  Maxwell test fields as well as solutions of linearized gravity on the Kerr
exterior admit non-radiating modes, i.e. non-trivial time-independent
solutions. These are closely related to conserved charges. In this paper we
discuss the non-radiating modes for linearized gravity, which may be seen to
correspond to the Poincare Lie-algebra. The 2-dimensional isometry group of
Kerr corresponds to a 2-parameter family of gauge-invariant non-radiating modes
representing infinitesimal perturbations of mass and azimuthal angular
momentum. We calculate the linearized mass charge in terms of linearized
Newman-Penrose scalars.
