The fact that larger objects have a stronger gravatational pull then smaller ones has been proven by obeservation many times over and we can predict and have predicted how an object going by a larger body will travel based on this knowledge. It is the sun with its larger gravatational pull that makes the earth travel as it does so it therefore only makes sense to say that the earth goes around the sun and not the other way around.
Also according to the Rambam (yisodei hatorah 3:4) the sun is located in the sphere between mercury and mars wich would mean that there should be no planets between mercury and mars except for the sun. We now know that this is simply not true (we live on a planet between mercury and mars and we arn’t on the sun!).
We also find no mention of any planets other then those that were known at that time namley Mercury,Venus,Mars,Jupiter and Saturn we find no mention of either Uranus or Neptune (the reason why there are nine spheres mentioned by the rambam and others is because there was also beleived to be a sphere for the Moon, “Fixed stars” and “Prime mover” (5+3=9))