Prompted by a comment from Marcus (thanks for the great idea!), I have turned the paper planets into Christmas baubles.
They actually turned out very nice, and in mid-air from a tree gives off a much more planetary impression than when they sit on a shelf.
And they are easy to make, too. When assembling the planets, simlpy glue a looped thread to the top (from the inside). I actually had to attach the thread to the already finished planets, which I did like this:
I took thread (a green one, for better camouflage in the tree) and a couple of matches:
Broke off short pieces from the matches, and formed a loop with the thread:
Tied the thread at the non-loop end to the matches:
And finally, poked a hole into the top of the planets and pushed the match through (carefully, so that the thread would not slip off the match).
One note: The planets come in different sizes, to (very roughly) approximate their real sizes. If you want to decorate a tree with these, you may want to scale them so that they have roughly the same size. Below, you will find the planets scaled to the same size. In these templates, I have also left out the data on the bottom of the planets, as the text interferes with their use as baubles.