Dione ( "dy OH nee" ) is the twelfth of Saturn 's known satellites: orbit : 377,400 km from Saturn diameter : 1120 km mass : 1.05e21 kg . ... Both rotate synchronously and have dissimilar leading and trailing hemispheres. ... Helene orbits in Dione's leading Lagrange point. more images . ... Helene is in Dione's leading Lagrange point and hence was sometimes referred to as "Dione B". from LANL . How did Helene come to be in Dione's Lagrange point? ... Saturn .. ... Dione / Helene .. ...