Discovered by Audouin Dollfus Date of Discovery 1966 Distance from Saturn 151,472 km Radius 97.0 × 95.0 × 77.0 km Mass 1.92 × 10^21 g Orbital Eccentricity 0.007 Orbital Inclination 0.14° Orbital Period 0.6945 day Rotational Period Synchronous Density (gm/cm3) ???
Janus and Epimetheus may have been part of the same body at one time. They share nearly the same orbit, but unlike co-orbital moons like Rhea and Diomed, their orbit is not stable. In fact, about once every four years they switch places, one being slightly higher than the other. Janus is heavily cratered so if it and Epimetheus were truly once a single entity, the event causing the split must have happened early in its history, billions of years ago. It is irregularly shaped, but unlike Epimetheus, it has no significant ridges, fissures, or grooves.
Sources: NASA.gov space.com