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Three of the four inner planets (Venus, Earth, and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. [91] Mercury (0.31–0.59 AU from the Sun) [D 6] is the smallest planet in the Solar System.
Currently, many planetary scientists think that the Solar System might have looked very different after its initial formation: several objects at least as massive as Mercury may have been present in the inner Solar System, the outer Solar System may have been much more compact than it is now, and the Kuiper belt may have been much closer to the ...
The differences between the inner planets are primarily the consequence of different degrees of protoplanetary compression. There are two types of responses to decompression-driven planetary volume increases: cracks, which were formed to increase surface area, and folding, which created mountain ranges to accommodate changes in curvature.
Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets.
Inferior/interior and superior are different from the terms inner planet and outer planet, which designate those planets that lie inside the asteroid belt and those that lie outside it, respectively. Inferior planet is also different from minor planet or dwarf planet. Superior planet is also different from gas giant.
Giant planets can significantly influence terrestrial planet formation. The presence of giants tends to increase eccentricities and inclinations (see Kozai mechanism) of planetesimals and embryos in the terrestrial planet region (inside 4 AU in the Solar System). [62] [66] If giant planets form too early, they can slow or prevent inner planet ...
In the warmer inner Solar System, planetesimals formed from rocks and metals cooked billions of years ago in the cores of massive stars. These elements constituted only 0.6% of the material in the solar nebula. That is why the terrestrial planets could not grow very large and could not exert a strong pull on hydrogen and helium gas. [3]
The internal structure of the inner planets. The internal structure of the outer planets. A planetary core consists of the innermost layers of a planet. [1] Cores may be entirely liquid, or a mixture of solid and liquid layers as is the case in the Earth. [2]