Triton

Discovery
Discovered by	William Lassell
Discovery date	October 10, 1846
Orbital characteristics
Semi-major axis	354,800 km
Eccentricity	0. William Lassell ( June 18 1799 &ndash October 5 1880) was an English Astronomer. Events 680 - Battle of Karbala: Shia Imam Husayn bin Ali, the grandson of the Prophet Muhammad, is decapitated For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 000016[1]
Orbital period	−5. The orbital period is the time taken for a given object to make one complete Orbit about another object 877 d (retrograde)
Inclination	130. 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. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 267° (to the ecliptic) 157. The ecliptic is the apparent path that the Sun traces out in the sky during the year 340° (to Neptune's equator)[2] 130. 063° (to Neptune's orbit)
Satellite of	Neptune
Physical characteristics
Mean radius	1353. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. 4 ± 0. 9 km[3] (0. 2122 Earths)
Surface area	23,018,000 km²[a]
Volume	10,384,000,000 km³[b]
Mass	2. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 14×1022 kg (0. 00359 Earths)[c]
Mean density	2. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 061 g/cm³[3]
Equatorial surface gravity	0. For other uses of the words gram or gramme see Gram (disambiguation. A cubic centimetre or cubic centimeter (symbol cm3 —the abbreviation cc, though widely used is deprecated is a commonly used unit of Volume The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 779 m/s²[d]
Escape velocity	1. In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 455 km/s[e]
Rotation period	synchronous
Sidereal rotation period	5 d, 21 h, 2 min, 53s[4]
Axial tilt	0
Albedo	0. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars In Astronomy, synchronous rotation is a planetological term describing a body orbiting another where the orbiting body takes as long to rotate The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. The albedo of an object is the extent to which it diffusely reflects light from the sun 76[3]
Temperature	38 K[4]
Apparent magnitude	13. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 47[5]
Adjectives	Tritonian
Atmosphere
Surface pressure	0. 0014–9 kPa[4] (1/70,000th the surface pressure on Earth)[6]
Composition	nitrogen; methane traces. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. [7]

Triton (pronounced /ˈtraɪtən/, or as in Greek Τρίτων),^[8] is the largest moon of the planet Neptune, discovered on October 10, 1846 by William Lassell. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Events 680 - Battle of Karbala: Shia Imam Husayn bin Ali, the grandson of the Prophet Muhammad, is decapitated For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display William Lassell ( June 18 1799 &ndash October 5 1880) was an English Astronomer. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. 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. At 2,700 km in diameter, it is the seventh-largest moon in the Solar System. The tables below of Natural satellites in the Solar System are ordered from largest to smallest by average diameter Triton comprises more than 99. 5% of all the mass known to orbit Neptune, including the planet's rings and twelve other known moons. It is also more massive than all the Solar System's 159 known smaller moons combined. ^[f][g]

Because of its retrograde orbit (unique for an object of its size) and similar composition to Pluto, Triton is thought to have been captured from the Kuiper belt. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending ^[9] Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a substantial core of rock and metal. ^[4] The core makes up two-thirds of its total mass. Triton has a mean density of 2. 061 g/cm^3[3] and is composed of approximately 15–35% water ice. ^[4]

Triton is one of the few moons in the Solar System known to be geologically active. Its crust is dotted with geysers believed to erupt nitrogen. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 ^[6] As a consequence, its surface is relatively young, with a complex geological history revealed in intricate and mysterious tectonic terrains. ^[4] Triton has a tenuous nitrogen atmosphere less than 1/70,000^th the pressure of Earth's atmosphere at sea level. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface ^[6]

Discovery and naming

William Lassell, the discoverer of Triton

The moon was discovered by British astronomer William Lassell on October 10, 1846,^[10] just 17 days after Neptune itself was discovered by German astronomers Johann Gottfried Galle and Heinrich Louis d'Arrest. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena William Lassell ( June 18 1799 &ndash October 5 1880) was an English Astronomer. Events 680 - Battle of Karbala: Shia Imam Husayn bin Ali, the grandson of the Prophet Muhammad, is decapitated For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory

