"inclined relative to Neptune's equator, which suggests that it did not form in orbit around Neptune but was instead gravitationally captured by it. The next-largest irregular satellite in the Solar System, Saturn's moon Phoebe, has only 0.03% of Triton's mass. The capture of Triton, probably occurring some time after Neptune formed a satellite system, was a catastrophic event for Neptune's original satellites, disrupting their orbits so that they collided to form a rubble disc. Triton is massive enough to have achieved hydrostatic equilibrium and to retain a thin atmosphere capable of forming clouds and hazes. Inward of Triton are seven"
"Proteus (moon) Proteus ( ; Greek: ""Πρωτεύς""), also known as Neptune VIII, is the second-largest Neptunian moon, and Neptune's largest inner satellite. Discovered by ""Voyager 2"" spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology. Proteus orbits Neptune in a nearly equatorial orbit at the distance of about 4.75 equatorial radii of the planet. Despite being a predominantly icy body more than 400 km in diameter, Proteus's shape deviates significantly from an ellipsoid. It is shaped more like an irregular polyhedron with several slightly concave facets and relief as high as 20 km. Its"
"Nereid (moon) Nereid is the third-largest moon of Neptune. It has a highly eccentric orbit. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949. Nereid was discovered on 1 May 1949 by Gerard P. Kuiper on photographic plates taken with the 82-inch telescope at the McDonald Observatory. He proposed the name in the report of his discovery. It is named after the Nereids, sea-nymphs of Greek mythology and attendants of the god Neptune. It was the second and last moon of Neptune to be discovered before the arrival of Voyager 2 (not counting a"
"Triton Hopper Triton Hopper is a proposed NASA lander to Triton, the largest moon of Neptune. The idea is to harvest the abundant nitrogen ice on the surface of Triton and use it as propellant for multiple short flights and explore a variety of locations. The concept transitioned in March 2018 to Phase II to refine their designs and explore aspects of implementing the new technology. Triton is the largest moon of Neptune. In 1989, ""Voyager 2"" flew past the moon at a distance of 40,000 km, and discovered several cryovolcanoes on its surface. Triton is geologically active; its surface"
"Neptune Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of . It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the"
"Ganymede (moon) Ganymede (Jupiter III) is the largest and most massive moon of Jupiter and in the Solar System. The ninth largest object in the Solar System, it is the largest without a substantial atmosphere. It has a diameter of and is 8% larger than the planet Mercury, although only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. It is the third of the Galilean moons, the first group of objects discovered orbiting another"
"Neso (moon) Neso ( ; Greek: ""Νησώ""), also known as Neptune XIII, is the outermost known natural satellite of Neptune. It is an irregular moon discovered by Matthew J. Holman, Brett J. Gladman, ""et al."" on August 14, 2002, though it went unnoticed until 2003. Neso orbits Neptune at a distance of more than 48 Gm (million km), making it (as of 2015) the most distant known moon of any planet. At apocenter, the satellite is more than 72 Gm from Neptune. This distance is great enough to exceed Mercury's aphelion, which is approximately 70 Gm from the Sun. Neso"
"the most eccentric of the large moons of the Solar System. The four Galilean moons have eccentricity < 0.01. Neptune's largest moon Triton has an eccentricity of (), 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. However, smaller moons, particularly irregular moons, can have significant eccentricity, such as Neptune's third largest moon Nereid (0.75). Comets have very different values of eccentricity. Periodic comets have eccentricities mostly between 0.2 and 0.7, but some of them have highly eccentric elliptical orbits with eccentricities just below"
