polar cap surface, thought to be dust deposits left by eruptions of nitrogen geysers
thumb|Two large cryolava lakes on Triton, seen west of Leviathan Patera. Combined, they are nearly the size of Kraken Mare on Titan. These features are unusually crater free, indicating they are young and were recently molten.

Largest natural satellite of the planet Neptune, and was the first Neptunian moon to be discovered, on October 10, 1846, by English astronomer William Lassell.

- Triton (moon)

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Photograph taken by NASA's Voyager 2 in 1989

Neptune

Eighth and farthest-known Solar planet from the Sun.

Eighth and farthest-known Solar planet from the Sun.

Photograph taken by NASA's Voyager 2 in 1989
♆
Galileo Galilei
Urbain Le Verrier
A size comparison of Neptune and Earth
Combined colour and near-infrared image of Neptune, showing bands of methane in its atmosphere, and four of its moons, Proteus, Larissa, Galatea, and Despina
Bands of high-altitude clouds cast shadows on Neptune's lower cloud deck.
The Great Dark Spot (top), Scooter (middle white cloud), and the Small Dark Spot (bottom), with contrast exaggerated.
Four images taken a few hours apart with the NASA/ESA Hubble Space Telescope Wide Field Camera 3
Neptune (red arc) completes one orbit around the Sun (centre) for every 164.79 orbits of Earth. The light blue object represents Uranus.
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 belt" (cubewanos), and the 1:2 resonance (twotinos).
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
Natural-colour view of Neptune with Proteus (top), Larissa (lower right), and Despina (left), from the Hubble Space Telescope
Neptune's moon Proteus
A composite Hubble image showing Hippocamp with other previously discovered inner moons in Neptune's ring system
Neptune's rings
In 2018, the European Southern Observatory developed unique laser-based methods to get clear and high-resolution images of Neptune from the surface of Earth.
A Voyager 2 mosaic of Triton
The appearance of a Northern Great Dark Spot in 2018 is evidence of a huge storm brewing.<ref>{{cite web |title=A storm is coming |url=https://www.spacetelescope.org/images/potw1907a/ |website=spacetelescope.org |access-date=19 February 2019 |language=en |archive-url=https://web.archive.org/web/20190220062857/https://www.spacetelescope.org/images/potw1907a/ |archive-date=20 February 2019 |url-status=live }}</ref>
The Northern Great Dark Spot and a smaller companion storm imaged by Hubble in 2020<ref>{{cite web|url=https://hubblesite.org/contents/news-releases/2020/news-2020-59.html|title=Dark Storm on Neptune Reverses Direction, Possibly Shedding Fragment|author1=Michael H. Wong|author2=Amy Simon|publisher=Hubblesite|date=15 December 2020|access-date=25 December 2020|archive-date=25 December 2020|archive-url=https://web.archive.org/web/20201225153808/https://hubblesite.org/contents/news-releases/2020/news-2020-59.html|url-status=live}}</ref>
The Great Dark Spot, as imaged by Voyager 2
Neptune's shrinking vortex<ref>{{cite web|title=Neptune's shrinking vortex|url=http://www.spacetelescope.org/images/potw1808a/|website=spacetelescope.org|access-date=19 February 2018|archive-url=https://web.archive.org/web/20180219125043/http://www.spacetelescope.org/images/potw1808a/|archive-date=19 February 2018|url-status=live}}</ref>

Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 13 known moons were located telescopically until the 20th century.

Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black)

Retrograde and prograde motion

Object in the direction opposite the rotation of its primary, that is, the central object .

Object in the direction opposite the rotation of its primary, that is, the central object .

Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black)
The orange moon is in a retrograde orbit.

Retrograde satellites are generally small and distant from their planets, except Neptune's satellite Triton, which is large and close.

Neptune (top) and Triton (bottom), three days after the Voyager 2 flyby in 1989

Moons of Neptune

The planet Neptune has 14 known moons, which are named for minor water deities in Greek mythology.

The planet Neptune has 14 known moons, which are named for minor water deities in Greek mythology.

