Yes the planets are muslims. Muslims means someone who has surrendered to Allah, or God or the creator. We can clearly see these planets following their set of rules, code of conduct, law and order or fulfilling their function. therefore your heart is a muslim, you lungs, you kidneys, they are all following Allahs laws, they are fulfilling their purpose.
are you as a human fulfilling your purpose in life?
So then all animals would be Muslims as well, since they are totally surrendered to God's laws and are fulfilling their purpose as the horse, worm, fish, pig, or goat that Allah created them to be?