Pan (moon): Difference between revisions

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{{short description|Moon of Saturn}}

{|class="toccolours" style="margin-left: 1em; float: right; border: 1px solid #CCC"

{{for multi|the moon of Jupiter|Carme (moon)|other uses|Pan (disambiguation)}}

|-

{{Use dmy dates|date=March 2017}}

! colspan="2" | [[Image:Pan_Rev09.2x.jpg]]<br/><small>Pan in the center of the image,<br/>occupying the Encke Division in Saturn's rings</small>

{{Infobox planet

|-

| name = Pan

! bgcolor="#a0ffa0" colspan="2" | Discovery

| image = Pan color PIA21449.png

|-

| image_scale =

! align="left" | Discovered by

| caption = Color photo of Pan by ''Cassini'' in March 2017{{efn|This color photo of Pan was created by combining separate photos taken in infrared, green, and ultraviolet spectral filters of the ''[[Cassini-Huygens|Cassini]]'' spacecraft's narrow-angle Imaging Science Subsystem (ISS) camera on 7 March 2017. This view of the moon's northern hemisphere shows its [[walnut]]-like appearance, with a highly inclined equatorial ridge almost eclipsing the moon's southern hemisphere from view.}}

| [[Mark R. Showalter|M. R. Showalter]]

| discovered = July 16, 1990

|-

| pronounced = {{IPAc-en|ˈ|p|æ|n}}

! align="left" | Discovered in

| named_after = [[Pan (mythology)|Πάν]] ''Pān<!--the 'a' is long in Greek, as reflected in the Latin, even if not written in Greek-->''

| [[July 16]], [[1990]]

| mpc_name = Saturn XVIII

|-

| alt_names = S/1981 S 13

! bgcolor="#a0ffa0" colspan="2" | [[Orbit]]al characteristics <ref name="Spitale06">{{cite journal | author= J.N. Spitale et al| title= ''The orbits of Saturn's small satellites derived from combined historic and ''Cassini'' imaging observations''| journal= The Astronomical Journal| year= 2006| volume= 132| pages= 692| url= http://www.journals.uchicago.edu/AJ/journal/issues/v132n2/205235/205235.web.pdf}}</ref>

| adjectives = Pandean {{IPAc-en|p|æ|n|ˈ|d|iː|ə|n}}<ref>{{OED|Pandean}}</ref>

|-

| discoverer = [[Mark R. Showalter|M. R. Showalter]]

! align="left" | [[Semimajor axis]]

| orbit_ref = <ref name="Jacobson2008">{{cite journal | author= Jacobson, R. A. | display-authors= etal| title= Revised orbits of Saturn's small inner satellites| journal=[[Astronomical Journal]]| date= 2008| volume= 135 | issue= 1| pages= 261–263| bibcode=2008AJ....135..261J | doi= 10.1088/0004-6256/135/1/261| citeseerx= 10.1.1.653.3917| s2cid= 122998668}}</ref>

| 133,584.0±0.1 [[kilometer|km]]

| semimajor = {{val|133584.0|0.1|u=km}}

|-

| eccentricity = {{val|0.0000144|0.0000054}}

! align="left" | [[Eccentricity (orbit)|Eccentricity]]

| period = {{val|0.575050718|u=days}} ({{val|13.801217|u=hours}})

| 0.000035±0.000007

| inclination = {{val|0.0001|0.0004|u=°}}

|-

| satellite_of = [[Saturn]]

! align="left" | [[Orbital period]]

| group = [[Shepherd moon]] of the [[Encke Gap]]

| 0.575050718 d

| dimensions = {{val|34.6|x|28.2|x|21.0}}&nbsp;km<br/>(±&nbsp;{{val|0.4|x|0.4|x|1.0}}&nbsp;km)<ref name="Thomas2020"/>{{rp|page=2}}

|-

| mean_diameter = {{val|27.4|0.6|u=km}}<ref name="Thomas2020"/>{{rp|page=2}}

! align="left" | [[Inclination]]</br>(to Saturn's equator)

| volume = {{val|10748|u=km3}}<ref name="Thomas2020"/>{{rp|page=8}}

| 0.0010±0.0006°

| mass = {{val|4.30|0.22|e=15|u=kg}}<ref name="Thomas2020"/>{{rp|page=3}}

|-

| density = {{val|0.400|0.031|u=g/cm3}}<ref name="Thomas2020"/>{{rp|page=3}}

! align="left" | Is a [[natural satellite|satellite]] of

| surface_grav = {{val|0.0111|-|0.0169|u=m/s2}}<ref name="Thomas2020"/>{{rp|page=3}}

| [[Saturn (planet)|Saturn]]

| escape_velocity = {{V2|4.30e-6|17.3|3}}&nbsp;km/s at longest axis<br/>to {{V2|4.30e-6|10.5|3}}&nbsp;km/s at poles<!-- V2 template uses mass in terms of e+21 kg, radius in terms of km, and number of decimal places -->

|-

| rotation = [[synchronous rotation|synchronous]]

