Caus with the speed of the astoroid and when it first coes into Earth's atmoshpere it will catch on 火, 消防 and mely the ice on it thats why it makes and big boom when it crashes.
Firebenders have the ability to 马具, 线束 the energy from the comet and turn it into firebending just like what waterbenders can do during the full moon. The distinction between asteroids and comets is made on visual appearance: Comets 显示 a perceptible coma while asteroids do not. Comets do not burn up in the atmosphere otherwise Sozin's comet could not be seen every 100 years.
