Which planet has the lowest density?

Saturn is a gas giant made mostly of hydrogen and helium, and although it is huge, its material is spread out over an enormous volume. Its average density is about 0.69 grams per cubic centimetre, while liquid water is 1 gram per cubic centimetre. This is why Saturn is often said to be able to float in a bathtub big enough to hold it, although no such bathtub could exist. Saturn spins so fast, once every 10.7 hours or so, that it bulges noticeably at the equator. By contrast, Earth is the densest planet, at about 5.5 grams per cubic centimetre.