A model-independent test of spatial variations of the Newtonian   gravitational constant in some extrasolar planetary systems
  In this paper we directly constrain possible spatial variations of the Newtonian gravitational constant G over ranges 0.01-5 AU in various extrasolar multi-planet systems. By means of the third Kepler's law we determine the quantity \Gamma_ XY=G_X/G_Y for each couple of planets X and Y located at different distances from their parent star: deviations of the measured values of \Gamma from unity would signal variations of G. The obtained results for \eta=1-\Gamma are found to be well compatible with zero within the experimental errors (\eta/\delta\eta= 0.2-0.3). A comparison with an analogous test previously performed in our Solar System is made. 
Lorenzo Iorio