"to the planet. Proteus is the second-largest moon of Neptune. It is about 420 kilometres in diameter, larger than Nereid, the second to be discovered. It was not discovered by Earth-based telescopes because it is so close to Neptune that it is lost in the glare of reflected sunlight. The surface of Proteus is dark—its geometrical albedo is about 10%. The color of its surface is neutral as the reflectivity does not change appreciably with the wavelength from violet to green. In the near-infrared around 2 μm Proteus's surface becomes less reflective, pointing to a possible presence of complex organic"
"winds of any planet in the Solar System, measured as high as 2,100 km/h. ""Voyager 2"" also examined Neptune's ring and moon system. It discovered 900 complete rings and additional partial ring ""arcs"" around Neptune. In addition to examining Neptune's three previously known moons, ""Voyager 2"" also discovered five previously unknown moons, one of which, Proteus, proved to be the last largest moon in the system. Data from ""Voyager 2"" supported the view that Neptune's largest moon, Triton, is a captured Kuiper belt object. The dwarf planet Pluto presents significant challenges for spacecraft because of its great distance from Earth"
"despite the fact that Triton is more than 4 times as intrinsically bright as our moon and orbits much closer to Neptune. Triton, Neptune's largest moon, has an atmosphere, but it is so thin that its sky is still black, possibly with some pale haze at the horizon. Because Triton orbits with synchronous rotation, Neptune always appears in the same position in its sky. Triton's rotation axis is inclined 130° to Neptune's orbital plane and thus points within 40° of the Sun twice per Neptunian year, much like Uranus's. As Neptune orbits the Sun, Triton's polar regions take turns facing"
"Neith (crater) Neith crater is a crater on Jupiter's moon Ganymede, the largest moon in the solar system. Impact features like Neith have been called ""penepalimpsests"" by some investigators or ""dome craters"" by others and are considered to be transitional between craters and palimpsests. Palimpsests are bright, nearly circular patches that are believed to be remnant impact features. They occur also on Callisto, Ganymede's neighbor farther distant from Jupiter. The most striking feature in Neith is a large, circular dome about 45 km in diameter. The dome is surrounded by a wreath of rugged terrain. The wreath does not represent"
"Titan (moon) Titan is the largest moon of Saturn. It is the only moon known to have a dense atmosphere, and the only object in space, other than Earth, where clear evidence of stable bodies of surface liquid have been found. Titan is the sixth gravitationally rounded moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the smallest planet, Mercury, but only 40% as massive. Discovered in 1655 by the Dutch astronomer"
"regular moons are Naiad, Thalassa, Despina, Galatea, Larissa, Neptune XIV, and Proteus. All but the outer two are within Neptune-synchronous orbit (Neptune's rotational period is 0.6713 day) and thus are being tidally decelerated. Naiad, the closest regular moon, is also the second smallest among the inner moons (following the discovery of Neptune XIV), whereas Proteus is the largest regular moon and the second largest moon of Neptune. The inner moons are closely associated with Neptune's rings. The two innermost satellites, Naiad and Thalassa, orbit between the Galle and LeVerrier rings. Despina may be a shepherd moon of the LeVerrier ring,"
"Ganymede in greater detail than previously. However, the mission was canceled in 2005 because of budget cuts. Another old proposal was called The Grandeur of Ganymede. Ganymede (moon) Ganymede (Jupiter III) is the largest and most massive moon of Jupiter and in the Solar System. The ninth largest object in the Solar System, it is the largest without a substantial atmosphere. It has a diameter of and is 8% larger than the planet Mercury, although only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and"
