Saturn's largest moon is called TITAN, which has a diameter of 5150 km and is the second-largest moon in the Solar System. It is the only moon known to have a dense atmosphere and is the only object in space other than Earth where clear evidence of stable bodies of surface liquid has been found. TITAN is composed of roughly 50% water ice and 50% rocky material. It is the only moon in the Solar System known to have a substantial atmosphere, which is composed primarily of nitrogen.