Scenario run-down. Several billion years from now, Sol has finally exhausted its hydrogen supplies and has entered the red giant phase. It has already been increasing in lumosity for some time and Earth has become an uninhabitable desert. Humanity is a spacefaring species now and everyone has been evacuated in time to nearby star systems, along with a "Genetic Ark" of every life form ever recorded on Earth. Sol expands and engulfs the Earth (but not quite reaching Mars). Fast forward a few more hundreds of millions of years, it releases the halo and reduces to a white dwarf. At this point, humanity is settled in dozens of nearby systems, has become advanced in planetary engineering and starts to dabble in stellar engineering. An ambitious long-term project is put in motion: Restore the Earth to its pre-human state (and as much of the rest of the Solar System as possible) as a form of museum/memorial/preserve.
Before I start making up the necessary restoration tech, I need a realistic damage assessment. In particular:
- How will Earth emerge (if at all) out of this? As a space rock scorched beyond recognition? Will it simply melt down and disperse in the Sun's heat? Or from the friction of atmospheric drag? Or will the drag slow it down so it falls into the Sun's core? Surely its orbit will be affected.
- What about Venus and Mercury? I assume they will evaporate.
- What about Mars? It's been orbiting quite close to the red giant's surface.
- What about the gas planets?
- How will the halo that the red giant releases at the end of its cycle affect the whole Solar System in general?
EDIT: Human technology level at time of the event is not sufficient to counteract/stop/delay the event in any way. I'm interested only in the natural results of Sun going through the red giant phase and the impact this has on the Solar System.