[Anonymous Rex]

And just what is going to change in the next 40 million that hasn’t changed in the first 4.2 billion that’s going to cause the problem?

[The_Reader_David]

Nothing. It’s just that a gravitational n-body system for n > 2 exhibits chaotic dynamics, and it’s possible that the system could move into a different part of the phase space just in the normal course of things.

[snarks_when_bored]

Small gravitational perturbations can produce really big orbit shifts over time. The solar system is a quasi-stable system at present, but it can become chaotic at pretty much any time...

[Camel Joe]

Well, the moon moves away from the earth by about an inch or half inch per annum. Without the moon we will lose our stable rotation and perhaps wobble into mars. (Bush's fault)