Top 10 largest moons in the Solar System

Diameter and mass answer different questions

Mean diameter describes the distance across a body using a representative size measurement. It does not say how much matter the body contains. Composition and density influence mass, so a diameter ranking should not be reused as a mass ranking. This distinction is especially useful for icy moons and rocky worlds. Ganymede and Titan are wider than Mercury, yet being wider does not turn either satellite into a planet: the orbital relationship and the physical measurement are separate properties.

The host planets in this answer set

Jupiter contributes Ganymede, Callisto, Io and Europa. Saturn contributes Titan and Rhea. Uranus contributes Titania and Oberon, while Triton orbits Neptune and our Moon orbits Earth. Grouping the answers by their host gives a useful way to understand the list after the game. It also exposes a common confusion: Titan and Titania are different bodies belonging to different planetary systems. Similar names are not interchangeable, even when both objects are large natural satellites.

What this size comparison leaves out

A large diameter does not measure habitability, surface temperature, atmospheric depth or scientific interest. Smaller moons can be important research targets for reasons unrelated to size. The outer boundary also needs a consistent convention: an atmosphere or a ring around a body should not be added to the solid-body diameter. NASA’s moon descriptions and satellite fact sheets are useful checks for names, host planets and measurements. The archive keeps its original 2024 ordering and does not claim to rank every newly identified small moon; new discoveries only matter here if their measured size would change the leading group.

Sources & further reading

• NASA: Solar System moons
• NASA: Jovian satellite fact sheet
• NASA: Saturnian satellite fact sheet

Explanation updated Thursday, October 1, 2026. The puzzle’s original data date is listed below.