I've gone ahead and re-rendered all the Tiny Planets so they use a teal background instead of a black one, which should make them much easier to extract from the backgrounds! Every planet is exactly the same size, and rendered with the exact same pixels around the edges, so now you can easily just wipe out the background with the Fill Tool in Photoshop or Gimp, or using the website mentioned earlier to convert the Teal into a transparent background! The exact color value is R: 0 G: 128 B: 128