Astronomy Practice Exam 2025 – Complete Preparation Guide

The distinguishing characteristic of the outer planets compared to terrestrial planets is that the outer planets are mostly gas giants. This classification includes Jupiter, Saturn, Uranus, and Neptune, which are primarily composed of hydrogen and helium, along with other gases and ices. Unlike terrestrial planets such as Earth, Mars, Venus, and Mercury, which have solid, rocky surfaces, the outer planets lack a well-defined surface and instead have deep atmospheres and high-pressure cores.

This fundamental difference in composition significantly affects their physical properties, including size, density, and atmospheric conditions. The gas giants are much larger in size and possess extensive systems of rings and moons, further distinguishing them from the smaller, rocky terrestrial planets. The presence of these gaseous envelopes contributes to the dynamic weather patterns observed on these planets, such as the Great Red Spot on Jupiter.

Understanding this difference gives insight into the formation and evolution of our solar system, as the outer planets formed in the colder regions beyond the frost line, allowing them to accumulate more gas and ice compared to their terrestrial counterparts, which formed closer to the Sun.