Please forgive me for how odd this question may sound. I just couldn't write it to make any more sense, and I do apologize for that. Mass, by what I know, doesn't seem to produce the amount of gravity that it should. Take the example of Jupiter: it has a mass approximately 300 times that of earth. However, almost all of this mass is composed of two incredibly light elements; hydrogen and helium. This combination, when condensed as a liquid or solid, would probably weigh no more than 3 pounds per cubic foot, if that. That is not very dense. Earth's composition is more complex, as can be seen here: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/elabund.html . Earth is approximately 50 percent hock rock that must have a much greater density than hydrogen or helium. Magma most likely weighs around 170 pounds per cubic foot (that is about the weight of granite). Half of that gives about 85 lbs per cubic foot.Therefore, earth's composition would be, approximately, over 25 times denser than Jupiters. So, Jupiter may have approximately 300 times the mass of earth, but only about 12 times the density (rough estimate). Materials weigh more because of DENSITY, right? The denser the material the greater the gravity it produces, correct? Isn't this why mercury is around the same size as the moons of some of our gas giants, and considerably smaller than mars, yet has greater gravity than any of the former and equal gravity to the latter? And thus I become so confused. Jupiter's gravity well is incredibly powerful, certainly far more than just 12 times as powerful/massive/influential, as the earth. It has a surface area over 100 times greater than earth. Even at the highest cloud tops--the "surface" of this gaseous planet--it has about 2.65 times the gravity of earth. 12 times greater, over that great a surface? That is strange; that much gravity must make a gravity well bigger; MUCH bigger than it should be given its density. Why does it have much more gravity than its density should allow? I just don't understand it. I've researched the subject considerably, but still can't figure it out. And I know that from the way I wrote it, I know it looks foolish but I can't think of a better way to phrase the question. Thanks for any and all help given.