3 body problem: orbital decay when there are three orbiting bodies of SIMILAR MASS.
Mercury is not similar mass to the sun, so this is not the three body problem
Mercury is not similar mass to the sun, so this is not the three body problem
The point is that a very small difference in starting conditions yield wildly different results.
https://www.google.com/url?sa=t&source=web&rct=j&opi=8997844...