A quick 5 minute painting to sketch out my ideas.

Created the basic stars using noise filter at 15% and levels adjustment. Did this twice on 2 separate layers and enlarged one layer. masked off the smaller layer to give more dense stars. 2 larger stars are done with the lens flare filter.

Cut out various parts of the source image to create landscape.

Created the background mountains using more parts of source image. Painted horizon green using a soft brush to give the sulphurous haze. Brought in the space sky (flipped so large star appears to cast diagonal light beams on mid ground).A mixture of Hue/Saturation/Colorize and burn to give red glow. Also started adding some highlights to foreground. Highlights are white painted on if they are coming from left hand star, and a mixture of burn and red painted on, if they are caused by underground glow.

Roughed out the space craft in grey.

Tidied up the lines of the space craft using pen tool, and added shading. Started to rough out cloud/nebula formation using low opacity soft edged brush.

Decided I wanted this picture to be more about the landscape than the space craft, so shrunk space craft down and moved it's position. Added more cloud detail.

Finished cloud detail and lowered opacity to give more subtle effect. Added a few larger stars using soft had edged brush, with outer glow added.