I was just browsing the Ray Dream Handbook (that's about four years old now) and saw a tutorial for making a glowing atmosphere for a planet. It's a little different than the Aura. You put a bulb light at the center of the planet sphere, and give it a Light Sphere effect with a radius slightly larger than the planet's radius. Turn on turbulence, etc. Never tried it - I wonder how it turns out? Beautiful render.