Thats good progress there, spiffy image
first of, I would eliminate any sort of glow or flare from infront of the planet. It doesnt make sense that an exploding planet would have a large central flare type thing
secondly, you need to roughen up th edges of the planet, to make it look less like a perfect circle. this can be done by simply using an irregular (you know, with uneven edges) photoshop brush and doing the edges of the planet a bit. dont go overboard though
and lastly, you need to create some "veins" on the planet, to make it look like its falling apart. I tried doing this with a standard "get the poly lasso tool and go crazy, then slide over a few pixels" method but it didnt look good. So I guess you havr to figure out how to do that n your own. The colour that is seen through the cracks should be the same as the colour behind the planet, so it would be useful if you still have the planet as a seperate layer..