A brewer by trade, Lassell began making mirrors for his amateur telescope in 1820. When John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Sir John Frederick William Herschel 1st Baronet KH, FRS ( March 7, 1792 &ndash May 11, 1871)was an Lassell did so and discovered Triton just eight days later. ^[11][10] Lassell also claimed to have discovered rings. However, although Neptune does have rings, they are so faint and dark that it is unlikely he actually observed them. ^[12]

Triton is named after the Greek sea god Triton (Τρίτων), the son of Poseidon (the Greek god comparable to the Roman Neptune). Triton (Τρίτων gen Τρίτωνος is a mythological Greek god, the messenger of the deep In Greek mythology, Poseidon ( Greek:; Latin: Neptūnus) was the god of the Sea and as "Earth-Shaker" Neptune (Neptūnus is the god of water and the sea in Roman mythology, a brother of Jupiter and Pluto. The name was first proposed by Camille Flammarion in his 1880 book Astronomie Populaire,^[13] although it was not officially adopted until many decades later. Nicolas Camille Flammarion ( February 26 1842 &ndash June 3 1925) was a French Astronomer and author ^[14] Until the discovery of the second moon Nereid in 1949, Triton was commonly known as simply "the satellite of Neptune". Nereid (; also as in Greek Νηρηΐδα also known as Neptune II, is a moon of Neptune. Lassell did not name his own discovery, although he suggested names a few years later to his subsequent discovery of an eighth moon of Saturn (Hyperion). TemplateInfobox Planet.--> Hyperion (haɪˈpɪəriən, or as in The third and fourth moons of Uranus (Ariel and Umbriel), which Lassell discovered in 1851, were named by John Herschel. TemplateInfobox Planet.--> Ariel (ˈɛəriəl) is a moon Umbriel (ˈʌmbriəl) is a moon of Uranus discovered on October 24, 1851 by William Lassell. Sir John Frederick William Herschel 1st Baronet KH, FRS ( March 7, 1792 &ndash May 11, 1871)was an ^[15]

Orbit and rotation

Triton is unique among all large moons in the Solar System for its retrograde orbit around its planet (i. 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. e. , it orbits in a direction opposite to the planet's rotation). Most of the outer irregular moons of Jupiter and Saturn also have retrograde orbits, as do some of Uranus' outer moons. In Astronomy, an irregular moon is a Natural satellite following a distant inclined, and often retrograde Orbit. However, these moons are all quite small in comparison; the largest of them (Phoebe)^[h] has only 8% of the diameter (and 0. TemplateInfobox Planet.--> Phoebe (ˈfiːbi, or as in Greek 03% of the mass) of Triton.

Triton's axis of rotation is also unusual, tilted 157 degrees with respect to Neptune's axis, which is in turn inclined 30 degrees from the plane of Neptune's orbit. ^[2] The net result of these two axial tilts is that Triton's rotational axis lies in the plane of Neptune's orbit, and hence during Neptune's year each pole points almost directly toward the Sun, much like Uranus'. As Neptune orbits the Sun, Triton's polar regions take turns facing the sun, probably resulting in radical seasonal changes as one pole then the other moves into the sunlight. The proximity of such a large moon to Neptune has resulted in tidal deceleration, which has altered the moon's orbit and rotation through gravitational interaction. Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i

Triton's revolution around Neptune has become a nearly perfect circle with an eccentricity of almost zero. However, viscoelastic damping from tides alone are not believed to be capable of circularizing Triton's orbit in the time since the origin of the system, and gas drag from a prograde debris disc is likely to have played a substantial role. Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a ^[2] Tidal interactions have also meant that Triton's already close orbit to Neptune is slowly decaying further, and predictions are that, some 3. 6 billion years from now, Triton will pass within Neptune's Roche limit. Determining the Roche limit The Roche limit depends on the rigidity of the satellite ^[16] This will result in either a collision with Neptune's atmosphere or the breakup of Triton, forming a ring system similar to that found around Saturn. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region ^[16]

Capture

The Kuiper belt, from which Triton is believed to have originated

Moons in retrograde orbits cannot have formed out of the same region of the solar nebula as the planets they orbit, but must have been captured from elsewhere. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending The formation and evolution of the Solar System is estimated to have begun Triton is therefore suspected of being captured from the Kuiper belt. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending ^[9] The Kuiper belt is a ring of small icy objects extending outward from just inside the orbit of Neptune to about 55 AU from the Sun. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the Believed to be the point of origin for the majority of short-period comets observed from Earth, it is also home to several large, planet-like bodies including Pluto, which is now recognized as the largest in a population of Kuiper belt objects (the Plutinos) locked in orbital step with Neptune. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — In Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. Triton is only slightly larger than Pluto and nearly identical in composition, which has led to the hypothesis that the two share a common origin.

