At least the title of this thread is somewhat accurate.

The first part of our opening post isn't so bad, but then you start to display an assortment of false premises regarding what NASA has said and more importantly what the density of a comets tail is. (Sorry, I never mentioned the density of a comets tail? I point out, correctly that it's a mixture of dust and gasses!?) The coma/tail of a comet accounts for a small fraction of its mass and thus you cannot use the diameter of said coma/tail to determine its gravitational effects. (I think you'll find I was writing about the size of the nucleus mainly in theory to give a hypothetical viewpoint) I applaud you for trying to learn a little more about comets on your own, but you really need to gain a little bit better understanding regarding gravity, mass and density and such. (please see my other reply to this observation)