for the stars, you could consider using a skybox, or sprites, like Jack said.

I think the atmosphere thing can be done with sprites too.
Just make a spherical sprite, just some bigger than the planet.
make it the color you want the atmosphere to be, and place it at the center of the planet. you will see it's borders, because it is bigger than the planet.
every frame you should then let the sprite face the camera.
I haven't tried it, but it will work, although I do not know if it will look good.