Mar's atmosphere is tricky, because it's not just a solid red atmosphere. Because of it's composition and density, the boundaries, especially at the poles have blues where density is thicker. This is not so easy to do in Terragen as a thought. Lol
This image is looking down from somewhat the north pole of Mars, though it's mostly obscured by shadows.
Mars textures needed more help in 3D then just a texture map, so Ambient Occlusion, Edges, and Reflectivity Maps were created.