The planets differ greatly in density. The more distant and larger planets--Jupiter, Saturn, Uranus and Neptune--have densities equal to or less than that of the sun. The densities of the inner planets--Mercury, Venus, Earth and Mars--are, relatively, extremely high, the density of the Earth's core being about that of meteoric iron. The densities of Mercury and Venus are slightly less than that of the earth and the densities of Mars and the moon about equal to that of the earth's crust.