The boundary that separates the inner and outer solar system is commonly identified as the asteroid belt. This region lies between the orbits of Mars and Jupiter and is composed of numerous rocky and metallic bodies, which are the remnants from the early solar system.
The inner solar system consists of the terrestrial planets—Mercury, Venus, Earth, and Mars—characterized by their rocky surfaces and relatively small sizes. This region is closer to the Sun, where temperatures are higher, causing lighter elements and gases to be blown away, leaving behind heavier materials.
In contrast, the outer solar system is home to the gas giants—Jupiter, Saturn, Uranus, and Neptune. These planets are much larger and composed predominantly of gases and ices due to the cooler temperatures and ample availability of these lighter materials at greater distances from the Sun.
The asteroid belt not only serves as a physical barrier between these two distinct regions but also marks a significant contrast in planetary composition and characteristics, underscoring the diverse nature of our solar system.