The proposed capture of Triton may explain several features of the Neptunian system including the extremely eccentric orbit of Neptune's moon Nereid and the scarcity of moons as compared to the other gas giants. Nereid (; also as in Greek Νηρηΐδα also known as Neptune II, is a moon of Neptune. Triton's initially eccentric orbit would have intersected irregular moons and disrupted those of smaller natural moons, dispersing them through gravitational interactions. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape Gravitation is a natural Phenomenon by which objects with Mass attract one another ^[2]

The circularization of Triton's eccentric post-capture orbit would have resulted in heating of the moon by tidal forces. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced These would have kept Triton liquid for a billion years, which is supported by evidence of differentiation in the moon's interior. ^[6] Its similarity in size and composition to Pluto provides further confirmation of Triton's possible origin as a Pluto-like planetary body in the Kuiper belt. ^[17]

There are two ways which Triton's capture may have occurred. In order to be gravitationally captured by a planet, a moon must be slowed down by losing energy. An early theory of how Triton may have been slowed was by collision with another object, either one that happened to be passing by Neptune (which is unlikely), or a moon or proto-moon in orbit around Neptune (which is more likely). ^[4] Another hypothesis suggests that, before its capture, Triton may have had a massive companion similar to Pluto's moon Charon with which it formed a binary. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double When the binary encountered Neptune, Triton's companion was expelled, providing the required mechanism to capture Triton in an orbit around the planet. This hypothesis is supported by several lines of evidence, including binaries being very common among the large Kuiper belt objects. ^[18] The event was brief but gentle, saving Triton from collisional disruption; and events like this may have been common during the formation of Neptune, or later when it migrated outward. Planetary migration occurs when a Planet or other stellar satellite interacts with a disk of gas or Planetesimals resulting in the alteration of the satellite's orbital ^[9]

Physical characteristics

Triton has a similar size, density (2. 061 g/cm³), temperature and chemical composition to that of Pluto. ^[19] As with Pluto, 55% of Triton's surface is covered with frozen nitrogen, with water ice comprising 15–35% and dry ice (frozen carbon dioxide) forming the remaining 10–20%. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Dry ice is solid Carbon dioxide. It is commonly used as a versatile cooling agent Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Traces include 0. 1% methane and 0. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 05% carbon monoxide ice. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. ^[4] There could be ammonia on the surface that resulted from possible ammonia dihydrate in the lithosphere. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. ^[20] This density means Triton is probably about 30–45% water ice, with the remainder being rocky material. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia ^[4] Triton's surface area is 23 million km², which is 4. 5% of Earth, or 15. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 5% of Earth's land area. Triton is very bright, reflecting 60–95% of the sunlight that reaches it. By comparison, Earth's moon reflects only 11%. ^[21] Triton's reddish colour is believed to be the result of methane ice which reduces to carbon under bombardment from ultraviolet radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays ^[4]

Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like Earth, into a solid core, a mantle and a crust. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided In Geology, a crust is the outermost solid shell of a planet or moon Water, the most abundant volatile in the Solar System, comprises the moon's mantle, which lies over a core of rock and metal. Water is a common Chemical substance that is essential for the survival of all known forms of Life. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's There is enough rock in Triton's interior for solid-state convection to be occurring within its mantle, powered by radioactive decay. Convection in the most general terms refers to the movement of molecules within Fluids (i Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The heat may even be sufficient to maintain a "subterranean ocean" similar to that which is hypothesized to exist underneath the surface of Europa. TemplateInfobox Planet.--> Europa (jʊˈroʊpə; or as ^[4] The possible presence of a layer of liquid water suggests the possibility, if unlikely, of life. ^[22]

