very powerful, strong piece. these impacts look great. these effects around them too. excellent job do you create these starmaps in the background by hand? photoshop or so? would be interesting what technique yuo use.
The cracking seems like it was created on a two dimensional plane rather than a three dimensional sphere. Also you could have intense burning debri in the upper atmosphere and dust clouds. When I first saw this it looked like the planet was getting hit by three objects. The impact shockwave is also too planar.
Brilliant job. I agree, spherize would help the cracking a great deal. Also, the shockwave on the left side seems out of place. See if you could get it to wrap the planet as well, or try bluring it a little more at the edges. The debris flying off the planet is perfect, and has a great look of motion to it. Good use of motion blur. Also, it's not like some pictures where the debris only comes in one size, you've got dust here as well as giant pieces and glowing debris. Excelent job.