View source for Astronomy:Naiad (moon)

{{Infobox planet
| name = Naiad
| image = Naiad Voyager.png
| caption = Naiad as seen by ''[[Astronomy:Voyager 2|Voyager 2]]'' (elongation is due to smearing)
| discoverer = Voyager Imaging Team
| discovered = September 1989
| mpc_name = Neptune III
| pronounced = {{IPAc-en|ˈ|n|eɪ|ə|d}} or {{IPAc-en|ˈ|n|aɪ|æ|d}},<ref>Noah Webster (1884) ''A Practical Dictionary of the English Language''</ref><ref>{{OED|naiad}}</ref><br />{{IPAc-en|ˈ|n|eɪ|ə|d}} or {{IPAc-en|ˈ|n|aɪ|ə|d}}<ref>{{MW|naiad}}</ref>
| adjectives = Naiadian {{IPAc-en|-|ˈ|æ|d|i|ə|n}}<ref>Morris (1904) ''British violin-makers''</ref>
| named_after = pl. Ναϊάδες ''Nāïades''
| orbit_ref = <ref name="Jacobson2004" /><ref name="Showalter2019" />
| epoch = 18 August 1989
| semimajor = 48 224.41 &nbsp;km
| eccentricity = 0.0047 ± 0.0018
| period = 0.2943958 ± 0.0000002 d
| avg_speed =
| inclination = {{unbulleted list | 4.75 ± 0.03° (to Neptune equator) | 4.75° (to local [[Astronomy:Laplace plane|Laplace plane]]) }}
| satellite_of = [[Astronomy:Neptune|Neptune]]
| dimensions = 96×60×52&nbsp;km<ref name="Karkoschka2003" /><ref name="Williams2008-nssdc" />
| mean_radius = 30.2 ± 3.2&nbsp;km<ref name="Showalter2019" />
| density = {{val|0.8|0.48|u=g/cm3}}<ref name="Brozovic2019"/>
| rotation = synchronous
| axial_tilt = zero
| albedo = 0.072<ref name="Karkoschka2003" /><ref name="jplssd" />
| magnitude = 23.91<ref name="jplssd" />
| single_temperature = ~51 [[Kelvin|K]] mean (estimate)
| note = no
}}
'''Naiad''' {{IPAc-en|ˈ|n|eɪ|ə|d}}, (also known as '''Neptune&nbsp;III''' and previously designated as '''S/1989 N 6''') named after the naiads of Greek legend,<ref name="USGS-Gazetteer" /> is the innermost satellite of [[Astronomy:Neptune|Neptune]] and the nearest to the center of any gas giant with moons with a distance of 48,224 km from the planet's center. Its orbital period is less than a Neptunian day, resulting in tidal dissipation that will cause its orbit to decay. Eventually it will either crash into Neptune's atmosphere or break up to become a new ring.<ref>{{cite web |title=Naiad |url=https://solarsystem.nasa.gov/moons/neptune-moons/naiad/in-depth/ |website=NASA Science Solar System Exploration |publisher=NASA}}</ref>{{short description|Moon of Neptune}}

==History==
[[File:Simulated view of Naiad.jpg|thumb|left|210px|[[Computer simulation|Simulated]] view of Naiad|alt=]]
Naiad was discovered sometime before mid-September 1989 from the images taken by the ''[[Astronomy:Voyager 2|Voyager 2]]'' [[Engineering:Space probe|probe]]. The last moon to be discovered during the flyby, it was designated '''S/1989&nbsp;N&nbsp;6'''.<ref name="IAUC 4867" /> The discovery was announced on 29 September 1989, in the IAU Circular No. 4867, and mentions "25 frames taken over 11 days", implying a discovery date of sometime before 18 September. The name was given on 16 September 1991.<ref name="IAUC 5347" />

==Physical characteristics==
Naiad is irregularly shaped. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from [[Astronomy:Triton (moon)|Triton]] soon after that moon's capture into a very eccentric initial orbit.<ref name="BanfieldMurray1992" />

