An Explanation of Why Some Planets Have More Moons Than Others Do

My name's Eric Loberg, with the Taylor Planetarium at the Museum of the Rockies. And I was going to explain why some planets have more moons than others do. Some of it is just a feature of where the planets are located at and how they form. Most planets form when the little chunks of rock in the solar system started to come together and form larger and larger planets. If these planets were close to asteroid belts, you may get more moons because those asteroids will be captured by the planets. So, planets like Mars who has two moons, or Pluto who has five, often those are near asteroid belts and they have few more moons than some of the smaller ones. Small planets like Mercury or even Venus and Earth were closer to the Sun. The Sun absorbed most of that material that was leftover. And so, we don't have very many moons. The Earth's moon was probably a Mars size object that came from outside our solar system. Some of these objects came in, in an early bombardment period and smashed into the Earth. And that's what formed our moon. Why some planets have many moons is basically because of their size. The planets in our solar system that have more moons are the large planets, Jupiter, Saturn, Uranus and Neptune. They're so big that they can collect a lot of moon. If comets swing by them, they can sometimes absorb comets, they can grab asteroids. And there's a lot more material as it starts to condense into that big planet. There is more left behind that swirled around the planet and it left more moons. We can look at the number of moons in the solar system. Mercury has zero moons and is close to the Sun, Venus has zero moons, also close to the Sun. Earth has our one, which was probably a large impact that came from farther out. And Mars has two moons. All of these planets were very close to that great, big Sun and the Sun absorbed most of those objects. Mars probably has two because there's a big asteroid belt between Mars and Jupiter. Jupiter has 50, the largest planet, Saturn, second largest planet, has 53. Uranus also very large, 27, Neptune, farthest away has 14. And then, there's another kind of rocky asteroid belt called the Kuiper belt, Pluto out there has five. Just because it was near those little rocky leftovers, so it could grab some of them. so, why do some planets have more moons than others? Mostly because of their size, the larger planets have more moons. I'm Eric Loberg, with the Museum of the Rockies, Taylor Planetarium.