The facts about Mercury

Mercury is the in close proximity planet to the Sun and the eighth biggest. Mercury is somewhat slighter in diameter than the moons Ganymede and Titan but more than twice as enormous.

Mercury's orbit is exceptionally eccentric; at perihelion it is just 46 million km from the Sun but at aphelion it is 70 million. The position of the perihelion processes regarding the Sun at a very slow rate. 19th century astronomers made extremely careful explanation of Mercury's orbital parameters but could not sufficiently explain those using Newtonian mechanics. The tiny differences between the experimental and predicted values were a slight but nagging problem for many decades. It was thought that one more planet (sometimes called Vulcan) slightly nearer to the Sun than Mercury power account for the discrepancy. But in spite of much effort, no such planet was found. The real reply turned out to be much more dramatic: Einstein's General Theory of Relativity! Its right forecast of the motions of Mercury was a main factor in the early acceptance of the theory.