by Jack Le Moine
Time: 6.5 BYF (billion years in the future)
Place: Sun’s outer atmosphere
It finally has happened. For a billion years, ever since the Sun started fusing helium instead of hydrogen, it has started loosing mass but gaining size and luminosity. Every year for a billion years it gained size and brightness while loosing weight. Its gas thinned each year as the Sun’s activity through off bits and pieces of the atmosphere’s top off into the planetary system.
Where was the Earth? Orbital mechanics dictated that as the Sun’s mass decreased, the Earth’s orbit increased. As the Sun reached the Earth’s orbit, the Earth had moved further out. It is now 70% further out. Unfortunately the habitable zone begins at 100% further out. This may not matter. Friction from all of the debris thrown off the Sun’s atmosphere will cause the Earth to slow down, decreasing its orbit. In addition, there’s tidal effects from the nearer Sun. The Sun’s lesser gravity cancels the rest of that; the Earth may still be right where it is at now.
But not for long. Tidal effects will be so great that it will rip the planet apart. — Unless the planet gets incinerated first.
What about humanity? Well, some of those large moons around Jupiter and the other gas giant planets are starting to look pretty good. Nice surface temperatures. Other environmental conditions not so good. It would be worth while to terraform them. The Sun will be here at this orbit for another billion years.
Estimates for when these events will take place vary. The video places Red Giant phase beginning in 7 BYF while articles give 6.4 BYF. All sources seem to agree on the sequence of future solar events, though.