Are the planets Mercury, Saturn, Uranus and Neptune losing mass?
Anything that's working, spending energy is losing mass,  Einstein Mass-energy equivalence of SR along with radiant energy(electromagnetic and gravitational radiation) would be effecting all the planets, but at a different rate for each one.  https://en.m.wikipedia.org/wiki/Radiant_energy
  And.   https://en.m.wikipedia.org/wiki/Mass_in_special_relativity
  These should help I think