This photo illustration shows selected moons of our solar system at their correct relative sizes to each other and to Earth.

Moons in Brief
Many of the moons of our solar system are as intriguing as the planets. Earth's Moon holds many clues to the formation of our home world and rest of the solar system and offers a potential starting point for humanity to extend its reach deeper into space. Jupiter's Europa and Ganymede harbor signs of possible subsurface oceans. Saturn's large moon Titan is the only moon in the solar system known to have clouds, a mysterious, thick, planet-like atmosphere and surface lakes.
the planetary moons probably formed from the discs of gas and dust circulating around planets in the early solar system.

Astronomers have found at least 146 moons orbiting planets in our solar system. This number does not include the six moons of the dwarf planets, nor does this tally include the tiny satellites that orbit some asteroids and other celestial objects. Another 21 moons are awaiting official confirmation of their discovery.

Featured Mission: Europa Jupiter System Mission
This mission calls for two robotic orbiters working together to determine whether the Jovian system harbors habitable worlds. The spacecraft will focus much of their attention on Europa and Ganymede, both of which many harbor oceans under their icy crusts.

Read More About Moons of Our Solar System