Creating a planet Atmosphere (Blurry Edge)

Question

At the moment I work on a sci-fi short film and for this I created a planet in Blender Cycles. I'm almost finished and I'm pretty satisfied with the result. The only thing left to do is the blurry atmosphere of the planet. I've watched several tutorials how to create an atmosphere but it still has sharp edges. Also I can't create it with the compositing node because I have moving objects infront of the planet that shouldn't have blurry edges or glow. Now my question: Is there a possibility to achieve the "blurry edge" effect (see images) with a material node?

Thanks for your answers!

Answer 1

Final:

Overview:

In my setup I have used two objects - planet and rocket (created by t4k1t) and for lightning - Sun Lamp and Environment Map (HDRI).

Both objects are on separated layers.

In Render Layers tab you need to create two Render Layers and set it up accordingly to your object layers. Note that I've turned on Environment pass for Planet layer to have some background. You can skip this if you are using other method for it.

Turn on Transparent in Film section under Render tab.

After rendering your scene go to Composite and here are the blocks from screenshot explained:

1. Glare + Lens distortion for "blur" effect.
2. Combined and Inverted layers Alphas.
3. Combined layers.
4. Combined layers with Environment pass.

If you are not using HDRI map you can skip 2 and 4.