Pan is the innermost named
moon of Saturn.
It is approximately 35 kilometres across and 23 km wide and 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 is sometimes described as having the appearance of a walnut, or
ravioli.
Pan was discovered by
Mark R. Showalter in 1990 from analysis of old ''Voyager 2'' probe photos and received the provisional designation because the discovery images dated back to 1981.
[IAUC 5052: ''Saturn''](_blank)
July 16, 1990 (discovery)
Prediction and discovery
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. 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 km for the semi-major axis and a mass of 5–10 Saturn masses, and inferred that there was only a single moon within the Encke gap.
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 a resolution better than ~50 km/pixel shows Pan clearly. In all, it appears in eleven ''Voyager 2'' images.
Name
The moon was named on 16 September 1991 after the mythological
Greek god named
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 .
Orbit
The
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
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 322 km wide.
Geography
''
Cassini'' scientists have described Pan as "
walnut-shaped" owing to the
equatorial ridge, similar to that on
Atlas
An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets.
Atlases have traditio ...
, 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.
A new study suggests that the bizarre shape of Pan could also be due to collisions between tiny
moonlets, thus causing them to merge and form Pan (known as the pyramidal regime formation scenario).
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.
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.
See also
*
List of natural satellites
Notes
References
External links
Pan Profileb
NASA's Solar System Exploration
{{DEFAULTSORT:Pan (Moon)
Moons of Saturn
19900716
Moons with a prograde orbit