why do some planets have more moons than others
Yep, you are partially correct that the mass of a planet roughly correlates with the number of moons. However, there are way more factors that go into how many moons a planet will have. Let s get the mass part out of the way first. Every object has a
which is the volume of space in which that object is the dominant attractor. This means that Jupiter has a much bigger attraction space than Earth, so that alone tells us it will have more moons, and you can see this pattern roughly holds true. The second thing we can consider is the area of the solar system. Mercury and Venus, in addition to having relatively low masses (especially Mercury), have tighter orbits with the Sun, meaning they orbit in a smaller circle, giving them less of a chance to pick up a moon. Plus, the Sun is so massive that if anything approaches closely to it, it will be at high speeds.
Next, not all moons are created equally. This is a very important consideration. Mars has two moons, more than Earth, but they are both very tiny asteroids that were most likely captured from the asteroid belt. Our Moon in comparison. In contrast to capturing the Moon, one of the leading speculations is that our Moon is the result of a big collision early on in the solar system s history, and all of the ejected material from Earth and the other body coalesced to form the Moon. In comparison to the other planet-moon systems, the Earth and Moon are the closest in size to each other. This is also relevant to Jupiter. Of its, only FOUR of them are of any note; the rest are thousands of times less massive and most are captured asteroids, like with Mars.
Saturn has about seven moons of note, and Titan completely dominates the total mass of all the moons. It is interesting because we can see the ring moons within Saturn s rings, potentially supporting the Moon formation hypothesis. Uranus has five moons of note, and Neptune only has Triton. These gas giants have a much better chance of attracting passing asteroids because of their Hill Sphere as well as their perimeter/area of orbit, than the inner planets do. Pluto is kind of weird. It is an example of self-contained. The objects in the Pluto system orbit a common center of mass, and they are all very close. They are also incredibly tiny, with three of them less than 40 miles across. Pluto lies within the, so it has lots of chances of picking stuff up, even with a tiny Hill Sphere.
It and Charon managed to pick up three tiny objects, which again, is very different than how our Moon came to be! Hope all of that helps! Moons are formed out of debris that used to orbit a planet or still does, in the case of planets with rings like Jupiter or Saturn. A recent study found that moons are made by clumps of matter moving outwards from the rings and merging together. This is apparently still happening for Saturn, although very slowly. So why do rings of debris form? Either they re captured by the planet from debris in the solar system, or formed when something big collides with the planet (which is how the Moon was formed around Earth). Venus doesn t have a moon, which means that it probably didn t collide with anything big enough to make one.
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