Neptune (top) and Triton (bottom), three days after the Voyager 2 flyby in 1989
The number of moons known for each of the four outer planets up to October 2019. Neptune currently has 14 known satellites.
Orbit diagram of Neptune's inner moons including Triton, with their names and orbit directions indicated
Size comparison of Neptune's seven inner moons
The orbit of Triton (red) is different from most moons' orbit (green) in the orbit's direction, and the orbit is tilted −23°.
The diagram illustrates the orbits of Neptune's irregular moons excluding Triton. The eccentricity is represented by the yellow segments extending from the pericenter to apocenter with the inclination represented on Y axis. The moons above the X axis are prograde, those beneath are retrograde. The X axis is labeled in Gm and the fraction of the Hill sphere's radius.
The relative masses of the Neptunian moons

By far the largest of them is Triton, discovered by William Lassell on October 10, 1846, 17 days after the discovery of Neptune itself; over a century passed before the discovery of the second natural satellite, Nereid.

The internal structure of Earth

Mantle (geology)

Layer inside a planetary body bounded below by a core and above by a crust.

Layer inside a planetary body bounded below by a core and above by a crust.

The internal structure of Earth

Titan and Triton each have a mantle made of ice or other solid volatile substances.

The planet Mars has an atmosphere composed of thin layers of gases.

Atmosphere

Layer of gas or layers of gases that envelope a planet, and is held in place by the gravity of the planetary body.

Layer of gas or layers of gases that envelope a planet, and is held in place by the gravity of the planetary body.

The planet Mars has an atmosphere composed of thin layers of gases.
The atmospheric gases around Earth scatter blue light (shorter wavelengths) more than light toward the red end (longer wavelengths) of the visible spectrum; thus, a blue glow over the horizon is seen when observing Earth from outer space.
A diagram of the layers of Earth's atmosphere
Graphs of escape velocity against surface temperature of some Solar System objects showing which gases are retained. The objects are drawn to scale, and their data points are at the black dots in the middle.

Titan, a moon of Saturn, and Triton, a moon of Neptune, have atmospheres mainly of nitrogen.

William Lassell

English merchant and astronomer.

English merchant and astronomer.

In 1846, Lassell discovered Triton, the largest moon of Neptune, just 17 days after the discovery of Neptune itself by German astronomer Johann Gottfried Galle, using his self-built instrument.

Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense haze.

Titan (moon)

Largest moon of Saturn and the second-largest natural satellite in the Solar System.

Largest moon of Saturn and the second-largest natural satellite in the Solar System.

Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense haze.
Christiaan Huygens discovered Titan in 1655.
Titan's orbit (highlighted in red) among the other large inner moons of Saturn. The moons outside its orbit are (from the outside to the inside) Iapetus and Hyperion; those inside are Rhea, Dione, Tethys, Enceladus, and Mimas.
True-color image of layers of haze in Titan's atmosphere
Trace organic gases in Titan's atmosphere—HNC (left) and HC3N (right).
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Methane clouds (animated; July 2014).
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False-color Cassini radar mosaic of Titan's north polar region. Blue coloring indicates low radar reflectivity, caused by hydrocarbon seas, lakes and tributary networks filled with liquid ethane, methane and dissolved . About half of the large body at lower left, Kraken Mare, is shown. Ligeia Mare is at lower right.
Mosaic of three Huygens images of channel system on Titan
Rimmed lakes of Titan (artist concept)
Near-infrared radiation from the Sun reflecting off Titan's hydrocarbon seas
Radar image of a 139 km-diameter impact crater on Titan's surface, showing a smooth floor, rugged rim, and possibly a central peak.
Ligeia Mare – SAR and clearer despeckled views.
Near-infrared image of Tortola Facula, thought to be a possible cryovolcano
False-color VIMS image of the possible cryovolcano Sotra Patera, combined with a 3D map based on radar data, showing 1000-meter-high peaks and a 1500-meter-deep crater.
Sand dunes in the Namib Desert on Earth (top), compared with dunes in Belet on Titan
Titan - three dust storms detected in 2009–2010.
Voyager 1 view of haze on Titan's limb (1980)
Cassini's Titan flyby radio signal studies (artist's concept)
The balloon proposed for the Titan Saturn System Mission (artistic rendition)
Global map of Titan – with IAU labels (August 2016).
Titan – infrared views (2004–2017)
Titan's North Pole (2014)
Titan's South Pole (2014)

It is second in terms of relative diameter of moons to a gas giant; Titan being 1/22.609 of Saturn's diameter, Triton is larger in diameter relative to Neptune at 1/18.092.

