This image shows the moon Daphnis in the Keeler gap in Saturn's A ring. The moon's gravity causes the wave shapes in the rings. By NASA/JPL/Space Science Institute - http://www.esa.int/SPECIALS/Cassini-Huygens/SEM1XQ5TI8E_1.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17953334