My Son is in 5th Grade and currently his class is studying the solar system. he wanted to know why only Gas giants had rings and the smaller planets did not. His Teacher apparently side stepped the question so he asked me. I assumed it is due to the Gravity but I didn't have enough information to explain in detail so I told him I would research it and get back to him. Google as I might, I cannot find any direct answers to this. most of my Google inquires come back with science fiction references. If anyone would be so kind as to give me some details I will gladly relay it to my Son. Thank you in advance.