Pan (moon): Difference between revisions
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==Orbit== |
==Orbit== |
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The [[eccentricity (orbit)|eccentricity]] of Pan's orbit causes its distance from Saturn to vary by ~4 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 325 km wide. |
The [[eccentricity (orbit)|eccentricity]] of Pan's orbit causes its distance from Saturn to vary by ~4 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 325 km wide. |
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==Geography== |
==Geography== |
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''[[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. |
''[[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. |
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[[File:Pan (moon) edge-on.jpg|thumb|Pan, photographed by the [[Cassini–Huygens|Cassini]] probe on March 7, 2017. The thin [[equatorial ridge]] is clearly visible.]] |
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==Pandean ringlet== |
==Pandean ringlet== |
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[[File:PIA06534 Encke Division.jpg|thumb|240px|Closeup of the Encke Gap. The central ringlet is coincident with Pan's orbit.]] |
The Encke Gap contains a ringlet that is coincident with Pan's orbit, indicating that Pan maintains the particles in [[horseshoe orbit]]s. A second ringlet is periodically disrupted by Pan similarly to how the [[F Ring]] is disturbed by [[Prometheus (moon)|Prometheus]].[[File:PIA06534 Encke Division.jpg|thumb|240px|Closeup of the Encke Gap. The central ringlet is coincident with Pan's orbit.]] |
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The Encke Gap contains a ringlet that is coincident with Pan's orbit, indicating that Pan maintains the particles in [[horseshoe orbit]]s. A second ringlet is periodically disrupted by Pan similarly to how the [[F Ring]] is disturbed by [[Prometheus (moon)|Prometheus]]. |
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==Name== |
==Name== |
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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 [[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 |
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 [[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 |
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{{notelist}} |
{{notelist}} |
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;Citations |
;Citations |
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{{reflist|30em}} |
{{reflist|30em}} |
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== External links == |
== External links == |
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{{Commons category|Pan (moon)}} |
{{Commons category|Pan (moon)}} |
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{{Spoken Wikipedia|Pan_(moon).ogg|2010-01-16}} |
{{Spoken Wikipedia|Pan_(moon).ogg|2010-01-16}} |
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* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Pan Pan Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration] |
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Pan Pan Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration] |
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Revision as of 17:39, 9 March 2017
 View of Pan by Cassini in 2017.[a] | |
| Discovery | |
|---|---|
| Discovered by | M. R. Showalter |
| Discovery date | July 16, 1990 |
| Designations | |
| Adjectives | Pan |
| Orbital characteristics[1] | |
| 133584.0±0.1 km | |
| Eccentricity | 0.0000144±0.0000054 |
| 0.575050718 d (13.801217 h) | |
| Inclination | 0.0001°±0.0004° |
| Satellite of | Saturn |
| Physical characteristics | |
| Dimensions | 34.4 × 31.4 × 20.8 km |
| 14.1±1.3 km[2] | |
| Mass | (4.95±0.75)×1015 kg[2] |
Mean density | 0.42±0.15 g/cm³[2] |
| 0.0001–0.0018 m/s2 | |
| ≈ 0.006 km/s | |
| synchronous | |
| zero | |
| Albedo | 0.5 |
| Temperature | ≈ 78 K |
Pan (/ˈpæn/ PAN, Greek: Πάν) is the second-innermost moon of Saturn. It is a walnut-shaped small moon about 35 kilometres across and 23 km high that orbits within the Encke Gap in Saturn's A Ring. Pan is a ring shepherd and is responsible for keeping the Encke Gap free of ring particles.
It was discovered by Mark R. Showalter in 1990 from analysis of old Voyager 2 probe photos and received the provisional designation S/1981 S 13 because the discovery images dated back to 1981.[3]
Prediction
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.[4] In 1986 Showalter et al. inferred its orbit and mass by modeling its gravitational wake. They arrived at a very precise prediction of 133,603 ± 10 km for the semi-major axis and a mass of 5–10×10−12 Saturn masses, and inferred that there was only a single moon within the Encke gap.[5] The actual semi-major axis differs by 19 km and the actual mass is 8.6×10−12 of Saturn's.
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.[6][7]
Orbit
The eccentricity of Pan's orbit causes its distance from Saturn to vary by ~4 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 325 km wide.
Geography
Cassini scientists have described Pan as "walnut-shaped"[8] owing to the equatorial ridge, similar to that on Atlas, that is visible in images. The ridge is due to ring material that Pan has swept up from the Encke gap.
_edge-on.jpg)
Pandean ringlet
The Encke Gap contains a ringlet that is coincident with Pan's orbit, indicating that Pan maintains the particles in horseshoe orbits. A second ringlet is periodically disrupted by Pan similarly to how the F Ring is disturbed by Prometheus.
Name
The moon was named on 16 September 1991,[9] after the mythological 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 Saturn XVIII.[10]
References
- Notes
- ^ This photo of Pan was acquired by the 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.
- Citations
- ^ Jacobson, R. A.; et al. (2008). "Revised orbits of Saturn's small inner satellites". Astronomical Journal. 135 (1): 261–263. Bibcode:2008AJ....135..261J. doi:10.1088/0004-6256/135/1/261.
- ^ a b c Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus. 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025.
{{cite journal}}: Invalid|ref=harv(help) - ^ IAUC 5052: Saturn July 16, 1990 (discovery)
- ^ Cuzzi, J. N.; and Scargle, J. D.; Wavy Edges Suggest Moonlet in Encke's Gap, Astrophysical Journal, Vol. 292 (May 1, 1985), pp. 276–290
- ^ Showalter, M. R.; et al. (1986). "Satellite "wakes" and the orbit of the Encke Gap moonlet". Icarus. 66 (2): 297. Bibcode:1986Icar...66..297S. doi:10.1016/0019-1035(86)90160-0.
- ^ Showalter, M. R. (1990). "Visual Detection of 1981 S 13, the Encke Gap Moonlet". Bulletin of the American Astronomical Society. 22: 1031.
- ^ Showalter, M. R. (1991). "Visual detection of 1981 S 13, Saturn's eighteenth satellite, and its role in the Encke gap". Nature. 351 (6329): 709. Bibcode:1991Natur.351..709S. doi:10.1038/351709a0.
- ^ "PIA08320: Cruising with Pan", Planetary Photojournal.
- ^ IAUC 5347: Satellites of Saturn and Neptune 1991 September 16 (naming the moon)
- ^ "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. 21 July 2006. Retrieved 7 August 2006.
External links
