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The Inner Solar System

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Exploring the inner Solar System reveals the unique characteristics of the terrestrial planets—Mercury, Venus, Earth, and Mars—and the intriguing asteroid belt. These planets are known for their solid surfaces, geological activity, and varying atmospheres, with Earth being the only one to support life. The asteroid belt, filled with remnants from the Solar System's formation, offers insight into planetary evolution and the potential origins of Earth's water.

Exploring the Inner Solar System

The inner Solar System is defined by the four terrestrial planets—Mercury, Venus, Earth, and Mars—and the asteroid belt, all located within the frost line, which is less than 5 astronomical units (AU) from the Sun. This region is much smaller than the vast distance separating the gas giants Jupiter and Saturn. The terrestrial planets are primarily composed of silicate rocks and metals, which contribute to their dense and rocky nature. They are generally devoid of extensive moon systems and rings, have achieved a spherical shape through hydrostatic equilibrium, and exhibit differentiated interiors with distinct layers.
Terrestrial planets of the solar system in a row: gray and cratered Mercury, pale yellow and cloudy Venus, blue and green Earth, red Mars.

Common Traits of Terrestrial Planets

The terrestrial planets share a number of characteristics, including a solid surface composed of silicate minerals and a metallic core, typically iron and nickel. Venus, Earth, and Mars have significant atmospheres that drive weather patterns, while Mercury's is extremely tenuous. All four planets show evidence of geological activity, such as impact craters, volcanism, and tectonics. It is important to distinguish between "inner planets," which refers to all terrestrial planets, and "inferior planets," a term used specifically for Mercury and Venus, which orbit closer to the Sun than Earth.

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The ______ planets, made up mostly of silicate rocks and metals, are dense and lack large ______ systems and rings.




Unlike the vast expanse between ______ and ______, the inner Solar System is relatively small.




The inner planets, which have achieved a spherical shape, are in ______ equilibrium and have ______ interiors.




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