Earth & Space Cake

This cake is for the 1 year anniversary of my parent's church they started. They use space with earth on their website. This is chocolate with buttercream 1/4 sheet and then the half circle is vanilla with buttercream. I did the papertowel thing on it to give it a swirly look. I am happy with it. I originally was going to make it the full circle (sports ball pan), but the bottom cracked when I tried putting the circle together. Not sure why...Anyone??