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Larissa (pronounced /ləˈrɪsə/ lə-RISS-ə, or as in Greek Λάρισα), also known as Neptune VII, is the fifth closest inner satellite of Neptune. It is named after Larissa, a lover of Poseidon (Neptune) in Greek mythology and eponymous nymph of the city in Thessaly.


It 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[6] on May 24, 1981, and given the temporary designation S/1981 N 1 and announced on 29 May 1981.[7] The moon was recovered and confirmed to be the only object in its orbit during the Voyager 2 flyby in 1989[8] after which it received the additional designation S/1989 N 2 on August 2, 1989.[9] 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 on 16 September 1991.[10]

Map of Larissa

Larissa is irregular (non-spherical) in shape and appears to be heavily cratered, with no sign of any geological modification. Little else is known about it. It is likely that Larissa, like the other satellites inward of Triton, is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.[11]

Larissa's orbit is circular but not perfect and lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.


1. ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r: Gm/r2.
2. ^ Escape velocity derived from the mass m, the gravitational constant G and the radius r: √2Gm/r.


1. ^ R.A. Jacobson and W.M. Owen Jr. (2004). "The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations". Astronomical Journal 128: 1412. doi:10.1086/423037.
2. ^ a b E. Karkoschka (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162: 400. doi:10.1016/S0019-1035(03)00002-2.
3. ^ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-13.
4. ^ a b c d "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-13.
5. ^ The mass estimate is based on the assumed density of 1.2 g/cm³, and a volume of 3.5 × 106 km³ obtained from a detailed shape model in P.J. Stooke (1994). "The surfaces of Larissa and Proteus". Earth, Moon ad Planets 65: 31. doi:10.1007/BF00572198.
6. ^ H.J. Reitsema et al. (1982). "Occultation by a possible third satellite of Neptune". Science 215 (4530): 289–291. doi:10.1126/science.215.4530.289. PMID 17784355.
7. ^ IAU Circular 3608 describing the discovery of S/1981 N 1
8. ^ B.A. Smith et al. (1989). "Votager 2 at Neptune: Imaging Science Results". Science 246 (4936): 1422. doi:10.1126/science.246.4936.1422. PMID 17755997. [on page 1435]
9. ^ IAU Circular 4824 describing the discovery of S/1989 N 2, 3, and 4
10. ^ "IAU Circular No. 5347". September 16, 1991. Retrieved 2007-04-10.
11. ^ D. Banfield and N. Murray (1992). "A dynamical history of the inner neptunian satellites". Icarus 99: 390. doi:10.1016/0019-1035(92)90155-Z.

A simulated view of Larissa orbiting Neptune. The surface details are fictional.

External links

* Larissa Profile by NASA's Solar System Exploration
* Neptune's Known Satellites (by Scott S. Sheppard)

* Neptune's Known Satellites (by Scott S. Sheppard)

Moons of Neptune

see also: The Solar System

Astronomy Encyclopedia

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