Final answer:
Asteroids are rocky and mainly found in the asteroid belt, while comets are icy and have more eccentric orbits which can create a gas head and tail when approaching the Sun.
Step-by-step explanation:
The main difference between asteroids and comets is that asteroids tend to be rocky, while comets tend to be icy. This composition difference is critical because it affects how these objects behave when they come close to the Sun.
Asteroids, which are typically found in the asteroid belt between Mars and Jupiter, are mostly composed of carbonaceous materials, stony or metallic elements, and lack the volatile materials that create the characteristic tail of comets.
On the other hand, comets have orbits with larger size and greater eccentricity, spending most of their time far from the Sun. However, as they near perihelion, comets can brighten dramatically due to the sublimation of their icy components, creating a head of gas and a tail that can be millions of kilometers long.