How big is our moon compared to the moons of other planets in our solar system and elsewhere?
There are four other moons in the Solar System larger than ours: In order of size, they are Ganymede, Titan, Callisto and Io. Titan orbits Saturn, while the other three all orbit Jupiter. Europa, the fourth large moon of Jupiter, is slightly smaller than our moon, and the next largest moon after that is Triton, which orbits Neptune and is the smallest of the seven large moons in the Solar System. As for moons outside the Solar System, we really have no idea because we haven’t see any yet. However, we do know that there exist planets in a wide variety of sizes, including many that are significantly more massive even than Jupiter. It is entirely possible for such planets to have moons that are not only larger than Ganymede, but quite possibly larger even than the Earth. In other words, it would be conceivable for the Earth itself to be a gas giant moon if it were positioned in the right place.