! bgcolor="#a0ffa0" colspan="2" | Physical characteristics

| axial_tilt = zero

|-

| albedo = 0.5

! align="left" | Mean [[diameter]]

| single_temperature = ≈&thinsp;78 K

| 30 km (35 × 35 × 23 km) <ref name="Porco06">{{cite journal | author= C.C. Porco et al.| title= ''Physical characteristics and possible accretionary origins for Saturn's small satellites''| journal= Bulletin of the American Astronomical Society| year= 2006| volume= 37| pages= 768| url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2289.pdf}}</ref>

}}

|-

! align="left" | [[Mass]]

| 4.9 ± 0.7 {{e|15}} [[kilogram|kg]] <ref name="Porco06"/>

|-

! align="left" | Mean [[density]]

| 0.36 ± 0.16 g/cm³

|-

! align="left" | Surface [[gravity]]

| 0.001 [[Acceleration|m/s²]]

|-

! align="left" | [[Escape velocity]]

| ~0.006 km/s

|-

! align="left" | [[Sidereal day|Rotation period]]

| [[synchronous rotation|synchronous]]

|-

! align="left" | [[Axial tilt]]

| zero

|-

! align="left" | [[Albedo]]

| 0.5

|-

! align="left" | Surface [[Temperature|temp.]]

|

{| cellspacing="0" cellpadding="2" border="0"

|-

! min !! mean !! max

|-

|

| ~78 K

|

|}

|-

! align="left" | [[celestial body's atmosphere|Atmosphere]]

| none

|}

'''Pan''' ''(pan,'' {{IPA2|ˈpæn}}, Greek ''Πάν)'' is the [[inner satellite|innermost moon]] of [[Saturn (planet)|Saturn]]. It was discovered by [[Mark R. Showalter]] in [[1990]] from analysis of old ''[[Voyager 2]]'' probe photos <ref>[http://cfa-www.harvard.edu/iauc/05000/05052.html#Item2 IAUC 5052]</ref>. Pan is within the [[Encke division]] in Saturn's [[A Ring]]; it acts as a [[shepherd satellite|shepherd]] and is responsible for keeping the Encke gap open. Its gravity produces wave patterns in the rings that indicated Pan's presence and led to the reexamination of Voyager photographs of its predicted ___location.<ref name="Showalter90">{{cite journal | author= M.R. Showalter| title= ''Visual Detection of 1981S13, the Encke Gap Moonlet''| journal= Bulletin of the American Astronomical Society| year= 1990| volume= 22| pages= 1031| url= http://adsabs.harvard.edu//full/seri/BAAS./0022//0001040.000.html}}</ref> Other undiscovered moons may exist within Saturn's rings.

'''Pan''' is the innermost named [[Moons of Saturn|moon of Saturn]].<ref name="Moons of Saturn">{{cite web |url=https://solarsystem.nasa.gov/planets/saturn/moons |archive-url=https://web.archive.org/web/20150907020115/http://solarsystem.nasa.gov/planets/saturn/moons |url-status=dead |archive-date=7 September 2015 |title=Saturn - Moons |work=NASA |access-date=5 October 2017}}</ref> It is approximately 35 kilometres across and 23&nbsp;km wide and orbits within the [[Encke Gap]] in Saturn's [[A Ring]]. Pan is a [[Shepherd moon|ring shepherd]] and is responsible for keeping the Encke Gap free of ring particles. It is sometimes described as having the appearance of a walnut, or {{Not a typo|[[raviolo]]}}.<ref name="Ravioli">{{cite web |title=Saturn's Tiny Moon Pan Looks Like a Ravioli |url=https://www.cnet.com/news/nasa-saturn-pan-cassini-ravioli-moon/ |access-date=8 January 2020 |work=CNET}}</ref>

