Jupiter
Jupiter has 95 known moons, as of February 23, 2023. The four largest were seen by Galileo with his primitive telescope and nine more can be seen with modern telescopes. Three moons were identified by the Voyager spacecraft. All other moons were first seen on Earth, using modern telescopes and advanced photography methods. The smallest moon (S/2003 J 12) is only one kilometre across. The largest, Ganymede, has a diameter of 5,262 kilometres. It is bigger than the planet Mercury. The other three Galilean moons are Io, Europa and Callisto. Due to the way they orbit Jupiter, gravity affects three of these moons greatly. The friction caused by the gravity of Europa and Ganymede pulling on Io makes it the most volcanic object in the Solar System. It has over 400 volcanoes, more than three times as many as Earth.