Why are the inner planets dense and small while the outer planets are gas giants?

Answer 1

Gas Giants have mostly Hydrogen gas which is the lightest element, so in fact gas giants are in overall density the lightest of all the planets. Jupiter is 318 times the mass of the whole Earth, and roughly 99% of that mass is Hydrogen.

At their cores they may be very dense because of great pressure, but it is still mostly Hydrogen and not as dense as a rocky planet. Gas Giant densities may be very different from each other because along with the Hydrogen they may have more Helium or a larger core of ice and/or rock.

Neptune's overall density is 1.638 g/cm³ - 30% as dense as Earth

Jupiter's overall density is 1.326 g/cm³ - 24% as dense as Earth

Uranus's overall density is 1.27 g/cm³ - 23% as dense as Earth

Saturn's overall density is 0.687 g/cm³ - 12% as dense as Earth

Earth's overall density is 5.515 g/cm3

Answer 2

The likely reason proposed by scientists is that the smaller planets accreted from dense material closer to the Sun that had to revolve faster to maintain its orbit.

Although the actual result is not clear, any gas giant close to the Sun would have been heated to the point that it lost most of its lighter elements to space. Jupiter, for example, would likely lose a large percentage of its hydrogen if it were as close as Earth or Venus.

Dwarf planets far from the Sun, such as Pluto and Eris, contain a lot of frozen gases and are more closely related to asteroids and comets.

Answer 3

gravity keeps the gas giants' gases from escaping

Answer 4

Gas Planets are dense inside because the gas becomes dense because it has lots of mass.

Answer 5

gravity keeps the gas giants planets gases from escaping so they have thick atmosphere

Answer 6

gas giants have so much gas that they came up with the name,gas giants

Answer 7

These gas giants have a very high gravity.