  The effect of a cosmological constant on the precession of the line of
apsides is O(\Lambda c^2 r^3/GM) which is 3(H_\circ P)^2/8\pi^2 \approx
10^{-23} for a vacuum-dominated Universe with Hubble constant H_\circ = 65
km/sec/Mpc and for the orbital period P = 88 days of Mercury. This is
unmeasurably small, so planetary perturbations cannot be used to limit the
cosmological constant, contrary to the suggestion by Cardona & Tejeiro (1998).
