Here's why:

* Density is calculated by dividing an object's mass by its volume.

* Earth has a high density because it's made up of a dense iron core and a mantle composed of heavier elements like silicon, oxygen, and magnesium.

* While planets like Jupiter and Saturn have larger masses, they are mostly composed of lighter elements like hydrogen and helium, giving them lower densities.

Let me know if you'd like to learn more about the planets and their compositions!