How to have my solar system stick that would be edible
It's really easier to do with icing, but if you make a really pale dough such as a sugar cookie dough, you can color it.

I once made pie-chart shaped cookies by doing this, then making wedges in various colors &amp; sizes, then squishing them all back together into a log, and slicing it into rounds.  I don't know if it was the colors that I was using, but I found that they lightened up a bit as the cookies baked, so you'll want to make the dough darker/deeper than desired.

The trick is in getting the mottled look of some of the planets -- what you want to do it color two or three chunks in the different colors found on the planet, and once they're each well blended, break them into little bits, then toss them together before squishing it all back into a single ball (or sheet).  You might want to be a little more specific in your squishing things back together with the earth, if you want to do the continents + oceans ... but you can cheat and do blue &amp; white (oceans + clouds) so you don't have to be as precise.

If you wanted to do it in icing, you can get the mottled look by loading two colors in the bag, so you get a little of each color with each squeeze.  A star tip will help to make each less distinctive.  You can see the effect at:


http://geeked.gsfc.nasa.gov/?p=5355  (scroll down 'til you see the orange bits)
https://www.flickr.com/photos/gsfc/4311777957  (top right one; waited 'til it crusted up a bit before I smoothed it down)