Matter v. Mass

I was reading an article on the Thunderbolts of the Gods site and I came across an explanation on the difference between matter and mass. We assume they are the same, or at least directly proportional. Turns out that's not the case.

An amount of matter is sensed, typically by our muscles. An amount of mass is determined by its relationship to perceived force and movement, m = F/a.

In order to measure mass and relate to matter, our physicists look at motion and forces and extrapolate based on how matter is sensed here on earth. This tends not not work out very well. Saturn has been calculated to weigh less than water, Mercury is posited to have a very dense core, Comets are fluffy ice despite looking like rocks, and, of course, there needs to be a hundred times more observed matter in the universe (so they made up dark matter and black holes).

Newtonian Movements need to be revised, this is totally out of control.