Why are inner planets smaller than outer planets?

Our solar system started as a large cloud of dust and gas called Nebula. Over many billions of years, the immense gravity of this large cloud caused the dust and gas to slowly fall inward towards its center. The center continued to collect more and more matter, growing larger and larger. read more

The planets closest to the Sun, (Mercury, Venus, Earth and Mars) are called the terrestrial planets. They are small, dense, rocky planets. The outer planets (Jupiter, Saturn, Uranus and Neptune) are called the Jovian Planets. They are large and made up of gas. read more

Best Answer: Material in the inner solar system is less abundant than the outer solar system. There are many planets that formed in the inner solar system. They are wiped out due to gravitational disturbances and collision to other proto-planets. Debris are swept off by the 4 surviving planets: Mercury, Venus, Earth and Mars. read more

These planets were more massive than the inner planets and were able to attract large amounts of hydrogen and helium, which is why they are composed mainly of hydrogen and helium, the most abundant elements in the solar system, and in the universe. read more