Atmosphere

Main article: Atmosphere of Triton

A cloud over the limb of Triton

Triton has a tenuous nitrogen atmosphere with small amounts of methane near the surface. The Atmosphere of Triton extends 800 kilometers above Triton's surface ^[7][23] Like Pluto's atmosphere, the atmosphere of Triton is believed to have resulted from evaporation of nitrogen from the moon's surface. ^[17] The surface temperature is at least 35. 6 K (−237. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic 6 °C) because Triton's nitrogen ice is in the warmer, hexagonal crystalline state, and the phase transition between hexagonal and cubic nitrogen ice occurs at that temperature. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 ^[24] An upper limit with kelvins in the low 40s can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. ^[25] This temperature range is colder than Pluto's average equilibrium temperature of 44 K (−229 °C). Triton's surface atmospheric pressure is only about 1. 4–1. 9 pascal (0. 014–0. 019 millibar). The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. ^[4]

Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and Streaks on Triton's surface left by geyser plumes suggest that the troposphere is driven by seasonal winds capable of moving material of over a micrometre in size. ^[26] Unlike other atmospheres, Triton's has no stratosphere, and instead consists of a thermosphere from 8 to 950 km above the surface, and an exosphere above that. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. ^[4] The temperature of Triton's upper atmosphere, at 95 ± 5 kelvins, is higher than the temperature at the surface due to heat deposited from space. ^[7] A haze permeates most of Triton's troposphere, believed to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. A nitrile is any Organic compound which has a - C ≡ N Functional group. Triton's atmosphere also possesses clouds of condensed nitrogen that lie between 1 and 3 km from the surface. ^[4]

In the 1990s, observations from Earth were made of Triton's limb as the moon passed in front of stars. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Limb darkening refers to the diminishing of intensity in the image of a star as one moves from the center of the image to the edge or " Limb " of the image In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. These observations indicated the presence of a denser atmosphere than was thought from Voyager 2 data. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[27] Other observations have shown an increase in temperature by 5% from 1989 to 1998. ^[28] These observations indicate Triton is approaching an unusually warm summer season that only happens once every few hundred years. Theories for this warming include a change of frost patterns on Triton's surface and a change in ice albedo, which would allow more heat to be absorbed. ^[29] Another theory argues the changes in temperature are a result of deposition of dark, red material from geological processes on the moon. Because Triton's Bond albedo is among the highest within the Solar System, it is sensitive to small variations in spectral albedo. The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The albedo of an object is the extent to which it diffusely reflects light from the sun ^[30]

Surface features

All detailed knowledge of the surface of Triton was acquired in a single encounter by the Voyager 2 spacecraft in 1989. The 40% of Triton's surface imaged by Voyager revealed rocky outcrops, canyons and icy melt, mainly frozen methane. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Triton is relatively flat; its observed topography never varies beyond a kilometer. ^[4] There are relatively few impact craters on Triton. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body Recent analysis of crater density and distribution has suggested that in geological terms, Triton's surface is extremely young, with regions varying from 50 million years old to just 6 million years old. ^[31]

Cryovolcanism

Main article: Cryovolcano

Bluish streaks across Triton's surface believed to have been left by eruptions from nitrogen geysers

Triton is geologically active; its surface is young and has relatively few impact craters. A cryovolcano is literally an Icy Volcano. Cryovolcanoes form on Icy moons and possibly on other low- Temperature Astronomical objects Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 When the Voyager 2 probe studied Triton, it observed numerous icy volcanoes or geysers erupting liquid nitrogen, dust, or methane compounds from beneath the surface in plumes up to 8 km high. A cryovolcano is literally an Icy Volcano. Cryovolcanoes form on Icy moons and possibly on other low- Temperature Astronomical objects A geyser is a Hot spring characterized by intermittent discharge of water ejected turbulently and accomplished by a vapour phase Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of ^[19] Although Triton is made of various ices, its subsurface processes are similar to those that produce volcanoes and rift valleys on Earth, but with water and ammonia lavas as opposed to liquid rock. Plate tectonics and hotspots Divergent plate boundaries At the A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic Rift or fault. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor ^[4]

