Planetary orbiters, or moons, are celestial bodies that orbit around planets. They are typically much smaller than the planet they orbit and can range in size from tiny asteroids to large moons like Jupiter's Ganymede. Moons are often composed of rock, ice, or a combination of both. They can also have atmospheres, although these are usually much thinner than those of planets. Moons can be found orbiting all of the planets in our Solar System, with some planets having multiple moons.