Elliptic orbit by eccentricity ····

Orbital eccentricity

Kepler orbits.svg:

Kepler orbits.svg:

Elliptic orbit by eccentricity ····
Plot of the changing orbital eccentricity of Mercury, Venus, Earth, and Mars over the next years. The arrows indicate the different scales used, as the eccentricities of Mercury and Mars are much greater than those of Venus and Earth. The 0 point on this plot is the year 2007.

Neptune's largest moon Triton has an eccentricity of 0 (0), the smallest eccentricity of any known moon in the Solar System; its orbit is as close to a perfect circle as can be currently measured.

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan

Cryovolcano

Type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point.

Type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point.

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan
Plumes of Enceladus, feeding Saturn's E Ring, seem to arise from the "Tiger Stripes" near the south pole.

In addition, although they are not known to form volcanoes, ice geysers have been observed on Enceladus and potentially Triton.

Irregular satellites of Jupiter (red), Saturn (yellow), Uranus (green) and Neptune (blue) (excluding Triton). The horizontal axis shows their distance from the planet (semi-major axis) expressed as a fraction of the planet's Hill sphere's radius. The vertical axis shows their orbital inclination. Points or circles represent their relative sizes. Data as of August 2006.

Irregular moon

Irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit.

Irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit.

Irregular satellites of Jupiter (red), Saturn (yellow), Uranus (green) and Neptune (blue) (excluding Triton). The horizontal axis shows their distance from the planet (semi-major axis) expressed as a fraction of the planet's Hill sphere's radius. The vertical axis shows their orbital inclination. Points or circles represent their relative sizes. Data as of August 2006.
Phoebe, Saturn's largest irregular satellite
The power law for the size distribution of objects in the Kuiper belt, where q ≈ 4 and thus N ~ D−3. That is, for every Kuiper beld object of a particular size, there are approximately 8 times as many objects half that size and a thousands times as many objects one-tenth that size.
This diagram illustrates the differences of colour in the irregular satellites of Jupiter (red labels), Saturn (yellow) and Uranus (green). Only irregulars with known colour indices are shown. For reference, the centaur Pholus and three classical Kuiper belt objects are also plotted (grey labels, size not to scale).
For comparison, see also colours of centaurs and KBOs.
The orbits of Jupiter's irregular satellites, showing how they cluster into groups. Satellites are represented by circles that indicate their relative sizes. An object's position on the horizontal axis shows its distance from Jupiter. Its position on the vertical axis indicates its orbital inclination. The yellow lines indicate its orbital eccentricity (i.e. the extent to which its distance from Jupiter varies during its orbit).
Animation of Himalia's orbit. ··
Irregular satellites of Saturn, showing how they cluster into groups. For explanation, see Jupiter diagram
Irregular satellites of Uranus (green) and Neptune (blue) (excluding Triton). For explanation, see Jupiter diagram
Distant Cassini image of Himalia
Animation of Saturn's Inuit group of satellites {{legend2|RoyalBlue| Kiviuq}}{{·}}{{legend2|Lime| Ijiraq}}{{·}}{{legend2|Gold| Paaliaq}}{{·}}{{legend2|OrangeRed| Siarnaq}}{{·}}{{legend2|Cyan|Tarqeq}}
Animation of Phoebe's orbit. {{legend2|RoyalBlue| Saturn}}{{·}}{{legend2| Magenta | Phoebe}}{{·}}{{legend2|Cyan|Titan}}
71 irregular moons of Jupiter (with Callisto for comparison)
58 irregular moons of Saturn (with Iapetus for comparison)
9 irregular moons of Uranus
6 irregular moons of Neptune (excluding Triton)

The term does not refer to shape as Triton is a round moon, but is considered irregular due to its orbit.