I can't even open your scene it just crashes Maya, but we use 2011 so someone on 2012 might have better luck with it. That's huge though for a planetary system, try getting rid of all things generated from paint fx to start with.

You should use a project folders as well in Maya, when you start a new project go to file>project>new and that will sort your textures, renders and other things in a neat manner.

And when you upload files you should compress them, your 20 mb file is 3 mb if you compress it using something like winrar.