The way I see it, there are definite relations between mass of a certain size and others. the problem is, if you build a similar to scale mini model on earth, they will not be attracted to each other, will they? If you had a rock the equivalent of the sun to even the moon, you would not see them brought together. This means there must be something special about the planets and the sun - not something unexplainable, but rather something like ions or magnetism or whatever. So, I would venture that planets are attracted to each other because of super mass! whatever that is! it is where there are kilo tons or terra tons of pressure on the planet, as it is made up of something, but, then why do gas giants also circle the sun? seeing as how gas giants circle the sun - caught in the cycle - it cannot have anything to do with mass. In fact, I suggest observing these giants would lead us to a better understanding of gravity with their asteroid belts than looking directly at the sun and earth examples. Now, if a gas giant has a lot of gasses attracted to each other, then the same can be said for the atoms in the chemicals or whatever that gas is inside the gas giants. Something is bringing them together, but what? more importantly, what is bringing the asteroids to the gas? insane! If there was a force out there that needs better understanding it is gravity. maybe we should look at the size of the gasses? maybe, the volume of the gasses is so massive it attracts asteroids together around it, and, all together, they circle the sun? So, if the gasses can be given mass, they must have an equivalent here on earth surely? how about if we were to observe the solar system as a big bed, and then suppose that the sun, being so big, lying in he centre of the bed, displaces the rest of the planets. then, these planets have somehow, without being able to slide down into the groove, are on a 'record player' with the rest of the solar system? eventually, they are all going to be in the centre of the bed, yes? of course now we might have a clue on how gravity works. Then, what about the gas giants? are they under similar circumstance? if they were, they would be in the centre of their own little world drawing the asteroids in. So, how does this 'bed' work? is it made of something very bendy or hardly bendy, or somewhere in between? If the bed was a lot of nothing - let's say we drop a few items down a 'well,' and make them all the same as the size ratio of the planets and sun, would they get closer together when they impacted the bottom of the 'well?' of course this needs to be tested, but, let's say they get closer together on the way down - that would be evidence! Then we could say these things are on a bed? Okay, so, there is very little gravity in space, but, we still will move. nothing in space is stationary, is it? this means that the pull force is very slight to the nearest star, or, that getting away from the nearest star will be fairly easy too. So, there is no gravity in space. these planets are merely only slightly attracted to each other because they are out of the gravity of the sun! the sun must have terribly powerful gravity, and, as soon as one of the planets enters the suns pull range... poof, it gets sucked in? This would mean that the planets are out of the range of the sun's gravity, for now, and that they are actually just travelling around. they started travelling around because there was an explosion, and for every reaction there is a further reaction. This means that, if the universe is to be understood, when you jump up, you fall down. now all the planets are falling down to the sun, but, they are still outside of the sun's gravity pull area. the air built up on our planet is compressed, so that gravity is very real here.