One interesting thing to keep in mind here is that life could even survive on Earth itself when the Sun dies. If the red giant phase of the Sun (before its col

One interesting thing to keep in mind here is that life could even survive on Earth itself when the Sun dies. If the red giant phase of the Sun (before its collapse) were to be just not quite hot enough to do more than scorch the surface of the earth and maybe heat the crust down only partially, microbial life would survive in deep fissures. Studies (link below) have shown that a whole ecosystem of life exists in wet cracks down to a depth of up to maybe 10 kilometers. Assuming the red giant phase of the sun only manages to cook the earth's surface, it's possible that the heat radiates down into the crust by a few hundred meters, or maybe a kilometer. After all, though rock as a dense object in your hand isn't a good thermal insulator, the porous, cracked substrate of our crust is indeed wonderful at insulating (second link). If it weren't we'd have long since cooked from the enormous heat beneath us. The same process works in the opposite direction. Thus IF, if the sun expands just enough to only scorch our world, once the sun collapses again and our planet enters its deep freeze, the microbes that survived far beneath its surface could live their strange existence indefinitely, close to magmatic heat sources in the delicately balanced equilibrium zones between these and the frozen world above. Yes, the core of the earth will also eventually cool too, but the combination of residual heat from formation, compressive friction heat and radioactive decay is enough to keep that from happening for at least tens of billions of years. It's a fascinating scenario to consider: the extreme limits of how tenacious life could stay alive on our world long after everything we consider sustaining is dead and gone. https://en.wikipedia.org/wiki/Deep_biosphere https://en.wikipedia.org/wiki/Deep_biosphere https://manoa.hawaii.edu/exploringourfluidearth/physical/ocean-floor/continental-movement-plate-tectonics#:~:text=Earth's%20solid%20crust%20acts%20as,to%20flow%20in%20convection%20currents. https://manoa.hawaii.edu/exploringourfluidearth/physical/oce...