Epimetheus

Cassini encounters Titan (and sees a region not yet mapped at high resolution) sometime today, but there won't be any pictures until tomorrow. Meanwhile there's some interesting stuff from the past day or so in the raw images archive: a respectable flyby of Rhea, and the best pictures ever by far of Epimetheus. Epimetheus and its co-orbital friend Janus are particularly strange: they have slightly different orbits separated by less than the moons' diameters. Every few years they approach one another, but instead of colliding, they do a gravitational energy swap in which they switch orbits.

There was a lot of confusion over Janus and Epimetheus early on because astronomers assumed there was one object there and got inconsistent results for its orbit from the few observations available. Pioneer 11, the first spacecraft ever to approach Saturn, nearly hit one of them in 1979, though there's enough uncertainty in their orbits that which one it was is unclear.