[RockinRight]

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...

[SunkenCiv]

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.

Quibble -- the solar mass won't suddenly be reduced by expansion; also the expansion (if such occurs) will place part of the solar mass closer to the Earth, and as you know, distance is more important than mass. :')

Meanwhile, there's a transfer of momentum from a rotating parent body (in this case, the Sun) to each satellite in prograde orbit (Earth, among many others), which slowly but surely expands that orbit. A body in retrograde orbit migrates slowly but surely inward.