Larissa, also known as Neptune VII, is the fifth-closest inner satellite of

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

. It is named after

Larissa Larissa (; , , ) is the capital and largest city of the Thessaly region in Greece. It is the fifth-most populous city in Greece with a population of 148,562 in the city proper, according to the 2021 census. It is also the capital of the Larissa ...

, a lover of

Poseidon Poseidon (; ) is one of the twelve Olympians in ancient Greek religion and mythology, presiding over the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 He was the protector of seafarers and the guardian of many Hellenic cit ...

(the Greek equivalent of the

Roman god Roman mythology is the body of myths of ancient Rome as represented in the Latin literature, literature and Roman art, visual arts of the Romans, and is a form of Roman folklore. "Roman mythology" may also refer to the modern study of these ...

). Larissa is also the eponymous

nymph A nymph (; ; sometimes spelled nymphe) is a minor female nature deity in ancient Greek folklore. Distinct from other Greek goddesses, nymphs are generally regarded as personifications of nature; they are typically tied to a specific place, land ...

of the

city A city is a human settlement of a substantial size. The term "city" has different meanings around the world and in some places the settlement can be very small. Even where the term is limited to larger settlements, there is no universally agree ...

Thessaly Thessaly ( ; ; ancient Aeolic Greek#Thessalian, Thessalian: , ) is a traditional geographic regions of Greece, geographic and modern administrative regions of Greece, administrative region of Greece, comprising most of the ancient Thessaly, a ...

Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

Discovery

Larissa was first discovered by

Harold J. Reitsema Harold James Reitsema (born January 19, 1948) is an American astronomer who was part of the teams that discovered Larissa (moon), Larissa, the fifth of Moons of Neptune, Neptune's known moons, and Telesto (moon), Telesto, Moons of Saturn, Saturn ...

, William B. Hubbard, Larry A. Lebofsky and David J. Tholen, based on fortuitous ground-based stellar

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

observations on May 24, 1981. It was given the temporary

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calcu ...

S/1981 N 1 and its supposed existence was announced on May 29, 1981. The moon was later recovered and confirmed to be the only object in its

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

during the ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants (Jupiter and Saturn) and enabled further encounters with the ice giants (Uranus and ...

'' flyby in 1989 after which it received the additional designation S/1989 N 2 on August 2, 1989. The announcement by

Stephen P. Synnott Stephen P. Synnott (born 1946) is an American astronomer and Voyager scientist at JPL, and expert in spacecraft optical navigation techniques. He has discovered several natural satellites of outer Solar System planets such as Metis, Puck, Lari ...

spoke of "10 frames taken over 5 days", which gives a recovery date sometime before July 28. The name was given and then confirmed by the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

on September 16, 1991.

Characteristics

Larissa is the fourth-largest satellite of Neptune. It is irregular (non-spherical) in shape and appears to be heavily cratered, with no sign of any geological modification. It is likely that Larissa, like the other satellites inward of

Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus' ...

, is a

rubble pile In astronomy, a rubble pile is a celestial body that consists of numerous pieces of debris that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the various chunks that make the ...

re-accreted from fragments of Neptune's original satellites, which were disrupted by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit. Larissa's orbit is nearly circular and lies below Neptune's

synchronous orbit A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. Simplified meani ...

radius, which means it is slowly spiralling inward due to

tidal deceleration Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon) and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit (satel ...

and may eventually impact Neptune's atmosphere, or break up into a

planetary ring A ring system is a disc or torus orbiting an astronomical object that is composed of solid material such as dust, meteoroids, planetoids, moonlets, or stellar objects. Ring systems are best known as planetary rings, common components of sate ...

upon passing its

Roche limit In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal force ...

due to tidal stretching, similarly to how

will eventually collide with

or break into a

. Compositionally, Larissa appears to be similar to other small inner Neptunian satellites, with a deep 3.0 micron feature attributed to water ice or hydrated silicate minerals. It has a 0.08 albedo at 1.4 and 2.0 microns, dropping to 0.03 at 3.0 microns, and increasing to 0.09 at 4.6 microns.

Exploration

Larissa has only been visited once by ''

'' in 1989. The probe was able to get some photographs with details of Larissa, showing its cratered surface; unlike the other inner moons of Neptune that only appeared as dots or smudges.

Notes

References

External links

Larissa Profile
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NASA's Solar System Exploration

(by Scott S. Sheppard) {{DEFAULTSORT:Larissa (Moon) Moons of Neptune 19810524 M