I think Nelson would know better than me, so I'll quote you and myself for clarity...
Idea> instead of drawing up new phases for each planet, why not make a selection of masks to put over them in the background editor? 
If it's feasible. Either the same colour as the default starfield.pof textured or some kind of freaky alpha map using SCPower to "erase/hide" a portion of the image file using layering maybe? :nervousagain: 
Assuming you can stack planet textures on top of each other and that it works well too. I don't know if that's even possible, but assuming it is...
I thought of that as well, but the problem is that in a full-lit version you would have the atmosphere surrounding the whole planet with a rather prominent glow. Now, if you would stack a shadow mask over it, you would need to stretch the shadow mask over the atmospheric glow of the underlying fully lit planet.
This would undoubtedly work pretty well, as long as the background doesn't have any nebulae on it. If it had any nebula behind the planet, the stretched shadow layer would visibly show up against the nebula, or at the very least it would be visibly larger than the lit side of the planet.
A possible solution would be to use a base texture of the planet without any atmospheric glow whatsoever, and overlay that with appropriate shadow/atmo-glow hybrid layer. But that would require the mission designer to stack the two planets on the correct positions, then rotate the shadow/glow layer to correct position, and on the user end it would end up using twice as much VRAM as simple baked-in shadow/glow planet image would. I have no idea how much of the actual rendering performance goes to the background and how much the performance would be hit, but every unnecessary bit is too much in my opinion...
Another thing is that with some planets (especially those that are on skybox use and thus are very high resolution) the direction from which the light supposedly comes from can pronounce terrain elevation (mountains) and it could look fairly stupid to have mountains on the surface of a planet and notice that they look more like canyons judging by the supposed lighting. 
That said, I need some opinions.
This is the retail planeta1.pcx:
What I need is opinion on whether this is supposed to be a water-covered planet with clouds on the atmosphere, OR an Uranus/Neptune-like mostly featureless gas giant?
I think it's supposed to be an oceanic planet/moon, for three reasons. One, it has a reflection, which points to clearly defined interface between shiny (liquid) surface and atmosphere. Gas giants just have clouds all over with respectable amount of albedo, but they don't produce glints or reflections like the surface of liquid or ice. Two, it has a very thick atmosphere in relation to the planet's diameter; gas giants don't really have visible atmo glows from the distance it takes to fit it onto the field of view entirely. Or, well, they do, but it's thickness is lost in the relative diameter of the planet, and doesn't even reach one pixel on these shots so it's not worth the trouble to get into them.
Three, the clouds seem much more like the ones on Earth than the ones seen on gas giants (though that's mostly just my edumacated opinion, but still).
Fourth point wold be the combination of reflection and the fact that the reflection is blue, which means that the atmosphere scatters blue light in very similar way as Earth's atmosphere does (since water itself is almost colourless, it's blue on Earth only because the atmosphere happens to scatter blue light the most and absorb other wavelengths more). On a cloudy day, water is grey...
I know that in current MediaVP's it's more like a gas giant, but I think that's a bit of a mistake... I personally am an advocate of a water planet (since the retail seems to point to that direction in my opinion), but I understand if people used to MediaVP interpretation would want to keep it more like gas giant.
So, I'm open to opinions.
EDIT: Here's a water planet as a possible replacement for planeta1, complete with five phases.
