Why does the Solar System have so many moons around the giant planets?
Quick Answer
The giant planets formed with large disks of material around them and had enough gravity to capture many objects. Their strong gravity also helped keep those moons in place.
The Full Story
Jupiter, Saturn, Uranus and Neptune each formed in regions where there was plenty of material, and their strong gravity let them gather and retain many moons. Some moons formed from disks of debris around the young planets, while others were likely captured later. The giant planets' large Hill spheres give them a wide gravitational reach, making it easier to hold onto satellites. Smaller inner planets have fewer moons because their gravity is weaker and they had less material available. The contrast between the giant planets and the terrestrial planets is one of the clearest patterns in the Solar System.
Key Facts
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