  In very-low energy plasmas, the size of nanograins is comparable to the
distance (the so-called Landau length) at which the interaction energy of two
electrons equals their thermal energy. In that case, the grain's polarization
induced by approaching charged particles increases their fluxes and reduces the
charging time scales. Furthermore, for grains of radius smaller than the Landau
length, the electric charge no longer decreases linearly with size, but has a
most probable equilibrium value close to one electron charge. We give
analytical results that can be used for nanograins in cold dense planetary
environments of the outer solar system. Application to the nanodust observed in
the plume of Saturn's moon Enceladus shows that most grains of radius about 1
nm should carry one electron, whereas an appreciable fraction of them are
positively charged by ion impacts. The corresponding electrostatic stresses
should destroy smaller grains, which anyway may not exist as crystals since
their number of molecules is close to the minimum required for crystallization.
