I think it would look better if the white cloudy area under the big planet was not so overpowering. That would balance it out more
I agree also the mountains in the front over to the right look like they need a little more blending. Other than that great job.
V1 has the sky that looks better. You should still fade those white clouds(under the big planet), they don't look right to me.
v3 is excellent. The lighting in the sky, and the way that you faded the stars and moons/planets into the clouds is really nice. I still think that the fore-most mountain should be darkened a tad more, and it might look good if you recolored the mountains with a faint blue, to really show that it is night time. Overall, great job.
You see, the mountains don't match still. If you know about light, you'll know it affects colors. Without light, we would have only one color. Without dark, we would only have one color. So having a yellowish type mountain indicates that there's a yellow light coming from the side. Do you intend on having a sun in the signature? If that happened, then there wouldn't be space theme, but a sky. So try gradient maps, or try colorizing the mountains a bit.