Imagine Earth waits for a comet hit. Three days and all life dies. Meanwhile, Elon Musk announces a space ark capable of traveling vast distances at light speed. People rush to fill the spaceship with everything important for a last ditch escape. The ark takes off for a distant planet identical to Earth in every way. Scientists believe the trip will save life and make humans a multi-planet species. The comet hits and Earth explodes.
The spaceship spends months getting to its destination and when it arrives, the planet is dead.