As you move further in, the tidal forces would keep increasing and ultimately they exceed the strength of Phobos and that is when you would have a breakup. Tushar Mittal More Quotes by Tushar Mittal More Quotes From Tushar Mittal If the moon broke apart at 1.2 Mars radii, about 680 kilometers above the surface, it would form a really narrow ring comparable in density to that of one of Saturn’s most massive rings, over time it would spread out and get wider, reaching the top of the Martian atmosphere in a few million years, when it would start losing material because stuff would keep raining down on Mars. Tushar Mittal science