The volcanic activity is thought to be driven by seasonal heating from the Sun, unlike the tidal heating responsible for the volcanoes of Io. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek ^[26] Solar heat is trapped under surface nitrogen ice, which creates a form of "solid greenhouse effect", slowly heating the subsurface until nitrogen beneath evaporates and erupts through the crust. The Greenhouse effect refers to the change in the Thermal equilibrium temperature of a planet or moon by the presence of an Atmosphere containing gas that absorbs ^[4] Between 1977 and the Voyager flyby in 1989, Triton shifted from a reddish colour, similar to Pluto, to a far paler hue, suggesting that cryovolcanism in the intervening decade had covered older reddish material with lighter nitrogen frosts. A cryovolcano is literally an Icy Volcano. Cryovolcanoes form on Icy moons and possibly on other low- Temperature Astronomical objects ^[4]

Triton's entire surface is cut by complex valleys and ridges, probably the result of tectonics and icy volcanism. Plate tectonics and hotspots Divergent plate boundaries At the The vast majority of surface features on Triton are endogenic—the result of internal geological processes rather than external processes such as impacts. Exogenic redirects here for the record label see Exogenic Records. Most are volcanic and extrusive in nature, rather than tectonic. ^[4] Hili and Mahilani are two candidate cryovolcanoes that have been observed on Triton. A cryovolcano is literally an Icy Volcano. Cryovolcanoes form on Icy moons and possibly on other low- Temperature Astronomical objects (They are named after a Zulu water sprite and a Tongan sea spirit, respectively. Zulu mythology contains numerous deities, commonly associated with animals or general classes of natural phenomena In Zulu mythology, Tikoloshe, Tokoloshe or Hili (from the Xhosa word utyreeci ukujamaal) is a Dwarf -like water sprite The Kingdom of Tonga is an Archipelago in the south Pacific Ocean comprising 169 islands 36 of them inhabited stretching over a distance of about 800 kilometres (500 miles )^[32] Triton thus joins the Earth, Io, and Enceladus as one of the few worlds of the Solar System with current known volcanic activity. TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek TemplateInfobox Planet.--> This article is about the moon of ^[33] (Venus, Mars, Titan, and Dione may also be volcanically active. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as TemplateInfobox Planet.--> Dione (daɪˈoʊni, or as in Greek ) The eruption of volatiles from Triton's equator and its deposition at the poles may redistribute enough mass over the course of 10,000 years to cause polar wander. ' Polar wander' is the phenomenon in which the North and South Poles of the Earth move with respect to the continents ^[34]

Polar cap, plains and ridges

Triton's bright red south polar cap

The southern polar region of Triton is covered by a highly reflective cap of frozen nitrogen and methane sprinkled by impact craters and openings of geysers. Little is known about the north pole because it was on the night side during the Voyager 2 encounter. However, it is thought that Triton must also have a north polar cap. ^[24]

The high plains found on Triton's eastern hemisphere cover over and blot out older features, and are therefore almost certainly the result of icy lava washing over the previous landscape. The plains are dotted with pits, such as Leviathan Patera, which are probably the vents from which this lava emerged. The composition of the lava is unknown, although a mixture of ammonia and water is suspected. ^[4]

Four roughly circular "walled plains" have been identified on Triton. They are the flattest regions so far discovered, with a variance in altitude of less than 200 m. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International They are believed to have formed from eruption of icy lava. ^[4] The plains near Triton's eastern limb are dotted with black points, the maculae. Macula (pl maculae) is the Latin word for 'spot' It is used in Planetary geology to refer to unusually dark areas on the surface of a Planet Each of the maculae comprises a dark central patch surrounded by a white halo of material. They all have similar diameters of between 20 and 30 km. Some speculate the maculae are outliers of the southern polar cap, which is in retreat in summer. ^[4]

There are extensive ridges and valleys in complex patterns across Triton's surface, probably the result of freeze–thaw cycles. ^[35] Many also appear to be tectonic in nature and may result from extension or strike-slip faulting. In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement ^[36] Some bear a strong resemblance to ridges on Europa, and may have a similar origin. ^[4] In the equatorial region, long faults with parallel mountain ranges of ice expelled from the interior cross complex terrain with valleys. These ridges, or sulci, such as Yasu Sulci, Ho Sulci, and Lo Sulci,^[37] are believed to be of intermediate age in Triton's geological history, and in many cases to have formed concurrently. They tend to be clustered in groups or "packets". ^[36]

