PAN (MOON)

:''For the moon of Jupiter known by this name 1955-1975, see Carme (moon).''


'Pan' ''(pan,'' , 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 and received the provisional designation 'S/1981 S 13' because the discovery images dated back to 1981.^[3] Pan is about 20 – 30 kilometres 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.^[5] 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 5–10Saturn masses, and inferred that there was only a single moon within the Encke gap.^[6] The actual semi-major axis differs by 19 km and the actual mass is 8.6 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.^[7]
The moon was named after the god Pan on 16 September 1991,^[8] and is also designated 'Saturn XVIII'.^[9]
There is also an asteroid called 4450 Pan.

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References

1. ''The orbits of Saturn's small satellites derived from combined historic and ''Cassini'' imaging observations'', Spitale, J. N.; ''et al.'', , , The Astronomical Journal, 2006
2. ''Physical Characteristics and Possible Accretionary Origins for Saturn's Small Satellites'', Porco, C. C.; ''et al.'', , , Bulletin of the American Astronomical Society, 2006
3. IAUC 5052: ''Saturn'' 1990 July 16 (discovery)
4. ''Visual Detection of 1981 S 13, the Encke Gap Moonlet'', Showalter, M. R., , , Bulletin of the American Astronomical Society, 1990
5. 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
6. ''Satellite "wakes" and the orbit of the Encke Gap moonlet'', Showalter, M. R.; ''et al.'', , , Icarus, 1986
7. ''Visual detection of 1981 S 13, Saturn's eighteenth satellite, and its role in the Encke gap'', Showalter, M. R., , , Nature, 1991
8. IAUC 5347: ''Satellites of Saturn and Neptune'' 1991 September 16 (naming the moon)
9. Planet and Satellite Names and Discoverers

External links

★ Pan Profile by NASA's Solar System Exploration

★ The Planetary Society: Pan
''(Saturn) | 'Pan' | Daphnis | ...''