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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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 James Webb Space Telescope launched in December 2021. By the time it launched, JWST cost about US$10 billion.

Large strategic science missions

NASA's large strategic science missions or large strategic missions, formerly known as Flagship missions or Flagship-class missions, are the costliest and most capable NASA science spacecraft.

NASA's large strategic science missions or large strategic missions, formerly known as Flagship missions or Flagship-class missions, are the costliest and most capable NASA science spacecraft.

The James Webb Space Telescope launched in December 2021. By the time it launched, JWST cost about US$10 billion.

The targets of Flagship missions may include complex missions to the atmosphere and surface of Venus, the lower atmosphere and surface of Titan, the surface and subsurface of Europa, the stormy atmosphere of Jupiter, the dusty surface of Mars, the ring systems of Saturn, the deep atmospheres of the ice giants Neptune and Uranus, the surface of the moon Triton, the plumes of Enceladus, the surface and magnetosphere of Mercury, and the surface of a comet nucleus in the form of cryogenically preserved samples.

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.

A cross-section of a geyser in action

Geyser

Spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam.

Spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam.

A cross-section of a geyser in action
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Hyperthermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park
Distribution of major geysers in the world.
The geyser Strokkur in Iceland – a tourist spot.

Water vapor jets have been observed near the south pole of Saturn's moon Enceladus, while nitrogen eruptions have been observed on Neptune's moon Triton.

New Horizons color composite image of 486958 Arrokoth showing its red color from tholins on its surface

Tholin

Tholins (after the Greek θολός (tholós) "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide, methane or ethane , often in combination with nitrogen or water.

Tholins (after the Greek θολός (tholós) "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide, methane or ethane , often in combination with nitrogen or water.

New Horizons color composite image of 486958 Arrokoth showing its red color from tholins on its surface
Polyacrylonitrile, one hypothesized polymeric component of tholins, mostly in chemically degraded form as polymers containing nitrile and amino groups. It is used experimentally to create tholin mixtures.
The formation of tholins in the atmosphere of Titan
The surface of Titan as viewed from the Huygens lander. Tholins are suspected to be the source of the reddish color of both the surface and the atmospheric haze.
Linear fractures on Europa's surface, likely colored by tholins.
The trailing hemisphere of Saturn's moon Rhea is covered with tholins.
Close-up view of Sputnik Planitia on Pluto as viewed by the New Horizons spacecraft, showing nitrogen ice glaciers and reddish-colored tholins.

Neptune's moon Triton is observed to have the reddish color characteristic of tholins.

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.

Cassini image of Phoebe

Phoebe (moon)

Irregular satellite of Saturn with a mean diameter of 213 km. It was discovered by William Henry Pickering on March 18, 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Station of the Carmen Alto Observatory near Arequipa, Peru, by DeLisle Stewart.

Irregular satellite of Saturn with a mean diameter of 213 km. It was discovered by William Henry Pickering on March 18, 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Station of the Carmen Alto Observatory near Arequipa, Peru, by DeLisle Stewart.

Cassini image of Phoebe
Animation of Phoebe's orbit.
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Artist's impression of the Phoebe ring, which dwarfs the main rings
Cassini closeup of Phoebe from 13 June 2004; the crater Euphemus is at top center
Named craters on Phoebe
Phoebe (with NGC 4179 in the lower right corner) as imaged with a 24" telescope
Map of Phoebe's middle latitudes. The higher latitudes have been clipped from the main map, but can be seen in the polar projections.
Map of Phoebe's south polar region
Map of Phoebe's north polar region
3D map showing Phoebe's once spherical shape

Phoebe is the second largest retrograde satellite in the Solar System after Triton.

The scheme of Neptune's ring-moon system. Solid lines denote rings; dashed lines denote orbits of moons.

Rings of Neptune

Observing program proposed by André Brahic and Bruno Sicardy from Paris Observatory, and at Cerro Tololo Interamerican Observatory by F. Vilas and L.-R.

Observing program proposed by André Brahic and Bruno Sicardy from Paris Observatory, and at Cerro Tololo Interamerican Observatory by F. Vilas and L.-R.

The scheme of Neptune's ring-moon system. Solid lines denote rings; dashed lines denote orbits of moons.
A pair of Voyager 2 images of Neptune's ring system
A Voyager ring image shown at increased brightness to bring out fainter features
Arcs in the Adams ring (left to right: Fraternité, Égalité, Liberté), plus the Le Verrier ring on the inside

The first mention of rings around Neptune dates back to 1846 when William Lassell, the discoverer of Neptune's largest moon, Triton, thought he had seen a ring around the planet.

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.