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, that was seen 5 hours earlier just on the farther edge of the F ring. The announcement was made on September 9, 2004.
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.
An interpretation where S3 and S4 are or were a single object on a F-ring crossing orbit is also possible. 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, would be 3−5 km in diameter based on brightness.