Experimental test of the variability of G using Viking lander ranging data

Results are presented from the analysis of solar system astrometric data, notably the range data to the Viking landers on Mars. A least-squares fit of the parameters of the solar system model to these data limits a simple time variation in the effective Newtonian gravitational constant to (0.2 +- 0.4) x 10-11 yr-1 and a rate of drift of atomic clocks relative to the implicit clock of relativistic dynamics to (0.1 +- 0.8) x 10-11 yr-1. The error limits quoted are the result of uncertainties in the masses of the asteroids