Spell Comet

You named that spell Comet. Comets do not enter our atmosphere. The correct word is Meteorite. Even if you say that with great magic you pick up a comet and you land it on the exile enemies, the moment it enters our atmosphere it becomes a Meteor and the moment it hits, it becomes a meteorite.
(I am fun at parties)

They called it a comet specifically because it's made of Ice. Instead of making a comet enter the atmosphere and become a meteorite (which would make the Ice melt) the Sorceress teleports the comet with magic.