Saturn's Possible New Moons

There have been many observations that seem to indicate additional small moons close to Saturn. None have been confirmed, however. Most if not all will probably turn out to have been observational flukes.

Facts

• The image above shows Epimetheus on the left and S/1995 S 3 on the right.

• Here are the provisional designations and orbital radii of some of the reported but as yet unconfirmed and unnamed moons of Saturn:
  

                         Distance
            Designation    (km)
            -----------  --------
            S/1981 S 7
            S/1981 S 10
            S/1981 S 11
            S/1981 S 14   200000?
            
            S/1981 S 15   174000
            S/1981 S 16   220000
            S/1981 S 17   231000
            S/1981 S 18   185000
            S/1981 S 19   186000
            
            S/1995 S 1    137450
            S/1995 S 2    139700
            S/1995 S 3    141050
            S/1995 S 4    146450
  
            S/1995 S 5    140060
            S/1995 S 6    139910
            S/1995 S 7    139440
  

  The first two groups are derived from analysis of Voyager 2 data reported in IAUC 6162; the third group is from HST observations during the May 1995 ring plane crossing by Amanda S. Bosh and graduate student Andrew S. Rivkin and reported in IAUC 6192; the fourth group is from HST observations by P. D. Nicholson et al during the August 1995 ring plane crossing as reported in IAUC 6243.

• Several others have also been reported (IAUC 3651, 3656 and 3660) but IAUC 6162 indicates that the new satellites previously reported should be reduced to the four in the first group above.

• It is possible that some of these are actually the same as some of the known satellites (e.g. S/1995 S 1 may be Atlas and S/1995 S 2 may be Prometheus or S/1995 S 1 may be Pan and S/1995 S 2 one of the others); better orbital determinations will be needed to sort it out. IAUC 6243 confirms the probable identification of S/1995 S 2.

• The orbit of S/1995 S 7 is "indistinguishable" from that of S/1995 S 2 (= Prometheus) but S/1995 S 7 trails behind by 15 degrees.

• S/1995 S 3 orbits just outside the F ring and is apparently a shepherd moon. There are two other F ring shepherds ( Prometheus and Pandora), the presence of a third may account for the F ring's braided appearance.

• IAUC 6243 indicates that S/1995 S 5 and S/1995 S 6 may be just clumps or arcs of ring material rather than true satellites.

• These objects, if they are real, are all very small, just a few tens of kilometers in diameter.

• Ring plane crossings are particularly favorable for seeing small moons since the normally bright glare of the rings is absent. 13 of Saturn's 18 known moons were discovered during ring plane crossings.

• It now appears that none of these are real. They are most likely just short-lived clumps of material.

• All doubt should be laid to rest with the arrival at Saturn of the Cassini spacecraft in 2004.

Pictures

1. (above) S/1995 S 3 and Epimetheus 47k jpg; 180k gif (caption)
2. Pandora and S/1995 S 6 from ESO 61k gif (caption)
3. HST view of the motions of Saturn's inner satellites 307k gif (caption)

More about new Saturnian moons

• from LANL
• Saturn Ring Plane Crossing Home Page
• Ring plane crossing info from STScI
• press release about S/1995 S 3
• IAU Circular 6162 (Voyager)
• IAU Circular 6192 (HST)
• note from IAU Circular 6196
• IAU Circular 6243 (HST)