Janus is an inner satellite of Saturn. It is also known as Saturn X. It is named after the mythological Janus.
Janus as imaged by Cassini on 7 April 2010: highest-resolution full-disk image to date
Epimetheus (lower left) and Janus (right) seen on 20 March 2006, two months after swapping orbits. The two moons appear close only because of foreshortening; in reality, Janus is about 40,000 km farther from Cassini than Epimetheus.
Janus as viewed by Voyager 2 (1981-08-25).
Janus and Prometheus lie above and below Saturn's rings (2006-04-29).
In astronomy, an inner moon or inner natural satellite is a natural satellite following a prograde, low-inclination orbit inwards of the large satellites of the parent planet. They are generally thought to have been formed in situ at the same time as the coalescence of the original planet. Neptune's moons are an exception, as they are likely reaggregates of the pieces of the original bodies, which were disrupted after the capture of the large moon Triton. Inner satellites are distinguished from other regular satellites by their proximity to the parent planet, their short orbital periods, their low mass, small size, and irregular shapes.
Jupiter's inner moons and rings
Diagram of Neptune's inner satellites.
