>>7
The theory mentioned is a major assertion of Einstein's theory of relativity - that gravity affects spacetime. The theory only covers for time slowing down and for light being pulled by gravity (at its extreme being unable to escape from a gravity well once caught); it never asserts anything about time reversing.
The problem with the "planet so large" postulate is that gravity is affected in some way by both mass and volume. A black hole, for instance, is considered to have one of the strongest gravity pulls for its size because all of the mass of its former star has been condensed into a minute region. "Time" at this singularity is said to have stopped, though that can only be mathematically proven. For a body of large size to have time stopped on it due to infinite spacetime curves, it would have had to have collapsed from another body of such size that it would dwarf even our concepts of the size of star systems. There is also the possibility that the substance of the planetoid is incredibly dense; size is not as much of an issue at that point, though