Here goes the main trick:
- make image square (Image - Canvas size - set width equal height)
- Desaturate (Ctrl-Shift-U)
- Go to Filters - Distort - Spherize. Set amount to 80%, apply. Then, repeat this filter again. You will get map similar to this.

Then, copy this map and paste it to your file with planet. Resize layer and align it to planet. Then set layer blend mode to Overlay, and finally, go to Layer menu - Create Clipping Mask (so that map is only visible within planet shape).

That's all! One last touch is shadow (everything looks better with a bit of shadow). In new layer, use large black brush and draw shadow like this.

Then, go to Layer menu again - Create Clipping mask, and also set this layer blend mode to Soft Light.