Done in Blender (color correction, layer composition, rendering in Cycles), Krita (little mistakes/glithes correction, smoke edition) and Perfect Effects 8 Free (color correction, composition, contrast improvement and other effects).
I like what you are doing, and it shows a lot of promise; although mankind’s future looks much less promising. :eek:
I hate glow; in space, they can’t hear you scream. For the same reason glow and glare are limited to there being something present or in the path of the light travelling to the viewer (or camera). So if you’re doing glare then make sure it is believable; although there is nothing wrong with artistic effect and can be great but you really need to sell the idea then.
For me the light looks wrong; half the earth and moon are in light or shadow. The asteroid is all in shadow, or all in subdued light perhaps. That looks very unrealistic; admittedly what would light up would vary as the object rotates, but there should be some delineation between light and dark.
The green on the asteroid suggests copper to me; iron based asteroids certainly exist, otherwise they are mixtures of ice and dirt, so I’d go with that. If you want to stick with those colours then the story your image is telling needs to take that into consideration.
I would also expect to see more dust, think a comet-tail as it gets closer to the sun; it has been close enough to the sun for some time now, at least looking at it in relation to how close to earth it is now.