The existence of such a moon in the [[Encke division]] was first predicted by [[Jeffrey N. Cuzzi]] and [[Jeffrey D. Scargle]] in [[1985]]. Then Showalter, ''et al.'' inferred its orbit and mass in [[1986]] by modeling its "wake", or gravitational disturbance. They arrived at a very precise prediction of 133,603 ± 10 km for the semi-major axis and a mass of 5&ndash;10{{e|&minus;12}} Saturn masses, and inferred that there was only a single moon within the Encke gap.<ref name="Showalter86">{{cite journal | author= M.R. Showalter et al| title= ''Satellite "wakes" and the orbit of the Encke Gap moonlet''| journal= Icarus| year= 1986| volume= 66| pages= 297| url= http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1986Icar...66..297S&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=444b66a47d24282}}</ref> The actual semi-major axis differs by 19 km and the actual mass is 8.6{{e|&minus;12}} of Saturn's.

Pan was discovered by [[Mark R. Showalter]] in 1990 from analysis of old ''Voyager 2'' probe photos and received the provisional designation '''{{nowrap|S/1981 S 13}}''' because the discovery images dated back to 1981.<ref name="iauc5052">[http://www.cbat.eps.harvard.edu/iauc/05000/05052.html IAUC 5052: ''Saturn''] July 16, 1990 (discovery)</ref>

The moon was later found within 1° of the predicted position. The search was undertaken by considering all [[Voyager 2]] images and using a computer calculation to predict whether the moon would be visible under sufficiently favorable conditions in each one. Every qualifying Voyager 2 image with resolution better than ~50 km/pixel shows Pan clearly. In all, it appears in eleven Voyager 2 images.<ref name="Showalter91">{{cite journal | author= M.R. Showalter| title= ''Visual detection of 1981S13, Saturn's eighteenth satellite, and its role in the Encke gap''| journal= Nature| year= 1991| volume= 351| pages= 709| url= http://www.nature.com/nature/journal/v351/n6329/abs/351709a0.html;jsessionid=96A389576D34C289DA630CFB55D40CB6}}</ref><ref name="Showalter90"/>

==Prediction and discovery==

The moon named after the god [[Pan (god)|Pan]], and is also designated '''Saturn&nbsp;XVIII'''.<ref name="Gazetteer">{{cite web

The existence of a moon in the Encke Gap was first predicted by Jeffrey N. Cuzzi and Jeffrey D. Scargle in 1985, based on wavy edges of the gap which indicated a gravitational disturbance.<ref>Cuzzi, J. N.; and Scargle, J. D.; [http://adsabs.harvard.edu//full/seri/ApJ../0292//0000276.000.html ''Wavy Edges Suggest Moonlet in Encke's Gap''], Astrophysical Journal, Vol. 292 (May 1, 1985), pp. 276–290</ref> In 1986, Showalter ''et al.'' inferred its orbit and mass by modeling its gravitational wake. They arrived at a precise prediction of 133,603 ± 10&nbsp;km for the semi-major axis and a mass of 5&ndash;10{{e|&minus;12}} Saturn masses, and inferred that there was only a single moon within the Encke gap.<ref name="Showalter1986">{{cite journal | author= Showalter, M. R. | display-authors= etal| title= Satellite "wakes" and the orbit of the Encke Gap moonlet| journal= Icarus| date= 1986| volume= 66 | issue= 2| pages= 297–323| bibcode= 1986Icar...66..297S | doi = 10.1016/0019-1035(86)90160-0| url= https://zenodo.org/record/1253894| doi-access= free}}</ref> The actual semi-major axis differs by 19&nbsp;km, and the actual mass is 8.6{{e|&minus;12}} of Saturn's.

| 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

| accessdate = 2006-08-07 }}</ref> After the discovery it received a temporary designation '''S/1981&nbsp;S&nbsp;13'''.

The moon was later found within 1° of the predicted position. The search was undertaken by considering all ''[[Voyager 2]]'' images and using a computer calculation to predict whether the moon would be visible under sufficiently favorable conditions in each one. Every qualifying Voyager 2 image with a resolution better than ~50&nbsp;km/pixel shows Pan clearly. In all, it appears in eleven ''Voyager 2'' images.<ref name="Showalter1990">{{cite journal | author=Showalter, M. R.| title= Visual Detection of 1981 S 13, the Encke Gap Moonlet| journal= Bulletin of the American Astronomical Society| date= 1990| volume= 22| pages= 1031| url= http://adsabs.harvard.edu//full/seri/BAAS./0022//0001040.000.html}}</ref><ref name="Showalter1991">{{cite journal | author= Showalter, M. R.| title= Visual detection of 1981 S 13, Saturn's eighteenth satellite, and its role in the Encke gap| journal= Nature| date= 1991| volume= 351 | issue= 6329| pages= 709–713| doi= 10.1038/351709a0|bibcode = 1991Natur.351..709S | s2cid= 4317496}}</ref>

There is also an [[asteroid]] called [[4450 Pan]].

