One of Jupiter's moons is as big as the planet mercury if the moon is so big why is it a moon and not a planet?

Answer 1

it doesn't orbit the sun. it only orbits jupiter.

Answer 2

Jupiter's moon Ganymede is as big as Mercury but is classified as a moon because it orbits Jupiter rather than orbiting the sun directly. Planets are celestial bodies that orbit the sun directly, while moons orbit planets. Ganymede's orbit around Jupiter classifies it as a moon rather than a planet.