Lagrange points and trojan moons

How a tiny moon can share an orbit with a big one.

Published 2026-10-23

Polydeuces travels around Saturn in the same orbit as Dione, which is about 1,123 km across.^[1][5]

Points of balance

Lagrange points are points of equilibrium for small objects under the gravity of two massive orbiting bodies.^[4]

L4 and L5

Two of these points lie 60° ahead of and behind the smaller body in its orbit. Objects near them are called trojans.

Dione’s companions

Helene is Dione’s leading co-orbital and Polydeuces the trailing one.^[2]

Not perfectly still

Polydeuces periodically drifts away from L5 — farther than any other of Saturn’s trojan moons.^[1]

Numbered citations link to the sources list on the Polydeuces overview page.