To consider the existence of gravitons, as in quantum physics, is to completely disregard General relativity (im not saying GR is perfect but..). We know objects react instantly (or very fast anyway) to gravity and that to have gravitons means that they must travel faster than light.
So why are...
Comets are very small (like a few kilometers diameter i.e low gravity) and moving at speed throughout their orbit. I would imagine these combined factors would not be conducive to accumulation of ice/dust. A stationary (relative to other bodies) asteroid maybe... I can see how matter (that is...
The comet Tempel was found by a NASA probe to have only 6% water ice on the surface. To me, a comet core just looks like an asteroid. The NASA Deep impact pages really seemed to be trying to imply that they were correct all along. See for yourself - it just sounds very suspect. They still seem...