The inner planets of our solar system (Mercury, Venus, Earth, and Mars) are classified as terrestrial planets because they:

Question

Accepted Answer

Are composed primarily of rock and metal with solid surfaces. The inner four planets - Mercury, Venus, Earth, and Mars - are classified as terrestrial (Earth-like) planets because they are composed primarily of rock and metal, have solid surfaces, are relatively small and dense, and are located in the warmer inner region of the solar system. The term "terrestrial" comes from the Latin word for Earth (terra), reflecting the fact that these planets share fundamental compositional similarities with our home planet.

Thick gaseous atmospheres and ring systems characterize the outer gas giant planets (Jupiter and Saturn) and ice giants (Uranus and Neptune), not the terrestrial planets. While Venus has a thick atmosphere and Earth has a moderate one, Mercury has virtually no atmosphere, and Mars has a very thin one. The planets located beyond the asteroid belt are the outer planets, not the terrestrial planets. Most terrestrial planets have few or no moons: Mercury and Venus have none, Earth has one, and Mars has two small moons (Phobos and Deimos).

Understanding the basic organization of the solar system, including the distinction between terrestrial and gas giant planets, the asteroid belt, and other solar system bodies, is important for the CLEP Natural Sciences exam. The formation of the solar system from a spinning disk of gas and dust (the solar nebula hypothesis) explains why the rocky planets formed close to the Sun (where it was too hot for gases to condense) while the gas giants formed in the cooler outer regions where volatile compounds could accumulate.

CLEP Natural Sciences: Question of the Day

Get a free CLEP Natural Sciences question every day

Ready for the full CLEP Natural Sciences? Earn 6 college credits.