Huehuehuehue
It was originally a practical joke on a friend of mine who used to detest ponies (ironically, he's a fanatical brony now, go figure ) wherein he was coming to my place for a LAN party, and since I knew he would be using my desktop for AI War (he didn't have a laptop at the time) I went in and switched out one of the textures to little Rarity there. He was not amused. I never bothered to to change it out until the update with all the new planets came out and replaced my custom stuff.
So wait, that is PLANET RARITY? ~ponders~ Hmm... I would need an image converter I think... Or do some creative cropping... A new planet lists... I think I have at least 120 names...
Is a simple way to convert and existing image into the needed format to make a collection of pony planets?
Yes, it's very easy. If I remember, All I did was find the image, load it up in Photoshop to replace the whitespace with transparency and then save as PNG. Place it in the appropriate folder (something like AI War>RuntimeData>Logic>Images>Planets, but I don't remember exactly) and name it to have the same name as a planet. That's how I managed to have Earth, Coruscant, Rarity and a giant Superfortress as some of my planets.