... A Great White Spot on Rhea . ... Why caused this great white spot on the surface of Saturn's moon Rhea? ... Cassini's flyby of Rhea in April imaged in the spot in great detail. ... To help find out, the robot Cassini spacecraft now orbiting Saturn broadcast radio waves of three different wavelengths right through the rings to Earth earlier this month. ... What causes small waves in Saturn's rings? Observations of rings bordering the Keeler gap in Saturn's rings showed unusual waves. ... April . ...