First of all, combustion is happier if you use clips that run at the same frame rates. This will also simplefy the math you have to do to get the relationships of rotations later. You may want to render your clips out at 30 fps for example and re-import them into a workspace that is set at 30 fps as well. ( footage frame rate is in the Footage tab available when you select your clip in the workspace tree, and worksdpace framerate is found in the Composite Controls tab in Output made available when you select the topmost branch of the workspace tree.)
Otherwise you'll need to remap the timing of your clips. I don't have all the info, but I'll make up my own numbers and you should get the idea. Have your Sun layer rotate 1 time in 10 seconds. So you'll need it to spin once in 300 frames ( 30 frames / sec for 10 sec = 300 ). Select your Sun clip in the workspace tree ( not the layer-you'll have to twirl the layer open and select the actual clip,) and you should get the Footage Controls tab. In Footage Controls/ Output, you'll find a Time Stretch column. ( I'm working with version 2.1 - the newer versions have a time warper, but this will give you the idea.) Change the Duration field untill your Sun clip is 300 frames long. (This is based on your Sun layer at it's original duration was only one rotation. If there was more, if it shows more than one rotation, you'll need to trim your Sun layer in the Timeline so it is only 1 rotation.)
Next select the Earth clip and use Time Stretch so that it loops every 10 frames ( it's 10.34 exactly but I'm not sure the controls will allow fractions,) so that in the 300 frames it took your sun to spin, it will spin 30 times ( again you'll have to tweak the percentage to get it to exactly 29 spins and again, these are my numbers, I have no idea what you have.)
Something to consider. Drastically slowing footage, even if you enable Frame Blending will result in steppy playback, so if you have really short clips that you need to stretch quite a bit, it'll play back very choppy. The best is if your original, un-time stretched clips are long, like if the sun clip you have is actually 300 frames long for 1 rotation.
Hope this helps!
jon a