I am writing a basic presentation for planet Mercury for my website. While doing a small research I came across an issue about Mercury's perihelion advance. I got the impression that GR theory which has explained it, is either not so accurate or there are other explanations. And I also came accross this:
"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.) "
Since I am not really qualified to figure out whether all these are accurate or not, could someone help me to clarify this issue, regarding Mercury's perihelion advance? Does GR actually explains and precisely calculates the planet's advance or not? Are there any other reasonable theories, that offer also satisfactory explanations and calculations?