Larissa (moon)

Short description: Moon of Neptune

Larissa

Larissa from Voyager 2

Discovery
Discovered by| Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, and David J. Tholen[1]
Discovery date| May 24, 1981
Designations

Designation

| Neptune VII
Pronunciation| /ləˈrɪsə/[2]
Named after| Λάρισσα Lārissa

Alternative names

| S/1989 N 2 S/1981 N 1
Adjectives| Larissean,[3] Larissan,[4] Larissian[5] /ləˈrɪs(i)ən/
Orbital characteristics[6][7]
Epoch 18 August 1989

Semi-major axis

| 73 548.26 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 characteristics
Dimensions| 216 × 204 × 168 km (± ~10 km)[8][9]
Mean radius| 97 ± 5.4 km[7]
Surface area| 118,236.98 km2[10]
Volume| ~3.5×106 km³
Mass| ~4.2×1018 kg (estimate)[lower-alpha 1]
Mean density| ~1.2 g/cm3 (estimate)[12]

surface gravity

| ~0.03 m/s2[lower-alpha 2]

escape velocity

| ~0.076 km/s[lower-alpha 3]
Rotation period| synchronous
Axial tilt| zero
Albedo| 0.09[8][12]
Physics| ~51 K mean (estimate)
Apparent magnitude| 21.5[12]

Larissa, 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, Greece.

## Contents

* 1 Discovery
* 2 Characteristics
* 3 Exploration
* 4 Notes
* 5 References
* 6 External links

## 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[13] on May 24, 1981, given the temporary designation S/1981 N 1 and announced on May 29, 1981.[14] The moon was recovered and confirmed to be the only object in its orbit during the Voyager 2 flyby in 1989[15] after which it received the additional designation S/1989 N 2 on August 2, 1989.[16] 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 September 16, 1991.[17]

## Characteristics

Side-by-side comparison of Larissa imaged by Voyager 2 and an enhanced version to the right

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. 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 disrupted by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.[18]

Larissa's orbit is nearly circular 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, similarly to how Triton will eventually collide with Neptune or break into a planetary ring.

## Exploration

Map of Larissa

Larissa has only been visited by Voyager 2.[19] The probe was able to get photographs of Larissa, showing its cratered surface.

## Notes

1. ↑ 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).[11]
2. ↑ Surface gravity derived from the mass m, the gravitational constant G and the radius r: Gm/r2.
3. ↑ Escape velocity derived from the mass m, the gravitational constant G and the radius r: √2Gm/r.

## References

1. ↑ "Larissa In Depth". https://solarsystem.nasa.gov/moons/neptune-moons/larissa/in-depth/.
2. ↑ "Larissa". Merriam-Webster Dictionary. https://www.merriam-webster.com/dictionary/Larissa.
3. ↑ Boccaccio (1974) The book of Theseus
4. ↑ Livy (1850 trans.) The history of Rome, v. 3
5. ↑ Bell (1790) Bell's New pantheon
6. ↑ 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. doi:10.1086/423037. Bibcode: 2004AJ....128.1412J.
7. ↑ 7.0 7.1 Showalter, M. R.; de Pater, I.; Lissauer, J. J.; French, R. S. (2019). "The seventh inner moon of Neptune". Nature 566 (7744): 350–353. doi:10.1038/s41586-019-0909-9. PMID 30787452. PMC 6424524. Bibcode: 2019Natur.566..350S. https://www.spacetelescope.org/static/archives/releases/science_papers/heic1904/heic1904a.pdf.
8. ↑ 8.0 8.1 Karkoschka, Erich (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162 (2): 400–407. doi:10.1016/S0019-1035(03)00002-2. Bibcode: 2003Icar..162..400K.
9. ↑ 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.
10. ↑ "Larissa In Depth". https://solarsystem.nasa.gov/moons/neptune-moons/larissa/by-the-numbers/.
11. ↑ Stooke, Philip J. (1994). "The surfaces of Larissa and Proteus". Earth, Moon, and Planets 65 (1): 31–54. doi:10.1007/BF00572198. Bibcode: 1994EM&P...65...31S.
12. ↑ 12.0 12.1 12.2 "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2010-10-18. http://ssd.jpl.nasa.gov/?sat_phys_par.
13. ↑ Reitsema, Harold J.; Hubbard, William B.; Lebofsky, Larry A.; Tholen, David J. (1982). "Occultation by a Possible Third Satellite of Neptune". Science 215 (4530): 289–291. doi:10.1126/science.215.4530.289. PMID 17784355. Bibcode: 1982Sci...215..289R.
14. ↑ 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.
15. ↑ Smith, B. A.; Soderblom, L. A.; Banfield, D.; Barnet, C.; Basilevsky, A. T.; Beebe, R. F.; Bollinger, K.; Boyce, J. M. et al. (1989). "Voyager 2 at Neptune: Imaging Science Results". Science 246 (4936): 1422–1449. doi:10.1126/science.246.4936.1422. PMID 17755997. Bibcode: 1989Sci...246.1422S. https://zenodo.org/record/1230992. [on page 1435]
16. ↑ 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.
17. ↑ 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.
18. ↑ Banfield, Don; Murray, Norm (October 1992). "A dynamical history of the inner Neptunian satellites". Icarus 99 (2): 390–401. doi:10.1016/0019-1035(92)90155-Z. Bibcode: 1992Icar...99..390B.
19. ↑ "Larissa Facts". https://www.factsjustforkids.com/planet-facts/neptune-facts-for-kids/larissa-moon-facts.html.

