Which planet has the lowest density?

Saturn has the lowest density of all the planets in the Solar System. The density of this gas giant is 0.687 gram per cubic centimetre.

Water has a density of 1 gram per cubic centimetre, so Saturn is less dense than water. This means that Saturn would float if there were a bathtub big enough to hold the planet. In contrast to Saturn, Earth is the densest planet with a density of 5.51 grams per cubic centimetre. Saturn is made up of mostly hydrogen and helium. It is the second largest planet after Jupiter and is big enough to contain over 760 Earths. The four inner planets of the Solar System are denser than the outer gas giants and are made up of rocks and heavy metals.