Telesto is a trojan moon of Tethys and therefore occupies the same orbit as Tethys and its other trojan, Calypso. One might expect the gravity of the larger Tethys to have a sweeping effect, clearing the orbit of objects that might create impact craters. Note that Calypso also appears smooth, though we do not have as good a picture as we have for Telesto.

Cool; new lesson in Lagrange points!