The largest moon in the solar system is

Ganymede is the largest moon in the solar system (larger than the planet Mercury), and is the only moon known to have its own internally generated magnetic field.

Titan is the second largest moon in our solar system. Only Jupiter's moon Ganymede is larger, by just 2 percent. Titan is bigger than Earth's moon, and larger than even the planet Mercury.

Ganymede is one of the four Galilean moons discovered by Galileo in 1610. It is the largest of Jupiter's seventy-nine moons and the largest moon in the solar system. With a diameter of 5,148 kilometers (3,273 miles), Ganymede is slightly larger than Mercury but almost 2.4 times smaller than Earth.