Definition
A terrestrial planet is a type of planet mainly composed of silicate rocks and metals. It has a solid surface and a defined crust, unlike gas giants or icy planets. These planets form in the inner regions of star systems, where heavy elements are more abundant.
Internal structure
The typical structure of a terrestrial planet includes a central metallic core, usually made of iron and nickel, surrounded by a rocky mantle and a solid crust. This layering results from gravitational differentiation during the early stages of planetary formation. Some terrestrial planets also have a secondary atmosphere formed by degassing or capture of external compounds.
Surface and composition
The surfaces of terrestrial planets show great variety in relief: mountains, plains, impact craters, and tectonic structures. Their chemical composition includes silicate minerals, metal oxides, and sometimes traces of volatile compounds. The presence or absence of liquid water depends on the distance from the star and the atmospheric pressure.
Role in star system
Terrestrial planets may exhibit active geological processes such as volcanism or plate tectonics, which influence their atmosphere and evolution. Their role in the star system relates to gravitational interactions with other bodies and their ability to stabilize surrounding orbits.
Variation and boundaries
The classification as a terrestrial planet is based on structure and composition, but there are borderline cases with ice-rich or hybrid exoplanets. Additionally, their mass varies within limits consistent with a rocky structure without gravitational collapse into a fluid sphere.