Why does earth only have one moon, while other planets have many? Jupiter alone has nearly 40 moons!
Astronomers think that our moon was created billions of years ago when something really large collided with Earth, knocking rocks and debris into orbit. The orbiting stuff eventually came together to form the moon. When it comes to larger planets like Jupiter, it's possible that when the planet was still young its atmosphere stretched out far into surrounding space. The gas could have trapped passing objects and drawn them into Jupiter's orbit, creating small, irregular moons.
Earth might only have one moon, but it's a pretty good one, as moons go. First, it's a very large moon relative to the size of our planet. Also, it's close enough to have a significant effect on ocean tides and climate. Plus, our moon makes for some pretty spectacular nighttime sky gazing.