What Planet Has a Density Less Than Water?

Water has a greater density than only the planet Saturn. All of the planets in the solar system have a density that is superior to that of Saturn. Saturn is one of the gas giants, made largely of hydrogen, and the second largest planet in the solar system.

Saturn is close to 800 times larger than Earth, making it the most dense of all planets. Only the planet Jupiter has a greater mass than Saturn. Jupiter has the second lowest density in the solar system, and has the same composition, hydrogen and helium, as the least dense planet. The large degree of gas composition of Saturn and Jupiter is responsible for the low densities.