Astronomy Practice Exam 2025 – Complete Preparation Guide

The distinction between comets and asteroids is primarily based on their composition. Comets are predominantly composed of ice, dust, and rocky material, which gives them their characteristic tail and coma when they approach the Sun. This icy composition is what allows comets to be more active and display visible tails formed by gas and dust as they heat up and release materials due to the proximity to solar radiation.

In contrast, asteroids are primarily rocky and metallic. They are found mostly in the asteroid belt between Mars and Jupiter and do not typically exhibit the same kind of activity as comets because they lack significant amounts of volatile materials that can vaporize.

This fundamental difference in composition is essential in understanding the behavior and characteristics of these celestial bodies. The other options do not accurately reflect the nature of comets and asteroids or misrepresent their physical characteristics, as comets cannot be classified as gaseous or that asteroids are strictly large or that they can orbit planets; their orbits can vary widely across the solar system.