The size difference between the Jovian and terrestrial planets in the solar system occurs because of the planets' proximity to the Sun and chemical composition. Jovian planets lie beyond the frost line, which separates the four terrestrial planets from the gaseous Jovian planets. Despite residing farther from the Sun, the Jovian planets have larger sizes than terrestrial planets due to their gaseous compositions and stronger gravitational fields, which help pull objects to their surfaces, ultimately increasing their sizes.
Planets classified as Jovian include Saturn, Uranus, Venus and Neptune. These planets contain different materials within their cores, formed from various elements. Their inner cores mostly contain ice and solid particles. The surrounding layers, however, form from gases.
They are derived primarily from hydrogen and helium, along with compounds containing these elements. Unlike the organic materials that form the terrestrial planets, helium and hydrogen never condense in the atmospheres of the Jovian planets. Instead, the gases accumulate, letting the surface sizes of outer planets expand infinitely.
These planets have greater gravitational pulls as their sizes increase. This, in turn, attracts and retains even more gaseous molecules. Jovian planets, also called gas giants, sometimes accumulate gases beyond their carrying capacity. This creates a gravitational collapse, where planets suddenly heat up, flatten and change shape.