sentences:  The motion of the parent star indicates a minimum mass for Gliese 581d of 5.6 Earth masses (earlier analyses gave higher values).Dynamical simulations of the Gliese 581 system assuming that the orbits of the three planets are coplanar show that the system becomes unstable if the masses of the planets exceed 1.6–2 times the minimum values.Using earlier minimum mass values for Gliese 581d, this implies an upper mass limit for Gliese 581d of 13.8 Earth masses.