My science question.Why are the planets different sizes

                                                                         
                             
                               

                        Why are the planets different sizes 


The theory is that the sun burned away matter from the inner planets,which is why these four are a very small rocky world .Mercury is very small but dense.Venus is almost as big as earth.Next is Jupiter ,the first and king of the gas giants.Jupiter is more massive.Mars is smaller than Venus. 
           
This is my science research, I hope you enjoyed it.