Coming back to an earlier topic, (after reading it in a french magazine), it turns out the Earth is actually too close to the Sun for it to be preserved when the Sun will inflate. Because of the drag coming from the Sun's external levels.
There will be an increase of the Earth's orbit radius, when the Sun looses its mass, but 10% further away won't be enough.
In 7.6 Billion years, a 35% less massive Sun, but 250 times fatter, will engulf our planet. In order to avoid that fate, the Earth had to be 20% further away from the Sun than it is today.....too far to be in the habitable zone? I don't know.