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, known as (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).
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
Macula is the Latin word for 'spot'. It is used in planetary nomenclature to refer to unusually dark areas on the surface of a planet or moon. They are seen on the icy surfaces of Pluto, Jupiter's moon Europa, Saturn's moon Titan, Neptune's moon Triton, and Pluto's moon Charon. The term was adopted for planetary nomenclature when high resolution pictures of Europa revealed unusual new surface features.
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.
A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System. The prototypical dwarf planet is Pluto, which for decades was regarded as a planet before the "dwarf" concept was adopted in 2006.
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.
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.
Sputnik Planitia is a large, partially glaciated basin on Pluto. About 1,400 by 1,200 km in size, Sputnik Planitia is partially submerged in large, bright glaciers of nitrogen ice. Named after Earth's first artificial satellite, Sputnik 1, it constitutes the western lobe of the heart-shaped Tombaugh Regio. Sputnik Planitia lies mostly in the northern hemisphere, but extends across the equator. Much of it has a surface of irregular polygons separated by troughs, interpreted as convection cells in the relatively soft nitrogen ice. The polygons average about 33 km (21 mi) across. In some cases troughs are populated by blocky mountains or hills, or contain darker material. There appear to be windstreaks on the surface with evidence of sublimation. The dark streaks are a few kilometers long and all aligned in the same direction. The planitia also contains pits apparently formed by sublimation. No craters were detectable by New Horizons, implying a surface less than 10 million years old. Modeling sublimation pit formation yields a surface age estimate of 180000+90000
−40000 years. Near the northwest margin is a field of transverse dunes, spaced about 0.4 to 1 km apart, that are thought to be composed of 200-300 μm diameter particles of methane ice derived from the nearby Al-Idrisi Montes.
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.
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 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. Ruach Planitia, along with the other walled plains on Triton, is one of the youngest and flattest features on Triton.
