Notes

The terrestrial planets make up the inner solar system. They form a related group of rocky worlds that are very different from the gas planets of the outer solar system and the icy bodies of the Kuiper belt.

Although Earth's Moon is not technically a planet, it is usually organized among the terrestrial planets because its size, composition, and history are related to those of Mercury, Venus, Earth, and Mars.

Venus and Earth are very similar in size. Mars is half their size, and Mercury is even smaller (it's about the same size as Saturn's moon Titan and Jupiter's moon Ganymede).

The Moon is one quarter the diameter of Earth, or one half the diameter of Mars.

On average, Mercury is only about a third as far from the Sun as Earth is. That makes the Sun 11 times hotter at Mercury than at Earth. Mars's distance from the Sun is 50% greater than Earth's, which makes the Sun only half as strong there. Venus' and Earth's orbits are almost perfectly circular, while Mercury's and Mars' are noticeably elliptical.

That makes Mercury's and Mars' distance from the Sun vary more over the course of one year than Earth's and Venus'.