The ONLY thing that puzzles me about this behavior is how scientists can think there is anything abnormal about this. Things are constantly in flux, but on galactic time scales.
OuR sun viewed in time-lapse photography probably sputters bright and dim all the time- we just dont see it because it takes thousands of years.
By the same token I bet our planets either move in and crash into the sun OR move away and fling out into space, ... eventlually.
"In this case, what we see is what was left behind after the planetary accretion disk dissipated and the tidal torques disappeared."
I think that explains it.
The theory (which actually makes sense) is that when the sun becomes a red giant, it will either vaporize Mercury and Venus (maybe Earth and Mars) and Earth and Mars will be scorched, but actually move somewhat away from the sun as it will have less mass at that time to hold onto the planets with.
That doesn't take into account the possibility of another star or alien body entering our solar system and throwing things off a bit...