I finally managed to render a planet, with clouds that looked at least convincing. After rendering, I saw that I had forgot to turn off GI (as recommended by many here), so I did a new render with both GI values in the rendering tab set to zero AND the enviro light values set to zero. The render took half the time, but I had to change the cloud color to a much lighter one, because they turned too dark. Also, I think there is a considerable difference between the 2 renders and, to tell the truth, I like the one with GI better.
Or is enviro light not a part of GI?
The image below is with GI.
Helen