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Larissa (moon)
From Wikipedia, the free encyclopedia
 Two views of Larissa by Voyager 2 |
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| Discovery | |
|---|---|
| Discovered by | Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, and David J. Tholen |
| Discovered on | May 24, 1981 |
| Orbital characteristics[1] | |
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|
|
| Semi-major axis | 73.548 ± 1 km |
| Eccentricity | 0.001393 ± 0.00008 |
| Orbital period | 0.55465332 ± 0.00000001 d |
| Inclination | 0.251 ± 0.009° (to Neptune equator) 0.205° (to local Laplace plane) |
| Is a satellite of | Neptune |
| Physical characteristics | |
| Dimensions | 216×204×164 km (± ~10 km)[2] |
| Mass | ~4.2×1018 kg (estimate)[3] |
| Mean density | ~1.2 g/cm3 (estimate) |
| Rotation period | assumed synchronous |
| Axial tilt | ~zero presumably |
| Albedo (geometric) | 0.09[2] |
| Surface temp. | ~51 K mean (estimate) |
| Atmosphere | none |
- There are also asteroids 1162 Larissa, and the paronymous 302 Clarissa.
Larissa (lə-ris'-ə, IPA: /ləˈrɪsə/, Greek Λάρισσα), or Neptune VII, is the fifth closest inner satellite of Neptune. It is named after Larissa, a lover of Poseidon (Neptune) in Greek mythology.
Contents |
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[4] on May 24, 1981, and given the temporary designation S/1981 N 1 and announced on 29 May 1981.[5] The moon was recovered and confirmed to be the only object in its orbit during the Voyager 2 flyby in 1989[6] after which it received the additional designation S/1989 N 2 on August 2, 1989.[7] 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.[8]
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.[9]
Larissa's orbit lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
- ^ 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.
- ^ a b E. Karkoschka (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162: 400.
- ^ 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.
- ^ H.J. Reitsema et al (1982). "Occultation by a possible third satellite of Neptune". Science 215: 289-291.
- ^ IAU Circular 3608 describing the discovery of S/1981 N 1
- ^ B.A. Smith et al (1989). "Votager 2 at Neptune: Imaging Science Results". Science 246: 1422. [on page 1435]
- ^ IAU Circular 4824 describing the discovery of S/1989 N 2, 3, and 4
- ^ IAU Circular No. 5347 (September 16 1991). Retrieved on 2007-04-10.
- ^ D. Banfield and N. Murray (1992). "A dynamical history of the inner neptunian satellites". Icarus 99: 390.
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| Generally listed in increasing distance from Neptune. |
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|---|---|---|
| Moons | Naiad · Thalassa · Despina · Galatea · Larissa · Proteus · Triton · Nereid · Halimede · Sao · Laomedeia · Psamathe · Neso |  |
| Characteristics | Rings of Neptune · Great Dark Spot | |
| Discovery | John Couch Adams · Johann Gottfried Galle · William Lassell · Urbain Le Verrier | |
| Exploration | Voyager program · Voyager 2 | |
| Neptune Trojans | 2001 QR322 · 2004 UP10 · 2005 TN53 · 2005 TO74 · 2006 RJ103 · 2007 RW10 | |
| Other | Neptune-crosser asteroid · Neptune in fiction | |