The uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. It would thus include both terrestrial and icy planets. The name Terran world has been suggested to define all solid worlds (bodies assuming a rounded shape), without regard to their composition. Jupiter's Ganymede, though icy, does have a metallic core like the Moon, Io, Europa, and the terrestrial planets. Titan even has surface bodies of liquid, albeit liquid methane rather than water. Ceres, Dione, Miranda, Ariel, Triton, and Pluto).

Some of these bodies are known to have subsurface hydrospheres (Ganymede, Callisto, Enceladus, and Titan), like Europa, and it is also possible for some others (e.g. Ganymede, Callisto, Titan, and Triton) or even primarily ice (e.g. It also includes the other round moons, which are ice-rock (e.g. These include the dwarf planets, such as Ceres, Pluto and Eris, which are found today only in the regions beyond the formation snow line where water ice was stable under direct sunlight in the early Solar System. They are similar to terrestrial planets in that they have a solid surface, but are composed of ice and rock rather than of rock and metal. The other round bodies from the asteroid belt outward are geophysically icy planets. Many S-type and M-type asteroids may be such fragments. Some other protoplanets began to accrete and differentiate, but suffered catastrophic collisions that left only a metallic or rocky core, like 16 Psyche or 8 Flora respectively. These two were likely both dwarf planets in the past, but have been battered out of equilibrium shapes by impacts. Europa is believed to have an active hydrosphere under its ice layer.Дuring the formation of the Solar System, there were many terrestrial planetesimals and proto-planets, but most merged with or were ejected by the four terrestrial planets, leaving only Pallas and Vesta to survive more or less intact. Among these bodies, only the Earth has an active surface hydrosphere. The Earth's Moon as well as Jupiter's moons Io and Europa would also count geophysically. The Solar System has four terrestrial planets under the dynamical definition: Mercury, Venus, Earth and Mars.

From left to right: Earth, Mars, Venus and Mercury. This contrasts with the outer, giant planets, whose atmospheres are primary primary atmospheres were captured directly from the original solar nebula. Terrestrial planets have secondary atmospheres, generated by volcanic out-gassing or from comet impact debris. Terrestrial planets can have surface structures such as canyons, craters, mountains, volcanoes, and others, depending on the presence of an erosive liquid and / or tectonic activity. Another Jovian moon Europa has a similar density but has a significant ice layer on the surface: for this reason, it is sometimes considered an icy planet instead. The Earth's Moon and Jupiter's moon Io have similar structures to the terrestrial planets, but Earth's Moon has a much smaller iron core. Another rocky asteroid 2 Pallas is about the same size as Vesta, but is significantly less dense it appears to have never differentiated a core and a mantle. The large rocky asteroid 4 Vesta has a similar structure possibly so does the smaller one 21 Lutetia. Terrestrial planets have a solid planetary surface, making them substantially different from the larger gaseous planets, which are composed mostly of some combination of hydrogen, helium, and water existing in various physical states.ДЄll terrestrial planets in the Solar System have the same basic structure, such as a central metallic core (mostly iron) with a surrounding silicate mantle. The terms 'terrestrial planet' and 'telluric planet' are derived from Latin words for Earth ( Terra and Tellus), as these planets are, in terms of structure, Earth-like. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites вЂ“ Earth's Moon, Io, and sometimes Europa вЂ“ may also be considered terrestrial planets and so may be the rocky protoplanet-asteroids Pallas and Vesta. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun, i.e. The terrestrial planets of the Solar System: Mercury, Venus, Earth and Mars, sized to scaleДЄ terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals.

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