Ya its possible.
Need to copy an existing planet entity and rename to suit. Add to the entity manifest. Add to galaxysceneriodef. Increase counts on all.
Need to have a model imported to XSI so it can be exported to a .mesh file
Place the .mesh in the mods mesh folder and open the new planet entity and connect the new mesh.
Pace the textures for the mesh/model in the mods Textures directory.
Get that far and we can work on icons and strings.
http://soase.weebly.com/