Pan (moon)
From Wikipedia, the free encyclopedia
 Pan amid the rings of Saturn. The 'side' view gives Pan the appearance of being embedded in the rings, although it actually travels in the empty Encke Division. |
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| Discovery | |
|---|---|
| Discovered by: | M. R. Showalter |
| Discovery date: | July 16, 1990 |
| Orbital characteristics [1] | |
| Semi-major axis: | 133,584.0±0.1 km |
| Eccentricity: | 0.000035±0.000007 |
| Orbital period: | 0.575050718 d |
| Inclination: | 0.0010±0.0006° |
| Satellite of: | Saturn |
| Physical characteristics | |
| Dimensions: | 35 × 35 × 23 km [2] |
| Mean radius: | 15 ± 2 km [2] |
| Mass: | 4.9 ± 0.7 ×1015 kg [2] |
| Mean density: | 0.36 ± 0.16 g/cm³ |
| Equatorial surface gravity: | 0.001 m/s2 |
| Escape velocity: | ~0.006 km/s |
| Rotation period: | synchronous |
| Axial tilt: | zero |
| Albedo: | 0.5 |
| Temperature: | ~78 K |
Pan (pan, IPA: [ˈpæn], Greek Πάν) is the innermost moon of Saturn. It was discovered by Mark R. Showalter in 1990 from analysis of old Voyager 2 probe photos [3]. Pan is about 20 – 30 kilometers across and orbits within the Encke division in Saturn's A Ring; it acts as a 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.[4] Other undiscovered moons may exist within Saturn's rings.
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 5–10×10−12 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][4]
The moon is named after the god Pan, and is also designated Saturn XVIII.[7] After the discovery it received a temporary designation S/1981 S 13.
There is also an asteroid called 4450 Pan.
[edit] Gallery of Pan images
 Pan and the rings of Saturn, as photographed by the Cassini spacecraft on April 29, 2006. This image was taken appox. 130,000 miles away from a 'side' view of the rings, giving Pan the appearance of being in the ring's debris field, although in actuality it occupies the empty Encke Division between the rings. The object in the lower right of the photo is a bright background star. |
 This image was captured by the Cassini spacecraft's narrow-angle camera on January 19th, 2007 at an approximate distance of 1 million kilometers (600,000 miles) from Pan. The view is approx 35 degrees above the ringplane and shows Pan speeding along through the Encke Gap. |
[edit] References
- ^ J.N. Spitale et al (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692.
- ^ a b c C.C. Porco et al. (2006). "Physical characteristics and possible accretionary origins for Saturn's small satellites". Bulletin of the American Astronomical Society 37: 768.
- ^ IAUC 5052
- ^ a b M.R. Showalter (1990). "Visual Detection of 1981S13, the Encke Gap Moonlet". Bulletin of the American Astronomical Society 22: 1031.
- ^ M.R. Showalter et al (1986). "Satellite "wakes" and the orbit of the Encke Gap moonlet". Icarus 66: 297.
- ^ M.R. Showalter (1991). "Visual detection of 1981S13, Saturn's eighteenth satellite, and its role in the Encke gap". Nature 351: 709.
- ^ Planet and Satellite Names and Discoverers. Gazetteer of Planetary Nomenclature. USGS Astrogeology (July 21, 2006). Retrieved on August 7, 2006.
[edit] External links
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Generally listed in increasing distance from Saturn
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| Ring shepherds | Pan · Daphnis · Atlas · Prometheus · S/2004 S 6? · S/2004 S 4? · S/2004 S 3? · Pandora |
| Co-orbitals | Epimetheus · Janus |
| Inner large and Trojan | Mimas · Methone · Pallene · Enceladus · Tethys (trojans Telesto, Calypso) · Dione (trojans Helene, Polydeuces) |
| Outer large | Rhea · Titan · Hyperion · Iapetus |
| Inuit group | Kiviuq · Ijiraq · Paaliaq · Siarnaq |
| Norse group | Phoebe · Skathi · Skoll · S/2004 S 13 · S/2006 S 4 · Hyrokkin · Mundilfari · S/2006 S 6 · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot |
| Gallic group | Albiorix · Bebhionn · Erriapo · Tarvos |