"the expansion continued, but some of the angular moment was transferred to Europa as the resonance caused its orbit to expand as well; the process continued until Europa encountered the 2:1 resonance with Ganymede. Eventually the drift rates of conjunctions between all three moons were synchronized and locked in the Laplace resonance. Ganymede is the largest and most massive moon in the Solar System. Its diameter of 5,268 km is 0.41 times that of Earth, 0.77 times that of Mars, 1.02 times that of Saturn's Titan (the second-largest moon), 1.08 times Mercury's, 1.09 times Callisto's, 1.45 times Io's and 1.51"
"Titania (moon) Titania is the largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of . Discovered by William Herschel in 1787, Titania is named after the queen of the fairies in Shakespeare's ""A Midsummer Night's Dream"". Its orbit lies inside Uranus's magnetosphere. Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the core–mantle boundary. The surface of Titania, which is relatively dark and slightly red in color, appears"
"Saturn Rhea is the second-largest moon of Saturn. Titan is the largest moon of Saturn. Its substantial atmosphere makes it the most Earth-like moon in the Solar System and hence a popular science fiction setting. Hyperion is the largest irregularly-shaped moon of Saturn, orbiting between Titan and Iapetus. Iapetus is a large moon orbiting further from Saturn than any of its other large satellites. Half of its surface is very bright while the other half is extremely dark. Investigations since 2004 have also noted its irregular shape, immense impact basins, and a high mountainous ridge on the equator. Phoebe is"
"shorter period (5.8 days) compounded by its retrograde orbit. The smaller moon Proteus would show a disk about half the size of the full Moon. Surprisingly, Neptune's small inner moons all cover, at some point in their orbits, more than 10′ in Neptune's sky. At some points, Despina's angular diameter rivals that of Ariel from Uranus and Ganymede from Jupiter. Here are the angular diameters for Neptune's moons (for comparison, Earth's moon measures on average 31′ for terrestrial observers): Naiad, 7–13′; Thalassa, 8–14′; Despina, 14–22′; Galatea, 13–18′; Larissa, 10–14′; Proteus, 12–16′; Triton, 26–28′. An alignment of the inner moons would"
"Callisto (moon) </math>.</ref> Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about . It is not in an orbital resonance like the three other"
"thirteen. Follow-up surveys by two teams in 2002 and 2003 respectively re-observed all five of these moons, which are Halimede, Sao, Psamathe, Laomedeia, and Neso. A sixth candidate moon was also found in the 2002 survey and was lost thereafter: it may have been a centaur instead of a satellite, although its small amount of motion relative to Neptune over a month suggests that it was indeed a satellite. It was estimated to have a diameter of 33 km and to have been about 25.1 million km (0.168 AU) from Neptune when it was found. Mark Showalter discovered Neptune XIV"
"though the presence of ammonia on Titan would cause chemical reactions to proceed more slowly. Titan (moon) Titan is the largest moon of Saturn. It is the only moon known to have a dense atmosphere, and the only object in space, other than Earth, where clear evidence of stable bodies of surface liquid have been found. Titan is the sixth gravitationally rounded moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the"
"Neptune XIV Neptune XIV, originally known as S/2004 N 1, is a small moon of Neptune, about in diameter, which orbits the planet in just under one Earth day. Its discovery on 1 July 2013 increased the number of Neptune's known satellites to fourteen. The moon is so dim that it was not observed when ""Voyager 2"" flew by in 1989. Mark Showalter of the SETI Institute found it by analyzing archived Neptune photographs the Hubble Space Telescope captured between 2004 and 2009. The moon was formally numbered Neptune XIV (14) on 25 September 2018 in Minor Planet Circular 111804."
