Okay, here's some advice:
The planets themselves aren't bad. In fact they look good (as good as the retail FS2 planets, given that the 8-bit PCX format rapes the colours on everything...), for what I can see from the indexed PCX format... But that format is unnecessary now, and also the way you've used it is a bit flawed.
First, there is no need to make planets PCX files any more. Alpha blended TGA or even better, DDS files work much better and also look better.
Secondly, if you insist on using PCX format, note that FS2 interprets bright green (0,255,0) as transparent. AS it is, the shadow areas on your planets will be transparent and the background stars and nebulae will be visible through your planets. Which, I daresay, is an unwanted effect...

If you have the originals, I would suggest taking them, making them power-of-two textures with alpha channel and correct transparency, and then convert them to DDS format. 1024x1024 resolution seems to be sufficient for most cases.