What is the difference between an asteroid and a comet?
Both Asteroids and Comets are left over debris from the formation of the Solar System.
Asteroid are mainly composed of rock and metals. They orbit they sun on a relatively closer in orbit than the comets. Most Asteroids are generally found in the region of space between Jupiter and Neptune in the Asteroid Belts.
comets on the other hand are composed of ice. Along with ice they also have some other elements like Methane and Ammonia but all of them in solid form, in the form of ice. As Comets come close to Earth these gases transform from solid to gases, a process called Sublimation that is why you see long tails. Comets are thought to be originating from two different regions in Space. One region is just beyond the orbit of Neptune starting at about 4.5 Billion km from the Sun in the Kuiper Belt. These comets are called Short Period comets and have orbits of less than 200 years. The Other type of comets originate from a more distant region in Space called the Oort Cloud. These Comets are called Long Term comets and have orbit more than 200 years. It is believed that Oort Cloud consists of a trillion icy bodies.