Duplicate this layer - you will need a copy of it a bit later. (hide duplicated layer for now).
Rasterize original layer.
Open this layer's blending options (layer style) and add small outer glow and big inner glow. Add a bit of noise (Filter - Noise - Add noise).
future steps will show that the planet needs to be darker :-). So using Hue/Saturation (Ctrl-U), make planet darker and more saturated (you can always adjust it later as well).
To add some nice light reflection, take a copy of planet shape (circle), switch to Path selection tool (A), select circle shape, copy-paste (Ctrl-C, Ctrl-V), move copied circle a bit down and change its mode to "substract". Then, change layer's blend mode to "overlay".
Now, we need much more outer glow from our planet! To add it, select layer with planet and duplicate it again. Clear layer style, so that it has not outer and inner glows.
To go filter - blur - gaussian blur and use very lagre number (such as 50-80). For stronger blur, duplicate layer (Ctrl-J) and merge it back (Ctrl-E).
We only need glow outside the planet. To remove unnecessary glow, select layer with planet, set selection to layer transparency (you can hold Ctrl and click layer, or go to Select - Load selection - OK), then select layer with glow and hit Del to delete selected image.
The final touch is to set its lend mode to Color dodge.
To add a bit more 3D to our planet, create new layer, choose Brush tool, set brush size to very large (f.e. 700-800 pixels), set color o black, and add some black strokes on very bottom of image.