Atlas . Saturn XV - 1980S28 . Atlas, the second of Saturn's known satellites, orbits near the outer edge of the A-ring and is about 40 by 20 kilometers (25 by 15 miles) in size. It is probably a shepherd satellite for Saturn's A-ring. Atlas was discovered by R. Terrile in 1980 from photographs taken by Voyager during its encounter with Saturn. Atlas Statistics . ... Mean density (gm/cm^3) . ... Rotational period (days) . Orbital period (days) . ... Credit: Calvin J. Hamilton) . ...