looks great.
The only thing I see is the night time with the star map- it looks like your in outer-space.
I would say- look at these images below
Mainly the number of stars is what i believe is creating the image of the planet has not atmosphere.
From looking at the images I posted. It looks like the sky line/horizon as a glow. This and a few less stars might help.
keep up the great work
http://www.dimijianimages.com/More-p...ar-gallery.htm
http://2.bp.blogspot.com/-fNA3tSDc8o...y-5%5B1%5D.jpg
http://img.ezinemark.com/imagemanage...-of-spain.jpeg