Jupiter.
The phrase "least dense planet" refers simply to the planet with the lowest density, which is the planet's mass divided by its volume. In our solar system, Saturn is the least dense planet with a density of roughly 0.7 (water, by comparison, has a density of 1, or 1 gram per cubic centimeter). This is attributed to its large outer envelope of gas - although it is thought to have a denser rocky core.
The planet with the least mass and smallest is Mercury. The planet with the lowest density is Saturn
Mars is the least dense of the rocky planets.
Saturn is the least dense planet, only 0.7 g/cc on average (less than water's density). If you could put Saturn in bathwater, it would float.
Density of a planet = (Planet's mass) divided by (Planet's volume)
Saturn is the least dense of the gas giants, even out of all of the planets in our solar system. Its average density is around 0.7 g/cc (less than water).
The least small and least rocky planet is probably Saturn. Saturn - as a whole planet - has a density less than water, meaning that if you could find a lake big enough to put it in, Saturn would float!
Saturn will float in ocean as it has least density of 0.70 gm/cm^3..
Mercury has the second greatest density (behind Earth), with a density of 5.43 g/cm3 (5430 kg/m3).
Mercury. Although it has a high density, it's the smallest planet and least massive overall.
Certainly - all matter has density. The density of a gas planet would probably be less than that of a more solid planet but it would still have a non-zero density.
Mercury has the second lowest density of any planet in the solar system. Saturn has the lowest density of any other planet.