Significance
  ============
    Pan is the innermost of Saturn's known moons.  It orbits near the
    middle of the 320-km-wide Encke Gap in Saturn's A Ring, and is
    believed to 'shepherd' it open.
 
 
  History
  =======
    The existence of a moon embedded in Saturn's Encke Gap was first
    proposed by [CUZZI&SCARGLE1985].  They noticed that the gap has
    wavy edges in the finest-resolution Voyager images, and showed how
    these wavy edges could be the results of gravitational
    perturbations from one or more nearby moons.  Shortly thereafter,
    [SHOWALTERETAL1986] were studying other wavelike patterns in the
    occultation data from the Voyager photopolarimeter and radio
    science experiments.  They were able to explain these patterns as
    the gravitational 'wake' of the same moon.  In the process, they
    were able to show that only a single major moon could be present
    in the gap, and derived reliable estimates of its orbit and mass.
    Finally, [SHOWALTER1991] used this orbit to perform a systematic
    search through the Voyager images and determine exactly which ones
    should have captured the moon; Pan was visible in the first image
    examined.
 
    Pan was named after the Greek god of shepherds, because it is
    believed to keep the Encke Gap open via the process widely known
    as 'shepherding.'
 
 
  Description
  ===========
    Pan was never resolved spatially in any images.  Its mass is
    estimated from its gravitational effects on the ring.  Assuming a
    water ice composition, the implied radius is 10 km.  Pan's
    disk-integrated brightness is also consistent with this radius,
    assuming a plausible surface albedo of 0.4-0.6.  Nothing is known
    about its shape or rotation period, although it is expected to be
    in sychronous rotation.
 
 
  Pan Quick-Look Statistics
  =========================
    Discovery:                           July 1990, by Mark Showalter
    Diameter (km):                       ~20
    Mass (kg):                           3e15 - 6e15
    Mass (Earth = 1):                    5e-10 - 1e-9
    Surface Gravity (Earth = 1):         UNK
    Mean Distance from Saturn (km):      133583.
    Mean Distance From Saturn (Rs):      2.2142
    Mean Distance from Sun (AU):         9.5388
    Orbital period (days):               0.575039
    Rotational period  (days):           0.575039
    Density (gm/cm**3)                   ~1
    Orbit Eccentricity:                  0.
    Orbit Inclination (degrees):         0.?
    Orbit Speed (km/sec):                16.8935
    Escape velocity (km/sec):            UNK
    Visual Albedo:                       0.4 - 0.6
    Surface Composition:                 Water ice