We know that iron atoms have maximum binding energy. As a consequence, the iron atom is lighter than the sum of constiuent nucleons when free from the atom. Since that weight of iron is measured  by gravity, the same thing must apply to objects on earth, i.e. we have binding energies (negative energy) in comparison to floating in free space. So are we also lighter by delta E=mc^2 on earth than we would be in space? This seems entirely logical, exactly the same as the iron atom. Although the weight difference may be small. Anyone?