I’ve heard of making a sphere mesh inside of Max/Maya and giving it two uv sets (one of the poles and one for the belly) and then cross fading between those UV sets in UE, but I’m not quite sure what the best way to achieve this is yet. These are going to be procedural planets and baking my maps to the sphere is not an option before someone suggests it.
Some tip for making proper sphere for that mapping:
Create box first, slice every side to at least 4x4. Then Uv map all sides same way your texture is made, it is easier to adjust uvs on flat box sides. Then spherify it into ball.
If you want higher texture resolution, split that box into 6 separate material. one for each face.
Later if you want to add layer of clouds (and atmosphere shader) you need separate sphere mesh. For clouds it is best to make polar coordinate texture if you use spherified box you will have seams with any moving texture.
There was topic about making skybox, ATI and NVidia provide some tools to create spherical map out of 6 side textures.