Cantaloupe terrain

The cantaloupe-skin terrain as seen from 130,000 km by Voyager 2

Triton's western hemisphere consists of a strange series of fissures and depressions known as "cantaloupe terrain" because of its resemblance to the skin of a cantaloupe melon. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Cantaloupe (also cantaloup) refers to two varieties of Muskmelon ( Cucumis melo), which is a Species in the family Cucurbitaceae (a Although it has few craters, it is believed that this is the oldest terrain on Triton. ^[38] It probably covers much of the western half of the moon. ^[4]

The cantaloupe terrain, which is mostly dirty frozen water, is known to exist only on Triton. It contains depressions 30–40 km in diameter. ^[38] The depressions (cavi) are probably not impact craters by meteorites because they are all of similar size and have smooth curves. The leading hypothesis as to their formation is diapirism, the rising of "lumps" of less dense material through a stratum of denser material. A diapir (ˈdaɪəpɪər) ( French, from Greek diapeirein, to pierce through is an Intrusion caused by Buoyancy and Pressure ^[4] Other hypotheses of the region's formation include that it formed by collapses, or by flooding caused by cryovolcanism. A cryovolcano is literally an Icy Volcano. Cryovolcanoes form on Icy moons and possibly on other low- Temperature Astronomical objects ^[38]

Impact craters

The few craters that exist on Triton reveal intense geologic activity

Due to constant erasure and modification by ongoing geological activity, impact craters on Triton's surface are relatively rare. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body A census of Triton's craters imaged by Voyager 2 found only 179 that were incontestably of impact origin, compared with 835 observed for Uranus' moon Miranda, which has only three percent of Triton's surface area. TemplateInfobox Planet.--> Miranda (mɨˈrændə) is the smallest Surface area is the measure of how much exposed Area an object has ^[39] The largest crater observed on Triton believed to have been created by an impact is a 27 km-diameter feature called Mazomba. ^[39][40] Although larger craters have been observed, they are generally believed to be volcanic in nature. ^[39]

The few impact craters on Triton are almost all concentrated in the leading hemisphere–that facing the direction of the orbital motion—with the majority concentrated around the equator between 30° and 70° longitude,^[39] resulting from material swept up from orbit around Neptune. ^[31] Because it orbits with one side permanently facing the planet, astronomers expect that Triton should have fewer impacts on its trailing hemisphere, as impacts on the leading hemisphere would be more frequent and more violent. ^[39] However, as Voyager only imaged 40% of Triton's surface, this remains uncertain.

Observation

Neptune and Triton three days after the flyby of Voyager 2

The orbital properties of Triton had been defined with high accuracy in the 19th century, but little was known about the satellite itself until Voyager 2 arrived at the end of the 20th century. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. The first detailed observations of Triton were not made until 1930. It was found to have a retrograde orbit, at a very high angle of inclination to the plane of Neptune's orbit. ^[4]

Before the arrival of Voyager 2, astronomers suspected that Triton might have liquid nitrogen seas and a nitrogen/methane atmosphere with a density as much as 30% that of the Earth. Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of Like the famous overestimates of the atmospheric density of Mars, this was completely false. As with Mars, a denser early atmosphere is postulated for the body's early history. ^[41]

The first attempt to measure the diameter of Triton was made by Gerard Kuiper in 1954. Gerard Peter Kuiper ( born Gerrit Pieter Kuiper ( ( December 7 1905, Harenkarspel ( Tuitjenhorn) Netherlands &ndash He obtained a value of 3,800 km. Subsequent measurement attempts arrived at values ranging from 2,500 to 6,000 km, or slightly smaller than our Moon, to nearly half the diameter of Earth. ^[42] Data from the approach of Voyager 2 to Neptune on August 25, 1989 led to a more accurate estimate of Triton's diameter (2,706 km). Events 1248 - The Dutch city of Ommen receives city rights and fortification rights from Otto III the Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) ^[43]

In the 1990s, various observations from Earth were made of the limb of Triton using the occultation of nearby stars, which indicated the presence of an atmosphere and an exotic surface. The observations suggest that the atmosphere is denser than the Voyager 2 measurements had indicated. ^[27]

See also

• List of geological features on Triton
• Neptune's moons in fiction

Notes

References

External links

• Triton Profile by NASA's Solar System Exploration