This Cassini photo of Saturn was taken July 8, 2007 from a distance of 2.9 million kilometers. Both circular and linear cloud features are visible. Each pixel represents an area 17 kilometers across. Saturn is the planet with the lowest density in our Solar System, barely 0.7 g/cc or the density of a milkshake. In a giant tub of water the planet would easily float.
Lowell and Palomar Observatories have jointly discovered the largest known planet yet found, orbiting a star 1400 light-years away. The new world, called TrES-4, has a diameter 1.7 times that of Jupiter. Its density is half that of Saturn, or 1/3 the density of liquid water! The temperature of TrES-4 is estimated at 2300 degrees Celsius, so hot that the surface should boil off. Scientists are at a loss to explain how such a world can exist.
It is not widely mentioned in astronomy textbooks that scientists can't explain how ANY planets formed. The standard explanation is that planets condensed from gas clouds, but tiny particles colliding at orbital velocities simply will not stick together. Particles would need the mass of mountains to attract matter. Recently many "hot Jupiters" have been discovered orbiting so close to their stars that they should boil away.
The Big Bang created billions of tiny singularities, many with the mass of mountains. The solar system was probably started when some of these tiny Black Holes collided with gas clouds. If planets formed in this manner, presence of the Black Hole would hold the gas together and prevent it from boiling off. The Black Hole's gravity would allow the planet to have an extremely low density.
Writing this makes one very hungry. It will take a long time for all this to be accepted, but that is time to enjoy plenty of milkshakes!