Hi there. As a molecular biologist my knowledge of physics is fairly limited to the topics I learnt before college, but recently I have developed an interest in learning a bit more about it. More to the point a certain question has been puzzling me for some time now and I was wondering if anyone with some expertise could help me. I'll start by stating what I do know: 1) All objects in the universe attract one another due to the force of gravity. 2) Gravity only has any real effect when very large masses are involved, such as stars or planets. 3) The force exherted by the gravity of an objet decreases exponentially as the distance from it increases. 4) The major forces we feel on Earth are due to the gravity of the sun (keeping us in orbit around it) and the gravity of the moon (causing tides amongst other things). My question is then; do the planets cause a significant force of attraction on each other, or are they too far apart and too small for the force to be registerable? I'd appreciate any help with this question, either as a direct answer, or just pointing me in the direction of some information that can allow me to learn how to figure it out for myself. Any calculations with exact data would be great as well.