== References Name==

The moon was named on 16 September 1991<ref>[http://www.cbat.eps.harvard.edu/iauc/05300/05347.html IAUC 5347: ''Satellites of Saturn and Neptune''] 1991 September 16 (naming the moon)</ref> after the mythological [[Greek mythology|Greek]] god named [[Pan (mythology)|Pan]], who was (among other things) the god of shepherds. This is a reference to Pan's role as a [[shepherd moon]]. It is also designated '''{{nowrap|Saturn XVIII}}'''.<ref name="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 = 2006-08-07 }}</ref>

<div class="references-small">

<references/>

:* [http://adsabs.harvard.edu//full/seri/ApJ../0292//0000276.000.html Cuzzi, J. N. & Scargle, J. D., "Wavy edges suggest moonlet in Encke's gap", ApJ '''292''' (1985) 276]

</div>

==Orbit==

== External links ==

The [[eccentricity (orbit)|eccentricity]] of Pan's orbit causes its distance from Saturn to vary by ~4&nbsp;km. Its [[inclination]], which would cause it to move up and down, is not distinguishable from zero with present data. The [[Encke Gap]], within which Pan orbits, is about 322&nbsp;km wide.<ref name="SaturnRingStats"/>

* [http://www.planetary.org/explore/topics/our_solar_system/saturn/pan.html The Planetary Society: Pan]

==Geography==

<div style="clear: both; margin-top: 2em; text-align: center;">''(Saturn) | '''Pan''' | [[Daphnis (moon)|Daphnis]] | ...''</div>

[[File:Pan (moon) edge-on.jpg|thumb|right|Pan, photographed by ''[[Cassini–Huygens|Cassini]]'' on March 7, 2017. The thin [[equatorial ridge]] is clearly visible.]]

''[[Cassini-Huygens|Cassini]]'' scientists have described Pan as "[[walnut]]-shaped"<ref>[http://photojournal.jpl.nasa.gov/catalog/PIA08320 "PIA08320: Cruising with Pan"], ''[[Planetary Photojournal]]''.</ref> owing to the [[equatorial ridge]], similar to that on [[Atlas (moon)|Atlas]], that is visible in images. The ridge is due to ring material that Pan has swept up from the Encke gap. It has been referred to by journalists as a space [[empanada]], a form of stuffed bread or pastry, as well as a [[ravioli]].<ref>{{cite news|last1=Chang|first1=Kenneth|title=Pan, Moon of Saturn, Looks Like a Cosmic Ravioli (or Maybe a Walnut)|url=https://www.nytimes.com/2017/03/10/science/nasa-cassini-saturn-moon-pan.html?_r=0|access-date=11 March 2017|work=The New York Times|date=10 March 2017}}</ref><ref name="Space empanada">{{Cite web |url=http://www.sciencemag.org/news/2017/03/space-empanada-frozen-ridge-around-saturn-s-moon-pan-collected-planet-s-rings |title= Stunning close-up of Saturn's moon, Pan, reveals a space empanada |last=Perkins |first=Sid |website=Science |date=2017-03-09}}</ref> A new study suggests that the bizarre shape of Pan could also be due to collisions between tiny [[Moonlet|moonlets]], thus causing them to merge and form Pan (known as the pyramidal regime formation scenario).<ref>{{Cite web|last=|first=|date=22 May 2018|title=Here's Why Saturn's Inner Moons Are Shaped Like Ravioli and Potatoes|url=https://www.space.com/40653-saturns-weird-moon-shapes-explained.html|access-date=8 February 2021|website=Space.com}}</ref>