## External links

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

* v
* t
* e

Moons of Neptune

Generally listed in increasing distance from Neptune

Regular (inner)|

* Naiad
* Thalassa
* Despina
* Galatea
* Larissa
* Hippocamp
* Proteus

Triton|

* Triton (Atmosphere
* Geological features
* Sky)

Irregular|

* Nereid
* Halimede
* Sao
* Laomedeia
* Psamathe
* Neso

See also|

* Neptune trojans
* Rings of Neptune

* Book
* Category
* Portal

* v
* t
* e

Natural satellites of the Solar System

Planetary
satellites|

* Terrestrial
* Martian
* Jovian
* Saturnian
* Uranian
* Neptunian

Dwarf-planet
satellites|

* Plutonian
* Haumean
* Makemakean
* Eridian
* OR10
* Quaoaran
* Orcean

Minor-planet moons|

* Main belt binaries:
* Antiope
* Frostia
* Berna
* Tokai
* Ostro
* Balam
* Doppler
* Pauling
* Iwamoto
* Wolff
* Bettig
* Christophedumas
* Trojans:
* Patroclus–Menoetius
* Hektor–Skamandrios
* Iphthime
* Eurydamas
* TNOs:
* Huya
* Typhon–Echidna
* Lempo–Paha–Hiisi
* 2002 UX25
* Logos–Zoe
* Ceto–Phorcys
* Borasisi–Pabu
* Sila–Nunam
* Teharonhiawako–Sawiskera
* Salacia–Actaea
* 2002 WC19
* Altjira
* Varda–Ilmarë
* 2003 AZ84
* Gǃkúnǁʼhòmdímà–Gǃòʼé ǃHú
* Mors–Somnus
* Manwë–Thorondor
* ǂKá̦gára–ǃHãunu
* 2013 FY27

Ranked by size|

* Planetary-mass moon
* Ganymede
* largest: 5268 km / 0.413 Earths
* Titan
* Callisto
* Io
* Moon
* Europa
* Triton
* Titania
* Rhea
* Oberon
* Iapetus
* Charon
* Umbriel
* Ariel
* Dione
* Tethys
* Dysnomia
* Enceladus
* Miranda
* Vanth
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* Mimas
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* ...

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* v
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Neptune

* Outline of Neptune

Geography|

* Great Dark Spot
* Small Dark Spot
* Rings

NASA image of Neptune

Moons|

* Despina
* Galatea
* Halimede
* Hippocamp
* Laomedeia
* Larissa
* Naiad
* Nereid
* Neso
* Proteus
* Psamathe
* Sao
* Thalassa
* Triton

Astronomy|

| Discovery|

* Urbain Le Verrier
* Johann Gottfried Galle
* John Couch Adams
* Heinrich Louis d'Arrest
* William Lassell

|

General|

* Kuiper belt
* Neptune-crossing minor planets

Trojans|

* 2001 QR322
* 2004 KV18
* 2004 UP10
* 2005 TN53
* 2005 TO74
* 2006 RJ103
* (527604) 2007 VL305
* 2008 LC18
* 2011 HM102

Exploration|

| Past|

* Voyager 2 (1989 flyby)

|

Proposals|

* ODINUS
* Triton Hopper
* Argo
* Trident

Cancelled|

* Mariner Mark II
* Neptune Orbiter
* New Horizons 2

Related|

* Fiction
* Mythology

* Book
* Category
* Portal

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