Larissa was first discovered by
Harold J. Reitsema,
William B. Hubbard,
Larry A. Lebofsky and
David J. Tholen, based on fortuitous ground-based stellar
occultation observations[14] on May 24, 1981. It was given the temporary
provisional designationS/1981 N 1 and its supposed existence was announced on May 29, 1981.[15] The moon was later recovered and confirmed to be the only object in its
orbit during the Voyager 2 flyby in 1989[16] after which it received the additional designation S/1989 N 2 on August 2, 1989.[17] The announcement by
Stephen P. Synnott 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 on September 16, 1991.[18]
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, is a
rubble pilere-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.[19]
Larissa has only been visited once by Voyager 2.[20] 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
^A volume of (3.5±1.0)×106 km3 was obtained from a detailed shape model, assuming dimensions of 208 km × 192 km × 178 km.[10] The long and short dimensions were estimated based on a single image, with the medium dimension assumed as halfway between those values.[11] The volume has been scaled according to more recently obtained dimensions of 216 km × 204 km × 168 km based on two images.[8]
^A density of 0.05–1.5 g/cm3 was calculated by approximating the volume as a sphere with a radius of 97±3 km.[12] The mass was calculated with the provided density and the assumed volume.
^Density obtained from the calculated mass and the calculated volume.
^
Jacobson, R. A.; Owen, W. M. Jr. (2004). "The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations". Astronomical Journal. 128 (3): 1412–1417.
Bibcode:
2004AJ....128.1412J.
doi:
10.1086/423037.
S2CID121398325.