Hey Pinworm -
This is how I would setup an atmosphere shader for a planet. I would use two spheres one which is set to a slightly larger scale and with the following materials applied.
Atmosphere Material:
Planet Texture:
Final Results:
This may not be exactly what you are looking for and I would be happy to update this to get more of the results you are looking for, but I would need a screenshot of what you currently have.
Thank You
Eric Ketchum