What distinguishes terrestrial planets from gas giants?

Terrestrial planets are primarily composed of rock and metal, while gas giants are mostly made up of hydrogen and helium.

Terrestrial planets, also known as rocky planets, are characterised by their solid surfaces made up of silicate rocks or metals. These planets are similar to Earth in terms of their composition and size. The terrestrial planets in our solar system are Mercury, Venus, Earth, and Mars. They have a compact, solid surface with mountains, valleys, and craters. These planets also have a core, mantle, and crust, much like the Earth.

On the other hand, gas giants, also known as Jovian planets, are primarily composed of hydrogen and helium, similar to the Sun. They are much larger than terrestrial planets and lack a solid surface. The gas giants in our solar system are Jupiter and Saturn. These planets are surrounded by numerous moons and have a strong magnetic field. They are known for their ring systems, which are made up of dust and other small particles.

Another key difference between the two types of planets is their atmospheric composition. Terrestrial planets have very thin atmospheres, while gas giants have incredibly thick atmospheres that are made up mostly of hydrogen and helium, with traces of methane, ammonia, water and other compounds.

In terms of location within the solar system, terrestrial planets are found closer to the Sun, while gas giants are located further away. This is known as the frost line theory, which suggests that the colder temperatures further from the Sun allowed volatile compounds such as water, ammonia, and methane to condense and form the gas giants.

Lastly, the formation process of these planets also differs. Terrestrial planets are believed to have formed through the process of accretion, where dust and rock in the early solar system collided and stuck together. Gas giants, however, are thought to have formed from the gas and dust that surrounded the young Sun, which collapsed under its own gravity to form a planetary core, which then captured the surrounding gas and dust.