I cut the shell and played with free transform and warp tools
step 2 of 7
I made small flowers from distorted shell, used warp tool for it. I used eraser to blend small flowers with big one
step 3 of 7
I placed big shells, and add lights and shadows with dodge and burn tools
step 4 of 7
I made 2 pathes and fill them with gradient from white to transparent
step 5 of 7
Than I merge all layers with lines and apply gaussian blur. With soft big brush I add sun.
step 6 of 7
Than I add stars with star brush with different sizes.
step 7 of 7
Than I made planet. I made circle selection on big shell, cut it to new layer,used spherize 50%, made it smaller and apply inner shadow. Than I add small circle around planet.