Triton is the largest natural satellite of the planet Neptune. It is the only moon of Neptune massive enough to be rounded under its own gravity and hosts a thin but well-structured atmosphere. Triton orbits Neptune in a retrograde orbit—an orbit in the direction opposite to its planet's rotation—the only large moon in the Solar System to do so. Triton is thought to have once been a dwarf planet, captured from the Kuiper belt into Neptune orbit.
Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume, by a small margin, but is less massive than Eris. Like other Kuiper belt objects, Pluto is made primarily of ice and rock and is much smaller than the inner planets. Pluto has roughly one-sixth the mass of Earth's moon, and one-third its volume.
Charon, or (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake, and Gonggong. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).
The planet Neptune has 16 known moons, which are named for minor water deities and a water creature in Greek mythology. By far the largest of them is Triton, discovered by William Lassell on 10 October 1846, 17 days after the discovery of Neptune itself. Over a century passed before the discovery of the second natural satellite, Nereid, in 1949, and another 40 years passed before Proteus, Neptune's second-largest moon, was discovered in 1989.
A cryovolcano is a type of volcano that erupts gases and volatile material such as liquid water, ammonia, and hydrocarbons. The erupted material is collectively referred to as cryolava; it originates from a reservoir of subsurface cryomagma. Cryovolcanic eruptions can take many forms, such as fissure and curtain eruptions, effusive cryolava flows, and large-scale resurfacing, and can vary greatly in output volumes. Immediately after an eruption, cryolava quickly freezes, constructing geological features and altering the surface.
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena, plural catenae, as specified by the International Astronomical Union's rules on planetary nomenclature.
The geology of Pluto consists of the characteristics of the surface, crust, and interior of Pluto. Because of Pluto's distance from Earth, in-depth study from Earth is difficult. Many details about Pluto remained unknown until 14 July 2015, when New Horizons flew through the Pluto system and began transmitting data back to Earth. When it did, Pluto was found to have remarkable geologic diversity, with New Horizons team member Jeff Moore saying that it "is every bit as complex as that of Mars". The final New Horizons Pluto data transmission was received on 25 October 2016. In June 2020, astronomers reported evidence that Pluto may have had a subsurface ocean, and consequently may have been habitable, when it was first formed.
The atmosphere of Triton is the layer of gases surrounding Triton. Like the atmospheres of Titan and Pluto, Triton's atmosphere is composed primarily of nitrogen, with smaller amounts of methane and carbon monoxide. It hosts a layer of organic haze extending up to 30 kilometers above its surface and a deck of thin bright clouds at about 4 kilometers in altitude. Due to Triton's low gravity, its atmosphere is loosely bound, extending over 800 kilometers from its surface.
Planetary oceanography, also called astro-oceanography or exo-oceanography, is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry, and planetary geology, it only began after the discovery of underground oceans in Saturn's moon Titan and Jupiter's moon Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons. There are many theories about oceans or even ocean worlds of celestial bodies in the Solar System, from oceans made of diamond in Neptune to a gigantic ocean of liquid hydrogen that may exist underneath Jupiter's surface.
Mordor Macula is the informal name for a large dark area about 475 km in diameter near the north pole of Charon, Pluto's largest moon. It is named after the black land called Mordor in J.R.R. Tolkien's The Lord of the Rings.
The geology of Charon encompasses the characteristics of the surface, crust, and interior of Pluto's moon Charon. Like the geology of Pluto, almost nothing was known of Charon's geology until the New Horizons of the Pluto system on 14 July 2015. Charon's diameter is 1,208 km (751 mi)—just over half that of Pluto. Charon is sufficiently massive to have collapsed into a spheroid under its own gravity.
Vulcan Planitia, or Vulcan Planum, is the unofficial name given to a large plain on the southern hemisphere of Pluto's moon Charon. It discovered by New Horizons during its flyby of Pluto in July 2015. It is named after the fictional planet Vulcan in the science-fiction series Star Trek. The name is not approved by International Astronomical Union (IAU) as of 2024.
PateraPAT-ər-ə is an irregular crater, or a complex crater with scalloped edges on a celestial body. Paterae can have any origin, although the majority of them were created by volcanism. The term comes from Latin, where it refers to a shallow bowl used in antique cultures.
Set Catena is a pit chain (catena) and likely tectonic fault located on Triton, the largest natural satellite of Neptune. It, along with Kraken Catena, is located near Leviathan Patera, a major cryovolcanic feature; as such, Set Catena may have played a role in rift-induced cryovolcanic activity in Leviathan Patera. Set Catena extends radially northwards from Leviathan Patera, terminating at another irregularly-shaped walled depression. Set Catena consists of semi-regularly spaced pits roughly 20 km separated from each other, with each pit being on average 10 km wide and up to 500 m deep. The pits may have formed from collapse or from explosive cryovolcanic eruptions, and may have been subsequently expanded by mass wasting processes. Set Catena may be a northeastern extension of Raz Fossae, a similar fault system southwest of Leviathan Patera.
Leviathan Patera is a major cryovolcanic caldera on Neptune's largest moon Triton. Discovered by the Voyager 2 spacecraft in 1989, Leviathan Patera is located in Monad Regio and within Cipango Planum's western regions. Leviathan Patera is approximately 80 kilometers in diameter and may be the center of one of the largest cryovolcanic or volcanic edifices in the Solar System.
The geology of Triton encompasses the physical characteristics of the surface, internal structure, and geological history of Neptune's largest moon Triton. With a mean density of 2.061 g/cm3, Triton is roughly 15-35% water ice by mass; Triton is a differentiated body, with an icy solid crust atop a probable subsurface ocean and a rocky core. As a result, Triton's surface geology is largely driven by the dynamics of water ice and other volatiles such as nitrogen and methane. Triton's geology is vigorous, and has been and continues to be influenced by its unusual history of capture, high internal heat, and its thin but significant atmosphere.
Tuonela Planitia is an elongated plain and probable cryolava lake on Neptune's moon Triton. Located in Triton's northern hemisphere within Monad Regio, it overlies part of Triton's unusual cantaloupe terrain. As with neighboring Ruach Planitia and the other walled plains on Triton, Tuonela Planitia is among the youngest features on Triton's surface.
Ruach Planitia is a roughly circular flat plain and probable cryolava lake on Neptune's moon Triton. It is located in Triton's northern hemisphere within Monad Regio and directly borders the cryovolcanic plains of Cipango Planum to the east and Tuonela Planitia to the west. Ruach Planitia, along with the other three walled plains of Triton, is one of the youngest and flattest features observed on the moon.
Slidr Sulci is a major tectonic fault on Neptune's largest moon Triton. It crosses a wide variety of terrains on Triton, most prominently the cantaloupe terrain, an unusually-textured region resembling the skin of a North American cantaloupe. The fault is named after the River Sliðr of Norse mythology, whose waters in Hel are filled with swords. The name Slidr Sulci was officially approved by the International Astronomical Union (IAU) in 1991. As with all of Triton's surface features, Slidr Sulci was first observed by the Voyager 2 spacecraft on its flyby of Neptune and Triton in 1989.
