Density is a key measure of the material which comprises a planet. It is a measure of how much matter is packed into a volume of space.
| Water has a density of 1 gm/cm 3 |
| Iron has a density of 7.8 gm/cm 3 |
| Rocks have a density of 2-4 gm/cm 3 . |
So, by knowing the density of a planet, one can roughly determine the internal composition. The Earth has a density of 5.5 gm/cm3 whereas Jupiter has a density of 1.3 gm/cm3 . What does that tell you about the difference in compositions of these two planets?
