Low densities despite large size, close to that of water. Gassy balls streaked with bands of clouds. Most pronounced on Jupiter, less so on Saturn and Neptune, least on Uranus. Rotation Rapid rotation, range of 10 to 17 hours. If the planets were in solid-body rotation , all parts would take the same time to get around.
Differential rotation is only possible if the planet is fluid.
Most abundant elements are Hydrogen and helium just as in sun. All the Jovian planets have rings made of small independently orbiting particles and All have extensive systems of large and small satellites. We will discuss these in a separate lecture. Rocky cores form by accretion in early solar nebula. Reach about the size of the earth.