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Why does Earth have a moon and not Venus or Mars? And why Saturn has rings and not the inner planets?
Question Date: 2015-05-22
Answer 1:

You are correct that Venus does not have a moon, but Mars actually has 2 moons, named Phobos and Deimos.

Nobody knows for sure how Earths Moon formed, but a lot of scientists think that the Earth was hit by a big object 4.5 billion years ago. The impact was so big that lots of pieces of the Earth got thrown out into space. These pieces eventually became our moon.

The moons of mars are very small when compared to earths moon. They are believed to be from passing objects getting trapped by the gravitational pull of mars.

Saturn's rings are believed to be from a moon that got ripped apart by the strong gravitational force of Saturn. If a moon gets within a certain distance to a large planet this can happen. This distance is called the Roche limit and it depends on the sizes of the 2 objects.

These kinds of rings are seen on the larger planets because they have much stronger gravity and their Roche limit extends further into space than the smaller inner planets.

Answer 2:

Nobody knows. It may have been an accident. It may also be critical in making our solar system what it is. For example, Earth might not have life on it if not for the moon.

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