"by Jupiter. Neptune's equatorial radius of 24,764 km is nearly four times that of Earth. Neptune, like Uranus, is an ice giant, a subclass of giant planet, because they are smaller and have higher concentrations of volatiles than Jupiter and Saturn. In the search for extrasolar planets, Neptune has been used as a metonym: discovered bodies of similar mass are often referred to as ""Neptunes"", just as scientists refer to various extrasolar bodies as ""Jupiters"". Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the"
"Puck (moon) Puck ( ) is an inner moon of Uranus. It was discovered in December 1985 by the ""Voyager 2"" spacecraft. The name ""Puck"" follows the convention of naming Uranus's moons after characters from Shakespeare. The orbit of Puck lies between the rings of Uranus and the first of Uranus's large moons, Miranda. Puck is approximately spherical in shape and has diameter of about 162 km. It has a dark, heavily cratered surface, which shows spectral signs of water ice. Puck—the largest inner moon of Uranus—was discovered from the images taken by ""Voyager 2"" on 30 December 1985. It"
"son of Poseidon and Thoosa. Neptune XIV Neptune XIV, originally known as S/2004 N 1, is a small moon of Neptune, about in diameter, which orbits the planet in just under one Earth day. Its discovery on 1 July 2013 increased the number of Neptune's known satellites to fourteen. The moon is so dim that it was not observed when ""Voyager 2"" flew by in 1989. Mark Showalter of the SETI Institute found it by analyzing archived Neptune photographs the Hubble Space Telescope captured between 2004 and 2009. The moon was formally numbered Neptune XIV (14) on 25 September 2018"
"Iapetus (moon) Iapetus (; ), or occasionally Japetus , is the third-largest natural satellite of Saturn, eleventh-largest in the Solar System, and the largest body in the Solar System known not to be in hydrostatic equilibrium. Iapetus is best known for its dramatic ""two-tone"" coloration. Discoveries by the ""Cassini"" mission in 2007 revealed several other unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon. Iapetus was discovered by Giovanni Domenico Cassini, an Italian astronomer, in October 1671. He had discovered it on the western side of Saturn and tried viewing it on the"
"an extended mission. Another mission concept proposed was the Uranus orbiter and probe concept, evaluated around 2010. Uranus was also examined as part of one trajectory for a precursor interstellar probe concept, Innovative Interstellar Explorer. A Uranus orbiter was listed as the third priority for a NASA Flagship mission by the NASA Planetary Science Decadal Survey, and conceptual designs for such a mission are currently being analyzed. Titania (moon) Titania is the largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of . Discovered by William Herschel in 1787, Titania is"
"both irregular satellites could have a common origin in the break-up of a larger moon. Neso is named after one of the Nereids. Before the announcement of its name on February 3, 2007 (IAUC 8802), Neso was known by its provisional designation, S/2002 N 4. Notes Citations Neso (moon) Neso ( ; Greek: ""Νησώ""), also known as Neptune XIII, is the outermost known natural satellite of Neptune. It is an irregular moon discovered by Matthew J. Holman, Brett J. Gladman, ""et al."" on August 14, 2002, though it went unnoticed until 2003. Neso orbits Neptune at a distance of more"
"that are more massive than Eris are the Moon, the four Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto), one moon of Saturn (Titan), and one moon of Neptune (Triton). The others are six moons of Saturn (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus), five moons of Uranus (Miranda, Ariel, Umbriel, Titania, and Oberon), and one moon of Pluto (Charon). There are additional possibilities among TNOs, including Dysnomia orbiting Eris. Alan Stern calls these moons ""satellite planets"", one of three categories of planet together with dwarf planets and classical planets. The term ""planemo"" (""planetary-mass object"") covers all three. In"
"Galilean moons The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in January 1610, and recognized by him as satellites of Jupiter in March 1610. They were the first objects found to orbit another planet. Their names derive from the lovers of Zeus. They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with a radius larger than any of the dwarf planets. Ganymede is the largest moon in the Solar System, and is even bigger than the"
"Jingpo Lacus Jingpo Lacus is a lake in the north polar region of Titan, the planet Saturn's largest moon. It and similarly sized Ontario Lacus are the largest known bodies of liquid on Titan after the three maria (Kraken Mare, Ligeia Mare and Punga Mare). It is composed of liquid hydrocarbons (mainly methane and ethane). It is west of Kraken Mare at 73° N, 336° W, roughly 240 km (150 mi) long, similar to the length of Lake Onega on Earth. Its namesake is Jingpo Lake, a scenic lake in China. On 8 July 2009, ""Cassini""'s Visual and Infrared Mapping"
"brightness and orbital elements. Although the images obtained by ""Voyager 2"" do not have a high enough resolution to allow surface features to be distinguished, ""Voyager 2"" was able to measure the size of Nereid and found that it was grey in colour and had a higher albedo than Neptune's other small satellites. In the Larry Niven book ""Ringworld"", Nereid is described as having been leased by the Outsiders ""half a millennium ago"". The protagonist, Louis Wu, speculates that the Outsiders evolved on a gas giant moon similar to Nereid. Nereid (moon) Nereid is the third-largest moon of Neptune. It"