==Pandean ringlet==

{{Saturn Full Footer}}

The Encke Gap contains a ringlet that is coincident with Pan's orbit, indicating that Pan maintains the particles in [[horseshoe orbit]]s.<ref>{{cite journal|last1=Hedman|first1=M.M.|last2=Burns|first2=J.A.|last3=Hamilton|first3=D.P.|last4=Showalter|first4=M.R.|title=Of horseshoes and heliotropes: Dynamics of dust in the Encke Gap|journal=Icarus|date=2013|volume=223|issue=1|pages=252–276|doi=10.1016/j.icarus.2012.11.036|arxiv=1211.4762|bibcode=2013Icar..223..252H|s2cid=974916}}</ref> A second ringlet is periodically disrupted by Pan, similarly to how the [[F Ring]] is disturbed by [[Prometheus (moon)|Prometheus]].<ref>{{cite journal|last1=Porco|first1=C.C.|last2=Baker|first2=E.|last3=Barbara|first3=John|last4=Beurle|first4=K.|last5=Brahic|first5=A.|last6=Burns|first6=J.A.|last7=Charnoz|first7=S.|last8=Cooper|first8=N.|last9=Dawson|first9=Douglas|last10=Delgenio|first10=Anthony|last11=Denk|first11=T.|last12=Dones|first12=Luke|last13=Dyudina|first13=Ulyana|last14=Evans|first14=M.W.|last15=Giese|first15=B.|last16=Grazier|first16=Kim|last17=Helfenstein|first17=Paul|last18=Ingersoll|first18=A.P.|last19=Jacobson|first19=R.A.|last20=West|first20=Robert|title=Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites|journal=Science|date=2005|volume=307|issue=5713|pages=1226–1236|doi=10.1126/science.1108056|pmid=15731439|bibcode=2005Sci...307.1226P|s2cid=1058405|url=https://resolver.caltech.edu/CaltechAUTHORS:20130123-162411418 }}</ref>

==Gallery==

[[Category:Saturn's moons]]

<gallery>

File:PIA06534 Encke Division.jpg|Closeup of the Encke Gap, showing the central ringlet that is coincident with Pan's orbit.

File:Pans highway 3-05-07.jpg|''Cassini'' image showing Pan orbiting in the Encke Gap.

File:Pan side view.jpg|Equatorial view of Pan from ''Cassini'', with the rings of Saturn surrounding the moon.

File:Pan Rev09.2x.jpg|Pan in the center of the image, occupying the Encke Gap in Saturn's rings. Its walnut-like shape is clearly visible.

File:PIA21436 - Pan, 3 versions.jpg|Stretched (4x) images, processed in various ways.

</gallery>

==See also==

*[[List of natural satellites]]

=== Notes ===

{{notelist}}

== References ==

{{reflist|30em|refs=

<ref name="SaturnRingStats">{{cite web |url=https://pds-rings.seti.org/saturn/saturn_tables.html |title=Vital Statistics for Saturn's Rings and Inner Satellites |publisher=NASA Planetary Data System |last= |first= |access-date= }}</ref>

<ref name="Thomas2020">{{cite journal

|first1 = P. C. |last1 = Thomas

|first2 = P. |last2 = Helfenstein

|title = The small inner satellites of Saturn: Shapes, structures and some implications

|journal = Icarus

|date = July 2020

|volume = 344

|id = 113355

|pages = 20

|doi = 10.1016/j.icarus.2019.06.016

|bibcode = 2020Icar..34413355T|s2cid = 197474587

}}</ref>

}}

== External links ==

{{Commons category|Pan (moon)}}

{{Spoken Wikipedia|Pan_(moon).ogg|date=2010-01-16}}

* [https://web.archive.org/web/20070609080459/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Pan Pan Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]

* [https://web.archive.org/web/20060927042138/http://www.planetary.org/explore/topics/our_solar_system/saturn/pan.html The Planetary Society: Pan]

{{Moons of Saturn|state=uncollapsed}}

[[als:Pan (Mond)]]

{{Saturn}}

[[bg:Пан (спътник)]]

{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}

[[ca:Pan (satèl·lit)]]

[[cs{{DEFAULTSORT:Pan (měsícMoon)]]}}

[[daCategory:PanMoons (måne)of Saturn]]

[[Category:Astronomical objects discovered in 1990|19900716]]

[[de:Pan (Mond)]]

[[Category:Moons with a prograde orbit]]

[[es:Pan (luna)]]

[[fr:Pan (lune)]]

[[hr:Pan (mjesec)]]

[[it:Pan (astronomia)]]

[[la:Pan (satelles)]]

[[nl:Pan (maan)]]

[[ja:パン (衛星)]]

[[nn:Saturnmånen Pan]]

[[pl:Pan (księżyc)]]

[[pt:Pã (satélite)]]

[[sk:Pan (mesiac)]]

[[sv:Pan (måne)]]

[[uk:Пан (супутник)]]

[[zh:土卫十八]]