They are bits of rock and iron orbiting around the sun. Meteors may be the size of a grain of sand. The biggest asteroid yet discovered is called Ceres. Its diameter is 650 miles long. There is more than 7000 asteroids known of, but there are probably more that we can not see.
Comets are blocks of frozen ice mixed with cosmic dust.
It is estimated there to be a trillion more comets on the edge of the solar system. When a comet goes by the sun it transforms from a sold form to gases. Also the tail of a comet faces a way from the sun at all times. The most famous comet is Halleys Comet. Fire balls are large meteors that pass close to Earth.