What is a moon?
A moon is a natural object that orbits a planet, dwarf planet or asteroid. Our solar system has hundreds of known moons, ranging from tiny rocks to worlds larger than the planet Mercury.
Moons are also called natural satellites. Earth has one large moon, while Mars has two small ones, Phobos and Deimos. The giant planets have many: Saturn has 274 confirmed moons, the most of any planet, and Jupiter has about 97. Mercury and Venus have none.
Moons form in different ways. Some formed from disks of material around young planets, like Jupiter's large moons. Some were captured by a planet's gravity, like many small, irregular moons. Earth's Moon probably formed from debris after a giant collision with the early Earth.
Amazing moons
Jupiter's moon Ganymede is the largest moon in the solar system, larger than Mercury. Io is the most volcanically active body known. Saturn's Titan has a thick atmosphere and methane lakes, and Enceladus sprays water from an ocean beneath its icy crust.
Did You Know?
Even some asteroids have moons. The asteroid Dinkinesh, visited by NASA's Lucy spacecraft in 2023, has a tiny contact-binary moon.