- Larissa (moon)
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Larissa 
Two views of Larissa by Voyager 2DiscoveryDiscovered by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, and David J. Tholen Discovery date May 24, 1981 Epoch 18 August 1989 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)
Satellite of Neptune Physical characteristicsDimensions 216×204×168 km (± ~10 km)[2][3] Mean radius 97 ± 3 km[4] Volume ~3.5×106km³ Mass ~4.2×1018 kg (estimate)[a] Mean density ~1.2 g/cm³ (estimate)[4] Equatorial surface gravity ~0.03 m/s2[b] Escape velocity ~0.076 km/s[c] Rotation period synchronous Axial tilt zero Albedo 0.09[2][4] Temperature ~51 K mean (estimate) Apparent magnitude 21.5[4] - For the Greek city and other uses see Larissa (disambiguation)
Larissa (
/ləˈrɪsə/ lə-riss-ə; 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.Contents
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, 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
Map of Larissa
The fourth-largest satellite of Neptune, 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.
Notes
- ^ 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 Stooke (1994).[5]
- ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r: Gm/r2.
- ^ Escape velocity derived from the mass m, the gravitational constant G and the radius r: √2Gm/r.
References
- ^ 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.
- ^ a b Karkoschka, Erich (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162 (2): 400–407. Bibcode 2003Icar..162..400K. doi:10.1016/S0019-1035(03)00002-2.
- ^ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptuniansatfact.html. Retrieved 2008-12-13.
- ^ a b c d "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2010-10-18. http://ssd.jpl.nasa.gov/?sat_phys_par. Retrieved 2011-10-11.
- ^ Stooke, Philip J. (1994). "The surfaces of Larissa and Proteus". Earth, Moon, and Planets 65 (1): 31–54. Bibcode 1994EM&P...65...31S. doi:10.1007/BF00572198.
- ^ Reitsema, H. J.; Hubbard, W. B.; Lebofsky, L. A.; Tholen, D. J. (1982). "Occultation by a Possible Third Satellite of Neptune". Science 215 (4530): 289–291. Bibcode 1982Sci...215..289R. doi:10.1126/science.215.4530.289. PMID 17784355.
- ^ Marsden, Brian G. (May 29, 1981). "S/1981 N 1". IAU Circular 3608. http://www.cbat.eps.harvard.edu/iauc/03600/03608.html. Retrieved 2011-10-26.
- ^ Smith, B. A.; Soderblom, L. A. et al. (1989). "Voyager 2 at Neptune: Imaging Science Results". Science 246 (4936): 1422–1449. Bibcode 1989Sci...246.1422S. doi:10.1126/science.246.4936.1422. PMID 17755997. [on page 1435]
- ^ Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular 4824. http://www.cbat.eps.harvard.edu/iauc/04800/04824.html. Retrieved 2011-10-26.
- ^ Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular 5347. http://www.cbat.eps.harvard.edu/iauc/05300/05347.html. Retrieved 2011-10-26.
- ^ Banfield, Don; Murray, Norm (October 1992). "A dynamical history of the inner Neptunian satellites". Icarus 99 (2): 390–401. Bibcode 1992Icar...99..390B. doi:10.1016/0019-1035(92)90155-Z.
External links
- Larissa Profile by NASA's Solar System Exploration
- Neptune's Known Satellites (by Scott S. Sheppard)
Moons of Neptune Generally listed in increasing distance from NeptuneRegular (inner) Triton Irregular See also Neptune Discovery 
Characteristics - Rings
- Great Dark Spot
- Small Dark Spot
- The Scooter
- Kuiper belt
Moons Exploration Trojans Miscellaneous Categories:
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