S/2004 S 4

S/2004 S 4 is the designation of an object that astronomers do not know for sure if it exists seen orbiting Saturn within the closer part of the F ring on 21 June, 2004. It was seen while J. N. Spitale was trying to confirm the orbit of another object, S/2004 S 3 that was seen 5 hours earlier just on the farther edge of the F ring.[1] The announcement was made on September 9, 2004.[3]

S/2004 S 4
Discovery
Discovered by Joseph Spitale / Cassini Imaging Science Team Archived 2011-05-20 at the Wayback Machine.[1]
Discovered on 21 June, 2004
Orbital characteristics
Semimajor axis ~140,100 km.[2]
Eccentricity unknown, small
Orbital period ~0.618 d [2]
Inclination unknown, small
Is a satellite of Saturn
Physical characteristics
Mean diameter 3–5 km
Rotation period probably synchronous
Axial tilt unknown
Albedo unknown
Atmosphere none

Even though astronomers tried to find it again, it has not been reliably seen since. Notably, an imaging sequence covering an entire orbital period at 4 km resolution taken on 15 November, 2004 failed to find the object. This suggests that it was a clump of material that had disappeared by that time.[4]

An interpretation where S3 and S4 are or were a single object on a F-ring crossing orbit is also possible.[3] Such an object might also be orbiting at a bit different inclination to the F ring, thereby not actually passing through the ring material even though it was being seen both radially inward and outward of it.

If a solid object after all, S/2004 S 4 would be 3−5 km in diameter based on brightness.

References
  1. Martinez, C.; Ormrod, G.; and Finn, H.; Cassini-Huygens Press Releases: Cassini Discovers Ring and One, Possibly Two, Objects at Saturn Archived 2004-10-16 at the Wayback Machine September 9, 2004
  2. PGJ Astronomie webpage (Gilbert Javaux) Note that the F ring is centered at ~140,180 km
  3. IAUC 8401: S/2004 S 3, S/2004 S 4, and R/2004 S 1 2004 September 9 (discovery)
  4. Spitale, J. N.; et al. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal. 132 (2): 692–710. Bibcode:2006AJ....132..692S. doi:10.1086/505206. S2CID 26603974.
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