Larissa

Identity and classification

Larissa is a moon of Neptune. NASA’s supplied evidence describes it as one of the small moons found near the planet’s faint ring system in 1989. Its nature as a natural satellite is also placed within NASA’s statement that Neptune has 16 known moons. That total characterizes the system as presented by the source; it does not provide a detailed dynamical classification or individual physical measurements for Larissa.

The available mission material explicitly places Larissa among the six new moons discovered by Voyager 2 during its Neptune encounter: Proteus, Larissa, Despina, Galatea, Thalassa, and Naiad. A Voyager fact sheet further says that the new Neptunian moons were small and remained close to Neptune’s equatorial plane. Their names were selected by the International Astronomical Union from mythological water deities. The evidence supplied here does not include the formal naming resolution or a more specific individual etymology for Larissa.

Discovery and observation

The year 1989 is the key observational date in the supplied record. NASA places Larissa’s finding near Neptune’s faint rings in that year, while the Voyager 2 mission page credits the spacecraft with discovering Larissa and five other moons, as well as four new rings. The connection between Larissa’s recognition and the Voyager 2 flyby is therefore directly supported. The sources do not provide an exact discovery date, an image sequence, the observing instrument, or the viewing geometry that allowed Larissa to be distinguished from the rings and planet.

Hubble observations provide a later visual context for apparent motion among the inner moons. In the cited image set, solid green lines trace each moon’s full orbit, and the spacing of moon images follows the interval between Hubble exposures. In that particular view, Larissa is listed after Proteus and before Galatea in the sequence of distance from Neptune. Larissa, Galatea, and Despina move clockwise in the image, unlike Triton’s retrograde counter-clockwise motion. This is explicitly a view-dependent image description, not a replacement for numerical inclination, period, or velocity data.

Shape, surface, and composition

NASA describes Larissa as irregularly shaped and heavily cratered. The wording establishes that it is not presented as an ideal sphere and that impact craters are a prominent observed surface characteristic. However, the available material does not quantify relief, crater numbers or sizes, geological-unit ages, impact distribution, fractures, deposits, or color variations. It also supplies no spectra or compositional measurements from which mineralogy or ice content could be established.

Accordingly, these sources cannot support claims about a differentiated crust, a structured interior, porosity, water ice, rock, or other constituents. Describing Larissa as small and cratered does not yield its mass, density, surface gravity, or ability to retain an atmosphere. Likewise, the absence of atmospheric information in the evidence does not itself prove that an extremely tenuous exosphere is absent; it means that no atmospheric detection or characterization is provided in this record.

Orbit, evolution, and environment

Larissa’s orbit is described as mostly circular. NASA additionally states that it is slowly spiraling inward, meaning that it is gradually approaching Neptune. This is the principal orbital-evolution information available, and its limits matter: no decay rate, quantified mechanism, orbital distance, numerical eccentricity, or timescale is supplied. A date for impact, disruption, or conversion into ring material therefore cannot be derived from the evidence provided.

Its location near the faint ring system is observationally important. Voyager 2 found four new rings during the encounter that also identified Larissa, but the supplied sources do not say that Larissa creates, confines, or perturbs any particular ring. They likewise provide no evidence for resonances, a ring of its own, associated dust, arcs, or subordinate satellites. The mention of other inner moons places it in a population near Neptune’s equatorial plane, but does not establish a specific interaction with any individual moon.

Rotation, origin, and open questions

No rotation period, spin-axis orientation, libration, or tidal-locking state is given for Larissa. A JPL page on planetary physical parameters notes updates to sidereal rotation periods and rotation rates for Saturn, Uranus, and Neptune; it concerns planets and does not furnish a rotational measurement for Larissa. Similarly, the supplied material cannot reconstruct how Larissa formed, whether it evolved from a different precursor, or the details of its collisional history beyond the observed heavily cratered appearance.

Larissa’s scientific importance in this evidence lies in its membership in Neptune’s small inner-moon population, its observed spatial association with faint rings, and the indication of slow orbital evolution. A careful account must separate direct statements—irregular shape, heavy cratering, a mostly circular orbit, slow inward spiraling, and appearances in Voyager and Hubble material—from what remains unknown. Its dimensions and physical properties, composition, internal structure, atmosphere, complete orbital parameters, rotation, age, origin, and the ultimate outcome of migration remain unresolved by these sources. This profile does not turn those uncertainties into facts.