[Answer] The Earth is the densest planet in the Solar System, at 5.51 g/cm3, as others have correctly answered. The reason for this high density is the apparent collision, over four billion years ago, of a proto-Earth and a hypothetical Mars-sized planet Theia

Step 1 : Introduction to the question "The Earth is the densest planet in the Solar System, at 5.51 g/cm3, as others have correctly answered. The reason for this high density is the apparent collision, over four billion years ago, of a proto-Earth and a hypothetical Mars-sized planet Theia"

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