Why are terrestrial planets smaller and denser?

Answer 1

Terrestrial, or mostly solid, planets are much denser than Jovian, or gas, planets. This is because they, as you may have noticed, are much closer to the Sun. They actually used to have gas surrounding them, though because of the Sun's powerful solar rays, were blown off of their surfaces. Solar rays are also gradually affecting the gas planets. Each year, 2 centimeters of Jupiter's surface is blown off.

Answer 2

Terrestrial planets are denser than gas giants because they are made largely of rock and metal, which is denser than the hydrogen and helium that makes up the bulk of the gas giants. They are smaller because they largely lack those lighter materials, which account for most of the solar system's mass, even excluding the sun.

Answer 3

They are mostly rock. The gas giants have solid - usually rocky - cores, but they are mostly gas. Rock is much more dense than gas.

Answer 4

Because they are composed of metals and rock rather than gases.