Lagrangian point
Calypso is co-orbital with the moon Tethys, and resides in Tethys' trailing Lagrangian point (), 60 degrees behind Tethys. This relationship was first identified by Seidelmann "et al." in 1981. The moon Telesto resides in the other (leading) Lagrangian point of Tethys, 60 degrees in the other direction from Tethys. Calypso and Telesto have been termed "Tethys trojans", by analogy to the trojan asteroids, and are half of the four presently known trojan moons.