Terrestrial planet and gas giant: what are the differences?

Astronomers distinguish two main families of planets: "terrestrial" planets and "gaseous" planets. Mercury, Venus, Earth, and Mars are terrestrial planets in the Solar System, while Jupiter, Saturn, Uranus, and Neptune are gas giants.

Formation of terrestrial and gaseous planets

The primitive gas nebula that gave birth to the planets of the Solar System was mostly made up of hydrogen and helium, just like the rest of the universe (hydrogen being the most abundant element). However, as a result of various physical phenomena, these elements migrated outward from the system, leaving almost only heavier elements such as silicon, carbon, or iron inside.

Composition and density of planets

Thus, the inner planets of the Solar System, the terrestrial planets, are essentially made up of minerals and rocks organized into three concentric envelopes: the core, the mantle, and the crust. Their density is between 4 and 5.5.

The gas giants, on the other hand, formed from the available gases at a distance from the Sun. They have a very small silicate core and a density close to that of water, between about 0.70 and 1.70. Temperatures and pressures increase as you move deeper toward their core.

Different sizes and rotational periods

Deprived of most of the material available in the primitive nebula, terrestrial planets are modest in size compared to gas giants, also known as giant planets: a little over 6,000 km in radius for Earth compared to about 70,000 km for Jupiter.

Due to their modest size, terrestrial planets, unlike gas giants, have not been able to adorn themselves with rings or retain many satellites.

The last notable difference between terrestrial planets and gas giants is their rotational period. For example, while Earth takes about 24 hours to make one rotation on its axis, Jupiter has a rotational period of only 10 hours!