== Orbit ==
[[File:Naiad-Thalassa 73-69 orbital resonance.jpg|thumb|left|210px|Depiction of Naiad's orbital motion (red) in a view that co-rotates with Thalassa (central yellow dot)|alt=]]
Naiad is in a 73:69 orbital resonance with the next outward moon, [[Astronomy:Thalassa (moon)|Thalassa]], in a "dance of avoidance". As it orbits Neptune, the more inclined Naiad successively passes Thalassa twice from above and then twice from below, in a cycle that repeats every ~21.5 Earth days. The two moons are about 3540 km apart when they pass each other. Although their orbital radii differ by only 1850 km, Naiad swings ~2800 km above or below Thalassa's orbital plane at closest approach. Thus this resonance, like many such orbital correlations, serves to stabilize the orbits by maximizing separation at conjunction. However, the role of orbital inclination in maintaining this avoidance in a case where eccentricities are minimal is unusual.<ref name="JPLnews2019" /><ref name="Brozovic2019" />

==Exploration==
Since the ''Voyager 2'' flyby, the Neptune system has been extensively studied from ground-based [[Astronomy:Observatory|observatories]] and the [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]] as well. In 2002–03 the [[Astronomy:W. M. Keck Observatory|Keck telescope]] observed the system using [[Astronomy:Adaptive optics|adaptive optics]] and detected easily the largest four inner satellites. [[Astronomy:Thalassa (moon)|Thalassa]] was found with some image processing, but Naiad was not located.<ref name="Marchis2004May-AAS" /> Hubble has the ability to detect all the known satellites and possible new satellites even dimmer than those found by ''Voyager 2''. On 8 October 2013 the SETI Institute announced that Naiad had been located in archived Hubble imagery from 2004.<ref>{{cite web|title=Lost Neptune Moon Re-Discovered|url=http://news.discovery.com/space/astronomy/lost-neptune-moon-found-131008.htm|access-date=9 October 2013}}</ref> The suspicion that the loss of positioning was due to considerable errors in Naiad's [[Astronomy:Ephemeris|ephemeris]]<ref name="Showalter2005Aug-AAS" /> proved correct as Naiad was ultimately located 80 degrees from its expected position.

== References ==
{{reflist
| refs =

<ref name="Jacobson2004">
{{cite journal| doi = 10.1086/423037| last1 = Jacobson | first1 = R. A.| last2 = Owen | first2 = W. M. Jr.| year = 2004| pages = 1412–1417| title = The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations| journal = Astronomical Journal| volume = 128| issue = 3| bibcode = 2004AJ....128.1412J| doi-access = free}}
</ref>

<ref name="Karkoschka2003">
{{cite journal| doi = 10.1016/S0019-1035(03)00002-2| last = Karkoschka| first = E.| year = 2003| title = Sizes, shapes, and albedos of the inner satellites of Neptune| journal = Icarus| volume = 162| issue = 2| pages = 400–407| bibcode = 2003Icar..162..400K}}
</ref>

<ref name="Williams2008-nssdc">
{{cite web
| last = Williams
| first = D. R.
| date = 2008-01-22
| title = Neptunian Satellite Fact Sheet
| publisher = [[Organization:NASA|NASA]] (National Space Science Data Center)
| url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptuniansatfact.html
| access-date = 2008-12-13
}}
</ref>

<ref name="jplssd">
{{cite web
| title = Planetary Satellite Physical Parameters
| date = 2008-10-24
| publisher = [[Organization:JPL|JPL]] (Solar System Dynamics)
| url = http://ssd.jpl.nasa.gov/?sat_phys_par
| access-date = November 15, 2019
}}
</ref>

<ref name="USGS-Gazetteer">
{{cite web
| title = Planet and Satellite Names and Discoverers
| work = Gazetteer of Planetary Nomenclature
| publisher = USGS Astrogeology
| date = July 21, 2006
| url = http://planetarynames.wr.usgs.gov/append7.html
| access-date = 2006-08-05
}}
</ref>

<ref name="IAUC 4867">
{{cite journal
| last = Green
| first = D. W. E.
| title = Neptune
| date = September 29, 1989
| journal = IAU Circular
| volume = 4867
| url = http://www.cbat.eps.harvard.edu/iauc/04800/04867.html
| access-date = 2011-10-26
}}
</ref>

<ref name="IAUC 5347">
{{cite journal
| last = Marsden
| first = B. G.
| title = Satellites of Saturn and Neptune
| date = September 16, 1991
| journal = IAU Circular
| volume = 5347
| url = http://www.cbat.eps.harvard.edu/iauc/05300/05347.html
| access-date = 2011-10-26
}}
</ref>

