No. 31: Jan-Feb 1984
A most satisfying element of support for Einstein's General Theory of Relativity (GR) has been its accounting for the residual precession of Mercury's orbit. In recent years, however, a rival explanation has been found in the non-symmetric gravitational field of the sun. Surface oscillations of the sun betray hidden internal rotation, which produces asymmetry in the sun's gravitational field. By applying the distorted field in predicting the orbit of Mercury and the minor planet Icarus, astronomers are more successful than when they use the GR. The authors of this paper claim that GR averages some 2 standard deviations off the mark, while results -using the nonsymmetrical gravitational field of the sun are right on the money!
(Campbell, L., et al; "The Sun's Quadrupole Moment and Perihelion Precession of Mercury," Nature, 305:508, 1983.)
Reference. For other explanations of the advance of Mercury's perihelion, see AHB1 in our Catalog: The Moon and the Planets. Ordering information at: here.