I don't know whether atmosphere around (or inside) arbitrary objects or shapes will be possible, at least initially, but we do hope to allow modification of atmosphere density by a shader, so that you could vary atmospheric density or other settings (such as Red Decay) across the planet. In general I think the visible effect of this from orbit would be minimal, but it would at least allow you to have complete planets that behave in a more realistic way.
- Oshyan