<ref name="BanfieldMurray1992">
{{cite journal| doi = 10.1016/0019-1035(92)90155-Z| last1 = Banfield| first1 = D.| last2 = Murray| first2 = N.| date=October 1992 | title = A dynamical history of the inner Neptunian satellites| journal = Icarus| volume = 99| issue = 2| pages = 390–401| bibcode = 1992Icar...99..390B}}
</ref>

<ref name="Marchis2004May-AAS">
{{cite conference
| last1 = Marchis
| first1 = F.
| last2 = Urata
| first2 = R.
| last3 = de Pater
| first3 = I.
| last4 = Gibbard
| first4 = S.
| last5 = Hammel
| first5 = H. B.
| last6 = Berthier
| first6 = J.
| date = May 2004
| title = Neptunian Satellites observed with Keck AO system
| book-title = American Astronomical Society, DDA meeting #35, #07.08; Bulletin of the American Astronomical Society
| volume = 36
| page = 860
| bibcode = 2004DDA....35.0708M
}}
</ref>

<ref name="Showalter2005Aug-AAS">
{{cite conference
| last1 = Showalter
| first1 = M. R.
| last2 = Lissauer
| first2 = J. J.
| last3 = de Pater
| first3 = I.
| date = August 2005
| title = The Rings of Neptune and Uranus in the Hubble Space Telescope
| book-title = American Astronomical Society, DPS meeting #37, #66.09; Bulletin of the American Astronomical Society
| volume = 37
| page = 772
| bibcode = 2005DPS....37.6609S
}}
</ref>

<ref name="Showalter2019">{{cite journal|last1= Showalter|first1=M. R.|last2=de Pater|first2= I.|last3= Lissauer|first3=J. J.|last4= French|first4=R. S.|url=https://www.spacetelescope.org/static/archives/releases/science_papers/heic1904/heic1904a.pdf|title= The seventh inner moon of Neptune|journal= Nature|volume= 566|issue= 7744|year= 2019|pages= 350–353|doi= 10.1038/s41586-019-0909-9|pmid=30787452|pmc=6424524|bibcode=2019Natur.566..350S}}
</ref>

<ref name="JPLnews2019">
{{cite web
|url = https://www.jpl.nasa.gov/news/news.php?feature=7540
<!--http://spaceref.com/neptune/two-of-neptune-moons-are-locked-in-a-dance-of-avoidance.html-->
|title = NASA Finds Neptune Moons Locked in 'Dance of Avoidance'
|author = <!--Not stated--> 
|date = November 14, 2019
|website = Jet Propulsion Laboratory
|access-date = November 15, 2019
}} </ref>

<ref name="Brozovic2019">
{{cite journal
|last1 = Brozović
|first1 = M.
|last2 = Showalter
|first2 = M. R.
|last3 = Jacobson
|first3 = R. A.
|last4 = French
|first4 = R. S.
|last5 = Lissauer
|first5 = J. J.
|last6 = de Pater
|first6 = I.
|title = Orbits and resonances of the regular moons of Neptune
|date = October 31, 2019 
|journal = Icarus
|volume = 338
|issue = 2
|page = 113462
|arxiv = 1910.13612
|doi = 10.1016/j.icarus.2019.113462
|bibcode = 2020Icar..33813462B
|s2cid = 204960799
}} </ref>

}}

== External links ==
* [https://web.archive.org/web/20070801204452/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Nep_Naiad Naiad Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://web.archive.org/web/20081221181025/http://www.dtm.ciw.edu/sheppard/satellites/nepsatdata.html Neptune's Known Satellites] (by [[Biography:Scott S. Sheppard|Scott S. Sheppard]])
* [https://web.archive.org/web/20131012190515/http://www.seti.org/seti-institute/press-release/archival-hubble-images-reveal-neptunes-lost-inner-moon Archival Hubble Images Reveal Neptune's "Lost" Inner Moon] (SETI : October 8, 2013)
* {{YouTube
|id=WEsiSZtIDyI
|title=Neptune Moon Dance (animation)}} from NASA Jet Propulsion Laboratory


{{Moons of Neptune}}
{{Solar System moons (compact)}}
{{Neptune}}

{{DEFAULTSORT:Naiad (Moon)}}
[[Category:Moons of Neptune]]

{{Sourceattribution|Naiad (moon)}}