Seveneves / Neal Stephenson.

When a catastrophic event renders the Earth a ticking time bomb, it triggers a feverish race against the inevitable. An ambitious plan is devised to ensure the survival of humanity far beyond our atmosphere. But unforeseen dangers threaten the intrepid pioneers, until only a handful of survivors remain. Five thousand years later after a catastropic event rendered the Earth a ticking time bomb, the progeny of a handful of outer space explorers, even distinct races now three billion strong, embark on yet another audacious journey: to return to Earth.