* Mercury: 4,879 km (3,031 mi)

* Venus: 12,104 km (7,521 mi)

* Earth: 12,756 km (7,926 mi)

* Mars: 6,792 km (4,220 mi)

Outer Planets

* Jupiter: 142,984 km (88,846 mi)

* Saturn: 120,536 km (74,898 mi)

* Uranus: 51,118 km (31,763 mi)

* Neptune: 49,528 km (30,774 mi)

As you can see, the outer planets are much larger than the inner planets. Jupiter, the largest planet in the solar system, is over 11 times the diameter of Earth. Saturn, the second-largest planet, is over 9 times the diameter of Earth. Uranus and Neptune are both over 4 times the diameter of Earth.

The reason for this difference in size has to do with the formation of the solar system. The inner planets formed closer to the sun, where the temperature was hotter. This heat prevented them from accumulating as much gas and ice as the outer planets, which formed further from the sun. As a result, the inner planets are smaller and denser than the outer planets.