PlanetSize.txt and creating new Sizes

[Suicide Junkie]

I just started playing with new planet sizes, and I tried to make a new planet size, smaller than "tiny". It would be a really small moon world, with one facility of you can breathe "none". Domed, you'd get no facilities, so you'd only be able to use it to grow people and build small units.

The thing ended up as having no picture, "--" for a surface type, "NA" for atmosphere type, optimal conditions, and normal resource value.

Does anybody here know how to add new Planet sizes properly? The text file has no hints .