Most asteroids are located in the asteroid belt between Mars and Jupiter.
Asteroids are much smaller than the Earth or the Moon.
The largest one is called Ceres and it is about 933 kilometers across. All other known asteroids are less than 340 km in diameter. When comets approach the sun, they begin to warm and melt. Evaporating gases and dust that sputter off the surface of a comet create long tails that can sometimes be seen from Earth. Comet dust forms a cloud of debris that trails the comet in its orbit around the sun.