Open a new document sized 3508 x 2480 pixels and 300 pixels/inch.. Then open another new document seized 1500 x 1500 pixels also at 300 pixels/inch. In the second document paste in the gas giant texture. Create a new layer and paste in the Clouds, set this layer to Screen and reduce the Opacity to 25%. Merge the two layers. This is optional depending on the Gas Giant texture you use, but if you want to alter it slightly or radically, go Filter > Liquify and alter as you see fit.
