 Two views of Larissa by Voyager 2 | |
| Discovery | |
|---|---|
| Discovered by | Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, and David J. Tholen |
| Discovered on | May 24, 1981 |
| Orbital characteristics[1] | |
| | |
| 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 | 216×204×168 km (± ~10 km)[2][3] |
| Mean radius | 97 ± 3 km[4] |
| Mass | ~4.2 × 1018 kg (estimate)[5] |
| Mean density | ~1.2 g/cm3 (estimate) |
| Rotation period | assumed synchronous |
| Axial tilt | ~zero presumably |
| Albedo (geometric) | 0.09[2][3][4] |
| Surface temp. | ~51 K mean (estimate) |
| Atmosphere | none |
- There are also asteroidss 1162 Larissa, and the paronymous 302 Clarissa.
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.
Discovery
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]
Characteristics
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.
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