Both comets and asteroids are relatively small objects that orbit the sun were formed in the early days of our solar system. But there the likeness ends. Comets, often called dirty snowballs, are made up primarily of ice with dust and rock particles mixed in. When comets draw closer to the sun, they begin to vaporize, and a halo, called a coma, forms around them. High-speed solar winds produce the long tails that give comets their distinctive look.
Photos of Asteroid Vesta was taken by NASA and image of Comet taken by NASA spacecraft.
Asteroids come in all shapes and sizes and are composed of rock and metal, leftover scraps from when the solar system formed. Most asteroids orbit in the asteroid belt between Mars and Jupiter.