User blog comment:BlackWizardZeref/Chapter 369: The Place Prayers Reach/@comment-3075024-20140131175528/@comment-7418318-20140202172832

Not really.

I can't believe that Gray would have the necessary range to call an existing comet, meteor or asteroid from all the way outside the planets gravitational field. And with him being unable to teleport it, he'd have to move it the entire way, which would mean a big time-delay even if he was able to do so in the first place.

On top of that, anything with enough ice in it to be manipulated by him would probably not survive the atmospheric entry anyway.

So the best he might be able to do would be to create something that looks like an ice meteor (but isn't really a Celestial Body) in mid-air and smash that onto his intended target. But then we don't know if Sema brought down an actual Celestial Body or "just" a look-a-like either.